You may have heard every vitamin D myth under the sun—so many, in fact, that you might be at the point of throwing your hands up in the air in frustration. Why can’t there be a simple answer?
First, some facts: Your body needs vitamin D. Its main job is to help the body absorb calcium from the intestines. This calcium is necessary to help “mineralize the skeleton” over the course of your lifetime and is a critical mineral for forming the hardened bone that keeps you strong and healthy.
On the other hand, “not getting enough Vitamin D can have serious consequences, including increased rates of bone loss or even osteomalacia (‘soft bones’) in adults and rickets (a deforming bone disorder) in children,” says Yale Medicine endocrinologist Karl Insogna, MD, director of the Yale Medicine’s Bone Center.
- How do you get vitamin D?
- How does the body process vitamin D?
- The final verdict on vitamin D
- Vitamin D Supplements & Foods
- What Is Vitamin D?
- Why Is Vitamin D Necessary?
- What Are The Signs Of A Deficiency?
- How Much Vitamin D Should Adults Take?
- How Much Vitamin D Should Children Take?
- What Are Some Vitamin D Foods?
- Are There Any Risks Associated With Too Much Vitamin D?
- Mayo Clinic Q and A: How much vitamin D do I need?
- How to Pick the Best Vitamin D Supplement
- Vitamin D
- Vitamin D
How do you get vitamin D?
The short answer is from food, the sun or supplements.
There are two main kinds of vitamin D—vitamin D2 and vitamin D3—which you can get from (and occur naturally in) certain foods like salmon, tuna, mackerel and beef liver and egg yolks. But because we don’t consume large enough quantities of these foods, they can’t be our sole source of vitamin D. That’s why foods like milk, cereal and some orange juices are vitamin D2- and D3-fortified. (Since the 1930s, manufacturers have voluntarily enriched these foods with vitamin D to help reduce the incidence of nutritional rickets.)
When exposed to the sun, your skin can manufacture its own vitamin D. “We each have vitamin D receptor cells that, through a chain of reactions starting with conversion of cholesterol in the skin, produce vitamin D3 when they’re exposed to ultraviolet B (UVB) from the sun,” says Yale Medicine dermatologist David J. Leffell, MD, chief of Dermatologic Surgery.
Another avenue to get vitamin D is by taking supplements. These come in both pill and liquid form. They are generally recommended for people with fat absorption issues, lactose intolerance, milk allergies, as well as for people with darker skin tones or with certain medical conditions that prevent them from going outdoors.
How does the body process vitamin D?
After vitamin D is absorbed through the skin or acquired from food or supplements, it gets stored in the body’s fat cells. Here it remains inactive until it’s needed. Through a process called hydroxylation, the liver and kidneys turn the stored vitamin D into the active form the body needs (called calcitriol). In case you were wondering, it doesn’t matter if you’re getting D2 or D3, and the sunlight-generated kind isn’t better than the nutritional variety. “The body can use each perfectly fine,” says Dr. Insogna.
Those are the basic facts, but some questions might remain: How should you get vitamin D? How much should you get and when should you worry about your levels? In light of these common questions, our Yale Medicine doctors help clear up some confusion about vitamin D, separating fact from fiction.
The more vitamin D you take, the better? Absolutely not.
—Thomas Carpenter, MD, Yale Medicine pediatric endocrinologist and director of the Yale School of Medicine’s Center for X-Linked Hypophosphatemia
That’s a misconception. Vitamin D is stored in fat. So, if you’re a small person and getting large doses, you have less available storage, which means vitamin D goes into your blood and you may absorb too much calcium, creating a toxic situation. And it’s unclear how long you have until you exceed the upper limits of vitamin D intake before it becomes dangerous. (Modest increases above the RDA are not likely to cause harm.)
Just recently, I treated an infant whose blood vitamin D level was in the hundreds when it should have been between 20 and 50 nanograms/milliliter (ng/mL). The child, who developed high blood calcium (hypercalcemia), had to be hospitalized and treated with several types of medications to get the calcium levels down to normal levels.
You can now get 50,000 IU tablets over the counter. There are patients with specific issues who might need a prescription for high levels of vitamin D, but for most people, that amount will raise your vitamin D level too high.
When shopping for supplements, always look for ones that offer the daily recommended allowance (RDA) you need for your age bracket: For most healthy people, it’s 600 IU per day, but for people over age 70 who need a little more—it’s about 800 IU. That’s because, as people age (women after menopause, in particular), they less efficiently synthesize vitamin D and absorb calcium. Babies should be getting smaller amounts in their first year of life, between 200 and 400 IU.
Should everyone get their vitamin D levels checked? Generally, no.
—Karl Insogna, MD, director of Yale Medicine’s Bone Center
Most people should be fine. Testing is important only for certain populations: for people who are institutionalized; for patients with a gastrointestinal disorder (like inflammatory bowel disease) or osteoporosis; those who have had weight loss surgery; those on anti-convulsant medications; and children who are immobilized and not outside and active. If you’re over 70, I recommend getting your levels checked at least one time.
People whose cultural or religious beliefs require them to be fully clothed, especially if they’re living in northern climates, and whose dietary habits include little or no dairy (which is vitamin-D-fortified), may also be vitamin D-deficient and should be tested.
Is vitamin D deficiency an epidemic? No, it’s not.
—Thomas Carpenter, MD, Yale Medicine pediatric endocrinologist and director of the Yale School of Medicine’s Center for X-Linked Hypophosphatemia
Based on the United States Dietary Association (USDA) and National Health and Nutrition Surveys (and using 20ng/mL as the lower limit), the bulk of the population is not vitamin D-deficient. The population we tend to see vitamin D deficiency in—and it’s typically in wintertime—are breastfed infants. Breast milk doesn’t have much vitamin D in it. That’s what spurred a recommendation from the American Academy of Pediatrics that every breastfed infant be given vitamin D (if they’re being given liquid multivitamin drops, they’re getting enough of it). But if infants aren’t given multivitamin drops, they need to be given 200 IU a day of vitamin D for the first two months of life and 400 units a day afterwards until they’re drinking formula or milk, which are each fortified with vitamin D.
Is it best to get your vitamin D from the sun? Definitely not!
—David J. Leffell, MD, Yale Medicine dermatologist and chief of Dermatologic Surgery
One of the biggest challenges we’ve faced in dermatology and in the world of skin cancer prevention has been a lot of misinformation about vitamin D metabolism.
There are claims that one needs to get a certain amount of sun exposure every day in order to produce enough vitamin D to be healthy. It’s just not true. The majority of people can get their vitamin D from nutritional supplements and from vitamin D-fortified foods.
There are some people (who are typically not dermatologists or experts in the biology of skin cancer) who have advocated for tanning to get vitamin D. But we know that UVB light causes skin cancer and that protecting yourself against it makes sense. As a doctor who treats patients who have melanomas, I want the general public to be advised that under no circumstances can use of a tanning bed or tanning in general be justified on the basis of vitamin D. Take a supplement instead.
The final verdict on vitamin D
No bones about it, the endocrinologists we interviewed agree with our dermatologist.
“Just being outdoors, you get a fair amount of sun exposure and some sun-related generation of vitamin D,” says Dr. Insogna. “Because skin cancer, particularly melanoma, can be such a devastating disease, it’s best to use sunblock when outdoors in strong sunlight for any prolonged length of time. Because this may limit the amount of vitamin D you get from sun exposure, make sure your diet includes sources of vitamin D from foods or supplements,” he says.
Both your skin and your bones will thank you.
. Or to make an appointment call 203-737-1932.
Vitamin D Supplements & Foods
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What Is Vitamin D?
Vitamin D, often referred to as the “sunshine vitamin,” is actually a fat-soluble hormone that the body can synthesize naturally. There are several forms, including two that are important to humans: D2 and D3. Vitamin D2 (ergocalciferol) is synthesized by plants, and vitamin D3 (cholecalciferol) is synthesized by humans when skin is exposed to ultraviolet-B (UVB) rays from sunlight. The active form of the vitamin is calcitriol, synthesized from either D2 or D3 in the kidneys. Vitamin D helps to maintain normal blood levels of calcium and phosphorus.
Why Is Vitamin D Necessary?
Vitamin D assists in the absorption of calcium and promotes bone mineralization, which may prevent or slow the progression of osteoporosis. It also helps to strengthen the immune system and protect against a number of serious diseases, including rickets and osteomalacia. Research suggests vitamin D may also provide protection from hypertension, psoriasis, several autoimmune diseases (including multiple sclerosis and rheumatoid arthritis), and reduce the incidence of fractured bones. In addition, growing evidence has demonstrated its important role in defending against cancer (studies link a deficiency of vitamin D to as many as 18 different cancers).
What Are The Signs Of A Deficiency?
Deficiencies of vitamin D are common, especially in industrialized countries in northern latitudes, where sun exposure is typically infrequent. Low levels of vitamin D may be indicated by porous bones, weak muscles and easy fracturing.
How Much Vitamin D Should Adults Take?
According to the National Institutes of Health (NIH), the daily Adequate Intake (AI) for adults is 5 mcg (200 IU) daily for males, female, and pregnant/lactating women under the age of 50. People 50 to 70 years old should get 10 mcg daily (400 IU) daily, and those over 70 should get 15 mcg daily (600 IU). Based on recent research, Dr. Weil recommends 2,000 IU of vitamin D per day. Look for supplements that provide D3 (cholecalciferol) rather than D2 (ergocalciferol). Anyone with vitamin D deficiencies should discuss intake levels with his or her physician.
How Much Vitamin D Should Children Take?
According to the NIH, AI for children from birth until 5 years of age should take 5 mcg per day (200 IU).
What Are Some Vitamin D Foods?
It isn’t easy to get enough vitamin D from your diet. While fortified vitamin D foods such as milk and cereals are available, most provide vitamin D2, a form which is much less well utilized by the body than D3. Good dietary sources include fortified foods, eggs, salmon, tuna, mackerel and sardines. Since sunlight causes our bodies to make vitamin D, daily exposure is helpful. A helpful rule: estimate the amount of time it would take for your skin to turn pink – or slightly, but noticeably darker – in the sun. Then reduce that time by 50 percent if you have fair skin, 25 percent for darker skin, and get that amount of exposure between 11 a.m. and 3 p.m. two to three times per week.
Are There Any Risks Associated With Too Much Vitamin D?
No adverse effects have been seen with supplemental vitamin D intakes up to 10,000 IU daily. Exposing the face and hands to roughly 10 minutes of direct sunlight daily is also quite safe and a good way to boost vitamin D; for some tips on general sun safety, read the DrWeil.com Q&A: “No Fun in the Sun.”
Mayo Clinic Q and A: How much vitamin D do I need?
DEAR MAYO CLINIC: I have heard different recommendations from different sources regarding vitamin D. One doctor told my husband that everyone living in the Northern Hemisphere should take a vitamin D supplement every day, even in the summer. What do you recommend?
ANSWER: Understanding how much vitamin D you need can be confusing because there are different recommendations about how much vitamin D adults should get. Using the recommendations that fall on the low end, many adults don’t get the amount of vitamin D they should. Because few foods contain vitamin D naturally, eating foods fortified with vitamin D and taking a supplement may be beneficial.
Vitamin D is important because it helps your body sustain normal levels of calcium and phosphorus. Because it works as a key that allows your body to absorb calcium, vitamin D plays a critical role in forming and maintaining healthy bones. It also helps keep your muscles, nerves and immune system healthy.
Research suggests that consistently getting enough vitamin D can significantly lower the risk for the bone-thinning disease osteoporosis. Low vitamin D also is associated with falls, multiple sclerosis, rheumatoid arthritis, chronic pain, diabetes, high blood pressure, cardiovascular disease and some cancers. However, an association does not mean low vitamin D causes these conditions, or that taking a vitamin D supplement will adequately prevent or treat them.
Vitamin D is found in some foods, such as egg yolks, cheese, cod liver oil, beef liver and fatty fish like tuna, salmon, sardines, herring and mackerel. But the amount of vitamin D in these foods is quite small. In the U.S., many people get the bulk of their dietary vitamin D from foods that are fortified with it, including milk, cereals and some brands of yogurt and orange juice.
In general, even with fortified foods, diet usually doesn’t provide enough vitamin D. And certain health conditions that affect the gastrointestinal tract may decrease the absorption of vitamin D and predispose to low vitamin D blood levels. You also can get vitamin D through direct exposure to sunlight, although the amount of sun you need to get enough vitamin D can vary greatly.
For people in northern climates or those who spend most of their time indoors, adequate exposure to sunlight can be hard to get. Also, if you regularly wear sunscreen with a sun protection factor higher than eight — a wise move to protect your skin from cancer — or if you have a darker skin tone, you may not be absorbing vitamin D, even when you are out in the sunshine.
Recommendations for how much daily vitamin D adults need through diet have changed over the years. Currently, different recommendations exist. The Institute of Medicine has placed the recommended dietary allowance, or RDA, for vitamin D at 600 international units (IU) per day for young adults and 800 IU per day for adults older than 70. Other experts suggest that adults’ vitamin D needs are much higher. For example, the Endocrine Society recommends up to 1,500 to 2,000 IU of vitamin D daily for adults.
Mayo Clinic recommends that adults get at least the RDA of 600 IU. However, 1,000 to 2,000 IU per day of vitamin D from a supplement is generally safe, should help people achieve an adequate blood level of vitamin D, and may have additional health benefits. While there are no guidelines for checking your vitamin D blood level, it may be prudent in people with osteoporosis or certain other health conditions. Discuss with your health care provider if it may be beneficial to check your vitamin D level.
If you have ongoing health concerns or a chronic health condition, talk to your health care provider before you begin taking any dietary supplement, including vitamin D. He or she can help you decide if supplements are appropriate for your situation. — Dr. Donald Hensrud, Preventive Medicine, Mayo Clinic, Rochester, Minnesota
How to Pick the Best Vitamin D Supplement
At least 77 percent of American adults have low levels of vitamin D, according to research in JAMA Internal Medicine -and many experts believe deficiencies are even more common in the winter, when our skin is rarely exposed to the sun. That’s a problem, since shortfalls in “the sunshine vitamin” have been linked to some pretty scary outcomes, including soft bones, seasonal affective disorder and even an increased risk of death from issues like cancer and heart disease.
The easy fix? Supplements. (Bonus: They can boost athletic performance too.) But not all vitamin D pills are created equal, as a recent review of 23 vitamin D-containing products conducted by independent testing company ConsumerLab.com found. (Shape readers can get 24-hour access to the report, which is usually under a paywall, here.) So we asked ConsumerLab.com president Tod Cooperman, M.D., how to spot the safest, most effective options out there.
Rule #1: Remember, more isn’t always better
First things first: Yes, it’s hard to get vitamin D in the winter and yes, shortfalls have some scary side effects, while supplementing has pretty great-sounding perks (like warding off weight gain, for one). But getting too much vitamin D can also be harmful, says Cooperman. Your safest bet, he says, is to get your vitamin D levels tested before choosing a dose. Until you can, avoid taking more than 1,000 IU per day and beware of signs of vitamin D toxicity, like nausea and weakness.
Rule #2: Look for third-party certification
ConsumerLab.com’s report found that some supplements contained more than 180 percent more vitamin D than their labels stated, which-as Cooperman pointed out above-can increase your risk of an overload. Other research published in JAMA Internal Medicine had similar findings, and the study authors offered an easy enough fix: Check vitamin D bottles for a USP verification seal, which indicates the supplement went through voluntary independent quality testing. These pills listed their amounts most accurately.
Rule #3: Opt for liquids or gel caps
There’s a small risk that caplets (coated pills-they’re general solid colored) won’t break apart in your stomach, which inhibits the amount of vitamin D you actually absorb, says Cooperman. “But that’s not an issue with capsules, soft gels, liquids, or powders.” (What you eat when you take it also affects absorption. Are You Taking Your Vitamin D Supplement Wrong?)
Rule #4: Go for vitamin D3
There are two forms of supplemental vitamin D-D2 and D3. Cooperman recommends going with the latter, since it’s the type of D that’s produced naturally by our skin and is therefore slightly easier for the body to absorb. If you’re vegan, however, you may be better off opting for the D2, since it’s produced using yeast or mushrooms; D3 is often made from a derivative sheep’s wool.
- By Mirel Ketchiff
In supplements and fortified foods, vitamin D can be either D2 or D3. The two forms have traditionally been regarded as equivalent based on their ability to cure rickets, but evidence suggests that vitamin D3 is approximately three times more effective at maintaining serum concentrations because the binding protein has a higher affinity to vitamin D3 than vitamin D2. This allows vitamin D3 to reside in the circulatory system longer and increase the concentration to sufficient levels more quickly. The major preparations of vitamin D for prescription use in North America are in the form of vitamin D2, while more over-the-counter vitamin / multivitamin preparations use vitamin D3.
Whether it is absorbed through unprotected skin or ingested then absorbed by the intestines, vitamin D is bound to the binding protein (both albumin and vitamin D binding protein) and carried to the liver via the bloodstream. From there it begins two hydroxylation processes. Beginning in the liver it is transformed into 25(OH)vitamin D (calcidiol), which is the primary circulating form of Vitamin D and the most commonly measured form in serum. Then in the kidneys it is transformed into 1,25 dihydroxy-vitamin D (calcitriol), which is the biologically active form of vitamin D.
Table of Contents
- Vitamin D Deficiency: A Global Concern
- Vitamin D Sources and Function
- Bone and Muscle Strength
- Heart Disease
- Immune Function
- Multiple Sclerosis
- Type 1 Diabetes
- Flu and Colds
- Risk of Premature Death
Vitamin D Deficiency: A Global Concern
If you live north of the line connecting San Francisco to Philadelphia and Athens to Beijing, odds are that you don’t get enough vitamin D. The same holds true if you don’t get outside for at least a 15-minute daily walk in the sun. African-Americans and others with dark skin, as well as older individuals, tend to have much lower levels of vitamin D, as do people who are overweight or obese.
Worldwide, an estimated 1 billion people have inadequate levels of vitamin D in their blood, and deficiencies can be found in all ethnicities and age groups. (1–3) Indeed, in industrialized countries, doctors are even seeing the resurgence of rickets, the bone-weakening disease that had been largely eradicated through vitamin D fortification. (4–6)
Why are these widespread vitamin D deficiencies of such great concern? Because research conducted over the past decade suggests that vitamin D plays a much broader disease-fighting role than once thought.
Being “D-ficient” may increase the risk of a host of chronic diseases, such as osteoporosis, heart disease, some cancers, and multiple sclerosis, as well as infectious diseases, such as tuberculosis and even the seasonal flu.
Currently, there’s scientific debate about how much vitamin D people need each day. The Institute of Medicine, in a long-awaited report released on November 30, 2010 recommends tripling the daily vitamin D intake for children and adults in the U.S. and Canada, to 600 IU per day. (7) The report also recognized the safety of vitamin D by increasing the upper limit from 2,000 to 4,000 IU per day, and acknowledged that even at 4,000 IU per day, there was no good evidence of harm. The new guidelines, however, are overly conservative about the recommended intake, and they do not give enough weight to some of the latest science on vitamin D and health. For bone health and chronic disease prevention, many people are likely to need more vitamin D than even these new government guidelines recommend.
Vitamin D Sources and Function
Vitamin D is both a nutrient we eat and a hormone our bodies make. Few foods are naturally rich in vitamin D, so the biggest dietary sources of vitamin D are fortified foods and vitamin supplements. Good sources include dairy products and breakfast cereals (both of which are fortified with vitamin D), and fatty fish such as salmon and tuna.
For most people, the best way to get enough vitamin D is taking a supplement, but the level in most multivitamins (400 IU) is too low. Encouragingly, some manufacturers have begun adding 800 or 1,000 IU of vitamin D to their standard multivitamin preparations. If the multivitamin you take does not have 1,000 IU of vitamin D, you may want to consider adding a separate vitamin D supplement, especially if you don’t spend much time in the sun. Talk to your healthcare provider.
Two forms of vitamin D are used in supplements: vitamin D2 (“ergocalciferol,” or pre-vitamin D) and vitamin D3 (“cholecalciferol”). Vitamin D3 is chemically indistinguishable from the form of vitamin D produced in the body.
The body also manufactures vitamin D from cholesterol, through a process triggered by the action of sunlight on skin, hence its nickname, “the sunshine vitamin.” Yet some people do not make enough vitamin D from the sun, among them, people who have a darker skin tone, who are overweight, who are older, and who cover up when they are in the sun. (1)
Correctly applied sunscreen reduces our ability to absorb vitamin D by more than 90 percent. (8) And not all sunlight is created equal: The sun’s ultraviolet B (UVB) rays—the so-called “tanning” rays, and the rays that trigger the skin to produce vitamin D—are stronger near the equator and weaker at higher latitudes. So in the fall and winter, people who live at higher latitudes (in the northern U.S. and Europe, for example) can’t make much if any vitamin D from the sun. (8)
Low Vitamin D: What Increases The Risk?
Our bodies can obtain vitamin D from diet and make it from sun exposure. Even with these two routes for obtaining vitamin D, however, inadequate vitamin D is common, and deficiencies can be found on all continents, in all ethnic groups, and across all ages—a major concern, given the many ways that vitamin D helps protect our health. (1) There are a number of factors that increase the risk of having inadequate vitamin D, among them, lifestyle, sunscreen use, geographic location, skin tone, age, and body weight.
- Lifestyle: People who spend less time outdoors, or who cover up with clothing when they are outdoors, get less exposure to the sun, so they make less vitamin D. (1)
- Sunscreen Use: Correctly-applied sunscreen blocks the harmful ultraviolet B rays that cause skin cancer, but it also blocks most of the skin’s production of vitamin D. So people who use sunscreen daily are more likely to be low in vitamin D. (1) But don’t ditch the sunscreen: The American Academy of Dermatologists says that sunlight exposure to unprotected skin increases the risk of skin cancer, and that there’s no safe level of sunlight exposure that allows you to make vitamin D without increasing skin cancer risk. Their advice? Use sunscreen or other sun protection daily, skip the tanning booths, and get your vitamin D from diet or supplements. (2) Some Vitamin D experts take issue with the American Academy of Dermatologists’ hard line on sun exposure, and they recommend a more moderate option: Put sunscreen on your face, and allow your arms and legs to get a small amount of unprotected sun exposure—say, 15 minutes max—before applying sunscreen or covering up. It’s still a matter of scientific debate.
- Geographic Location and Season: In the summer, if you sat out in a bathing suit on a sunny afternoon for long enough to turn your skin slightly pink, you could make plenty of vitamin D. Yet during the late autumn and winter, people who live at higher latitudes produce little or no vitamin D from the sun, because the sun is at too low an angle in the sky. In the northern hemisphere, people who live in Boston (U.S.), Edmonton (Canada), and Bergen (Norway) can’t make enough vitamin D from the sun for 4, 5, and 6 months out of the year. (3) In the southern hemisphere, residents of Buenos Aires (Argentina) and Cape Town (South Africa) can make far less vitamin D from the sun during their winter months (June through August) than they can during their spring and summer. (3) The body stores vitamin D from summer sun exposure, but it must last for many months. By late winter, many people in these higher-latitude locales are deficient. (1)
- Skin Tone: People who have a darker skin tone have more melanin in their skin, and this pigment is a “natural sunscreen” that slows down skin production of vitamin D. (3) This the main reason why African Americans are more likely to be low in vitamin D. (4)
- Age: The ability to make vitamin D in the skin drops as we age, and is one of the reasons why older individuals are more likely to have low vitamin D levels. (1)
- Body Weight: People with excess body fat have lower vitamin D levels, so those who are overweight or obese have a higher risk of having inadequate vitamin D. (1, 5, 6)
The bottom line: Low vitamin D can be found in all ethnic and age groups, around the world, for a host of reasons. Even if you are taking a standard multiple vitamin, the amount of vitamin D in most vitamins (400 IU) is not enough to prevent low blood levels. If you suspect that you are at risk of vitamin D deficiency, you can ask your physician to order a blood test for vitamin D.
- Holick MF. Vitamin D deficiency. N Engl J Med. 2007; 357:266-81.
- American Academy of Dermatologists. 2010. Position statement on vitamin D.
- Holick MF. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. Am J Clin Nutr. 2004; 79:362-71
- Ginde AA, Liu MC, Camargo CA, Jr. Demographic differences and trends of vitamin D insufficiency in the US population, 1988-2004. Arch Intern Med. 2009; 169:626-32
- Rodriguez-Rodriguez E, Navia B, Lopez-Sobaler AM, Ortega RM. Vitamin D in overweight/obese women and its relationship with dietetic and anthropometric variables. Obesity (Silver Spring). 2009; 17:778-82
- Wortsman J, Matsuoka LY, Chen TC, Lu Z, Holick MF. Decreased bioavailability of vitamin D in obesity. Am J Clin Nutr. 2000; 72:690-3.
Vitamin D helps ensure that the body absorbs and retains calcium and phosphorus, both critical for building bone. Laboratory studies show that vitamin D can reduce cancer cell growth and plays a critical role in controlling infections. Many of the body’s organs and tissues have receptors for vitamin D, and scientists are still teasing out its other possible functions.
Vitamin D and Bone and Muscle Strength
Several studies link low vitamin D levels with an increased risk of fractures in older adults, and they suggest that vitamin D supplementation may prevent such fractures—as long as it is taken in a high enough dose. (9–13)
A summary of the evidence comes from a combined analysis of 12 fracture prevention trials that included more than 40,000 elderly people, most of them women. Researchers found that high intakes of vitamin D supplements—of about 800 IU per day—reduced hip and non-spine fractures by 20 percent, while lower intakes (400 IU or less) failed to offer any fracture prevention benefit. (13)
Vitamin D may also help increase muscle strength, which in turn helps to prevent falls, a common problem that leads to substantial disability and death in older people. (14–16) Once again, vitamin D dose matters: A combined analysis of multiple studies found that taking 700 to 1,000 IU of vitamin D per day lowered the risk of falls by 19 percent, but taking 200 to 600 IU per day did not offer any such protection. (17)
A recent vitamin D trial drew headlines for its unexpected finding that a very high dose of vitamin D increased fracture and fall risk in older women. (18) The trial’s vitamin D dose—500,000 IU taken in a once-a-year pill—was much higher than previously tested in an annual regimen. After up to 5 years of treatment, women in the vitamin D group had a 15 percent higher fall risk and a 26 percent higher fracture risk than women who received the placebo.
It’s possible that giving the vitamin D in one large dose, rather than in several doses spread throughout the year, led to the increased risk. (18) The study authors note that only one other study—also a high-dose, once-a-year regimen—found vitamin D to increase fracture risk; no other studies have found vitamin D to increase the risk of falls. Furthermore, there’s strong evidence that more moderate doses of vitamin D taken daily or weekly protect against fractures and falls—and are safe.
So what is the significance of this study for people who want to take vitamin D supplements? A reasonable conclusion would be to continue taking moderate doses of vitamin D regularly, since these have a strong safety record, but to avoid extremely high single doses. This recent finding does present a challenge to scientists who will work to understand why the extreme single dose appears to have adverse effects.
Vitamin D and Heart Disease
The heart is basically a large muscle, and like skeletal muscle, it has receptors for vitamin D. (19) So perhaps it’s no surprise that studies are finding vitamin D deficiency may be linked to heart disease. The Health Professional Follow-Up Study checked the vitamin D blood levels in nearly 50,000 men who were healthy, and then followed them for 10 years. (20) They found that men who were deficient in vitamin D were twice as likely to have a heart attack as men who had adequate levels of vitamin D. Other studies have found that low vitamin D levels were associated with higher risk of heart failure, sudden cardiac death, stroke, overall cardiovascular disease, and cardiovascular death. (21–24) How exactly might vitamin D help prevent heart disease? There’s evidence that vitamin D plays a role in controlling blood pressure and preventing artery damage, and this may explain these findings. (25) Still, more research is needed before we can be confident of these benefits.
Vitamin D and Cancer
Nearly 30 years ago, researchers noticed an intriguing relationship between colon cancer deaths and geographic location: People who lived at higher latitudes, such as in the northern U.S., had higher rates of death from colon cancer than people who live closer to the equator. (26) Many scientific hypotheses about vitamin D and disease stem from studies that have compared solar radiation and disease rates in different countries. These can be a good starting point for other research but don’t provide the most definitive information. The sun’s UVB rays are weaker at higher latitudes, and in turn, people’s vitamin D levels in these high latitude locales tend to be lower. This led to the hypothesis that low vitamin D levels might somehow increase colon cancer risk. (2)
Since then, dozens of studies suggest an association between low vitamin D levels and increased risks of colon and other cancers. (1,27) The evidence is strongest for colorectal cancer, with most (but not all) observational studies finding that the lower the vitamin D levels, the higher the risk of these diseases. (28–38) Vitamin D levels may also predict cancer survival, but evidence for this is still limited. (27) Yet finding such associations does not necessarily mean that taking vitamin D supplements will lower cancer risk.
The VITAL trial will look specifically at whether vitamin D supplements lower cancer risk. It will be years, though, before it releases any results. It could also fail to detect a real benefit of vitamin D, for several reasons: If people in the placebo group decide on their own to take vitamin D supplements, that could minimize any differences between the placebo group and the supplement group; the study may not follow participants for a long enough time to show a cancer prevention benefit; or study participants may be starting supplements too late in life to lower their cancer risk. In the meantime, based on the evidence to date, 16 scientists have circulated a “call for action” on vitamin D and cancer prevention: (27) Given the high rates of vitamin D deficiency in North America, the strong evidence for reduction of osteoporosis and fractures, the potential cancer-fighting benefits of vitamin D, and the low risk of vitamin D supplementation, they recommend widespread vitamin D supplementation of 2000 IU per day. (27)
Vitamin D and Immune Function
Vitamin D’s role in regulating the immune system has led scientists to explore two parallel research paths: Does vitamin D deficiency contribute to the development of multiple sclerosis, type 1 diabetes, and other so-called “autoimmune” diseases, where the body’s immune system attacks its own organs and tissues? And could vitamin D supplements help boost our body’s defenses to fight infectious disease, such as tuberculosis and seasonal flu? This is a hot research area and more findings will be emerging.
Vitamin D and Multiple Sclerosis: Multiple sclerosis (MS) rates are much higher far north (or far south) of the equator than in sunnier climes, and researchers suspect that chronic vitamin D deficiencies may be one reason why. One prospective study to look at this question found that among white men and women, those with the highest vitamin D blood levels had a 62 percent lower risk of developing MS than those with the lowest vitamin D levels. (39) The study didn’t find this effect among black men and women, most likely because there were fewer black study participants and most of them had low vitamin D levels, making it harder to find any link between vitamin D and MS if one exists.
Vitamin D and Type 1 Diabetes: Type 1 diabetes is another disease that varies with geography—a child in Finland is about 400 times more likely to develop it than a child in Venezuela. (40) Evidence that vitamin D may play a role in preventing type 1 diabetes comes from a 30-year study that followed more than 10,000 Finnish children from birth: Children who regularly received vitamin D supplements during infancy had a nearly 90 percent lower risk of developing type 1 diabetes than those who did not receive supplements. (41) Other European case-control studies, when analyzed together, also suggest that vitamin D may help protect against type 1 diabetes. (42) No randomized controlled trials have tested this notion, and it is not clear that they would be possible to conduct.
Vitamin D, the Flu, and the Common Cold: The flu virus wreaks the most havoc in the winter, abating in the summer months. This seasonality led a British doctor to hypothesize that a sunlight-related “seasonal stimulus” triggered influenza outbreaks. (43) More than 20 years after this initial hypothesis, several scientists published a paper suggesting that vitamin D may be the seasonal stimulus. (44) Among the evidence they cite:
- Vitamin D levels are lowest in the winter months. (44)
- The active form of vitamin D tempers the damaging inflammatory response of some white blood cells, while it also boosts immune cells’ production of microbe-fighting proteins. (44)
- Children who have vitamin D-deficiency rickets are more likely to get respiratory infections, while children exposed to sunlight seem to have fewer respiratory infections. (44)
- Adults who have low vitamin D levels are more likely to report having had a recent cough, cold, or upper respiratory tract infection. (45)
A recent randomized controlled trial in Japanese school children tested whether taking daily vitamin D supplements would prevent seasonal flu. (46) The trial followed nearly 340 children for four months during the height of the winter flu season. Half of the study participants received pills that contained 1,200 IU of vitamin D; the other half received placebo pills. Researchers found that type A influenza rates in the vitamin D group were about 40 percent lower than in the placebo group; there was no significant difference in type B influenza rates. This was a small but promising study, and more research is needed before we can definitively say that vitamin D protects against the flu. But don’t skip your flu shot, even if vitamin D has some benefit.
Vitamin D and Tuberculosis: Before the advent of antibiotics, sunlight and sun lamps were part of the standard treatment for tuberculosis (TB). (47) More recent research suggests that the “sunshine vitamin” may be linked to TB risk. Several case-control studies, when analyzed together, suggest that people diagnosed with tuberculosis have lower vitamin D levels than healthy people of similar age and other characteristics. (48) Such studies do not follow individuals over time, so they cannot tell us whether vitamin D deficiency led to the increased TB risk or whether taking vitamin D supplements would prevent TB. There are also genetic differences in the receptor that binds vitamin D, and these differences may influence TB risk. (49) Again, more research is needed. (49)
Vitamin D and Risk of Premature Death
A promising report in the Archives of Internal Medicine suggests that taking vitamin D supplements may even reduce overall mortality rates: A combined analysis of multiple studies found that taking modest levels of vitamin D supplements was associated with a statistically significant 7 percent reduction in mortality from any cause. (50) The analysis looked at the findings from 18 randomized controlled trials that enrolled a total of nearly 60,000 study participants; most of the study participants took between 400 and 800 IU of vitamin D per day for an average of five years. Keep in mind that this analysis has several limitations, chief among them the fact that the studies it included were not designed to explore mortality in general, or explore specific causes of death. More research is needed before any broad claims can be made about vitamin D and mortality. (51)
Holick MF. Vitamin D deficiency. N Engl J Med. 2007; 357:266-81.
Gordon CM, DePeter KC, Feldman HA, Grace E, Emans SJ. Prevalence of vitamin D deficiency among healthy adolescents. Arch Pediatr Adolesc Med. 2004; 158:531-7.
Lips P. Worldwide status of vitamin D nutrition. J Steroid Biochem Mol Biol. 2010; 121:297-300.
Robinson PD, Hogler W, Craig ME, et al. The re-emerging burden of rickets: a decade of experience from Sydney. Arch Dis Child. 2006; 91:564-8.
Kreiter SR, Schwartz RP, Kirkman HN, Jr., Charlton PA, Calikoglu AS, Davenport ML. Nutritional rickets in African American breast-fed infants. J Pediatr. 2000; 137:153-7.
Misra M, Pacaud D, Petryk A, Collett-Solberg PF, Kappy M. Vitamin D deficiency in children and its management: review of current knowledge and recommendations. Pediatrics. 2008; 122:398-417.
Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington, D.C.: National Academies Press, 2010.
Holick MF. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. Am J Clin Nutr. 2004; 79:362-71.
Boonen S, Lips P, Bouillon R, Bischoff-Ferrari HA, Vanderschueren D, Haentjens P. Need for additional calcium to reduce the risk of hip fracture with vitamin d supplementation: evidence from a comparative metaanalysis of randomized controlled trials. J Clin Endocrinol Metab. 2007; 92:1415-23.
Bischoff-Ferrari HA, Willett WC, Wong JB, Giovannucci E, Dietrich T, Dawson-Hughes B. Fracture prevention with vitamin D supplementation: a meta-analysis of randomized controlled trials. JAMA. 2005; 293:2257-64.
Cauley JA, Lacroix AZ, Wu L, et al. Serum 25-hydroxyvitamin D concentrations and risk for hip fractures. Ann Intern Med. 2008; 149:242-50.
Cauley JA, Parimi N, Ensrud KE, et al. Serum 25 HydroxyVitamin D and the Risk of Hip and Non-spine Fractures in Older Men. J Bone Miner Res. 2009.
Bischoff-Ferrari HA, Willett WC, Wong JB, et al. Prevention of nonvertebral fractures with oral vitamin D and dose dependency: a meta-analysis of randomized controlled trials. Arch Intern Med. 2009; 169:551-61.
Bischoff-Ferrari HA, Dawson-Hughes B, Willett WC, et al. Effect of Vitamin D on falls: a meta-analysis. JAMA. 2004; 291:1999-2006.
Broe KE, Chen TC, Weinberg J, Bischoff-Ferrari HA, Holick MF, Kiel DP. A higher dose of vitamin D reduces the risk of falls in nursing home residents: a randomized, multiple-dose study. J Am Geriatr Soc. 2007; 55:234-9.
Bischoff-Ferrari HA, Orav EJ, Dawson-Hughes B. Effect of cholecalciferol plus calcium on falling in ambulatory older men and women: a 3-year randomized controlled trial. Arch Intern Med. 2006; 166:424-30.
Bischoff-Ferrari HA, Dawson-Hughes B, Staehelin HB, et al. Fall prevention with supplemental and active forms of vitamin D: a meta-analysis of randomised controlled trials. BMJ. 2009; 339:b3692.
Sanders KM, Stuart AL, Williamson EJ; et al. Annual high-dose oral vitamin D and falls and fractures in older women: a randomized controlled trial. JAMA. 2010;303:1815-1822.
Giovannucci E. Expanding roles of vitamin D. J Clin Endocrinol Metab. 2009; 94:418-20.
Giovannucci E, Liu Y, Hollis BW, Rimm EB. 25-hydroxyvitamin D and risk of myocardial infarction in men: a prospective study. Arch Intern Med. 2008; 168:1174-80.
Pilz S, Marz W, Wellnitz B, et al. Association of vitamin D deficiency with heart failure and sudden cardiac death in a large cross-sectional study of patients referred for coronary angiography. J Clin Endocrinol Metab. 2008; 93:3927-35.
Pilz S, Dobnig H, Fischer JE, et al. Low vitamin D levels predict stroke in patients referred to coronary angiography. Stroke. 2008; 39:2611-3.
Wang TJ, Pencina MJ, Booth SL, et al. Vitamin D deficiency and risk of cardiovascular disease. Circulation. 2008; 117:503-11.
Dobnig H, Pilz S, Scharnagl H, et al. Independent association of low serum 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D levels with all-cause and cardiovascular mortality. Arch Intern Med. 2008; 168:1340-9.
Holick MF. The vitamin D deficiency pandemic and consequences for nonskeletal health: mechanisms of action. Mol Aspects Med. 2008; 29:361-8.
Garland CF, Garland FC. Do sunlight and vitamin D reduce the likelihood of colon cancer? Int J Epidemiol. 1980; 9:227-31.
Garland CF, Gorham ED, Mohr SB, Garland FC. Vitamin D for cancer prevention: global perspective. Ann Epidemiol. 2009; 19:468-83.
Yin L, Grandi N, Raum E, Haug U, Arndt V, Brenner H. Meta-analysis: longitudinal studies of serum vitamin D and colorectal cancer risk. Aliment Pharmacol Ther. 2009; 30:113-25.
Wu K, Feskanich D, Fuchs CS, Willett WC, Hollis BW, Giovannucci EL. A nested case control study of plasma 25-hydroxyvitamin D concentrations and risk of colorectal cancer. J Natl Cancer Inst. 2007; 99:1120-9.
Gorham ED, Garland CF, Garland FC, et al. Optimal vitamin D status for colorectal cancer prevention: a quantitative meta analysis. Am J Prev Med. 2007; 32:210-6.
Giovannucci E. Epidemiological evidence for vitamin D and colorectal cancer. J Bone Miner Res. 2007; 22 Suppl 2:V81-5.
Lin J, Zhang SM, Cook NR, Manson JE, Lee IM, Buring JE. Intakes of calcium and vitamin D and risk of colorectal cancer in women. Am J Epidemiol. 2005; 161:755-64.
Huncharek M, Muscat J, Kupelnick B. Colorectal cancer risk and dietary intake of calcium, vitamin D, and dairy products: a meta-analysis of 26,335 cases from 60 observational studies. Nutr Cancer. 2009; 61:47-69.
Bertone-Johnson ER, Chen WY, Holick MF, et al. Plasma 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D and risk of breast cancer. Cancer Epidemiol Biomarkers Prev. 2005; 14:1991-7.
Garland CF, Gorham ED, Mohr SB, et al. Vitamin D and prevention of breast cancer: pooled analysis. J Steroid Biochem Mol Biol. 2007; 103:708-11.
Lin J, Manson JE, Lee IM, Cook NR, Buring JE, Zhang SM. Intakes of calcium and vitamin D and breast cancer risk in women. Arch Intern Med. 2007; 167:1050-9.
Robien K, Cutler GJ, Lazovich D. Vitamin D intake and breast cancer risk in postmenopausal women: the Iowa Women’s Health Study. Cancer Causes Control. 2007; 18:775-82.
Freedman DM, Chang SC, Falk RT, et al. Serum levels of vitamin D metabolites and breast cancer risk in the prostate, lung, colorectal, and ovarian cancer screening trial. Cancer Epidemiol Biomarkers Prev. 2008; 17:889-94.
Munger KL, Levin LI, Hollis BW, Howard NS, Ascherio A. Serum 25-hydroxyvitamin D levels and risk of multiple sclerosis. JAMA. 2006; 296:2832-8.
Gillespie KM. Type 1 diabetes: pathogenesis and prevention. CMAJ. 2006; 175:165-70.
Hypponen E, Laara E, Reunanen A, Jarvelin MR, Virtanen SM. Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study. Lancet. 2001; 358:1500-3.
Zipitis CS, Akobeng AK. Vitamin D supplementation in early childhood and risk of type 1 diabetes: a systematic review and meta-analysis. Arch Dis Child. 2008; 93:512-7.
Hope-Simpson RE. The role of season in the epidemiology of influenza. J Hyg (Lond). 1981; 86:35-47.
Cannell JJ, Vieth R, Umhau JC, et al. Epidemic influenza and vitamin D. Epidemiol Infect. 2006; 134:1129-40.
Ginde AA, Mansbach JM, Camargo CA, Jr. Association between serum 25-hydroxyvitamin D level and upper respiratory tract infection in the Third National Health and Nutrition Examination Survey. Arch Intern Med. 2009; 169:384-90.
Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010 91:1255-60. Epub 2010 Mar 10.
Zasloff M. Fighting infections with vitamin D. Nat Med. 2006; 12:388-90.
Nnoaham KE, Clarke A. Low serum vitamin D levels and tuberculosis: a systematic review and meta-analysis. Int J Epidemiol. 2008; 37:113-9.
Chocano-Bedoya P, Ronnenberg AG. Vitamin D and tuberculosis. Nutr Rev. 2009; 67:289-93.
Autier P, Gandini S. Vitamin D supplementation and total mortality: a meta-analysis of randomized controlled trials. Arch Intern Med. 2007; 167:1730-7.
Giovannucci E. Can vitamin D reduce total mortality? Arch Intern Med. 2007; 167:1709-10.
Dawson-Hughes B, Mithal A, Bonjour JP, et al. IOF position statement: vitamin D recommendations for older adults. Osteoporos Int. 2010. 21:1151-4.
Canadian Cancer Society. Canadian Cancer Society Announces Vitamin D Recommendation. 2007. Accessed March 24, 2011.
National Academies. Press Release: IOM Report Sets New Dietary Intake Levels for Calcium and Vitamin D To Maintain Health and Avoid Risks Associated With Excess. November 30, 2010. Accessed March 24, 2011.
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Vitamins are substances that your body needs to grow and develop normally. Vitamin D helps your body absorb calcium. Calcium is one of the main building blocks of bone. A lack of vitamin D can lead to bone diseases such as osteoporosis or rickets. Vitamin D also has a role in your nerve, muscle, and immune systems.
You can get vitamin D in three ways: through your skin, from your diet, and from supplements. Your body forms vitamin D naturally after exposure to sunlight. However, too much sun exposure can lead to skin aging and skin cancer. So many people try to get their vitamin D from other sources.
Vitamin D-rich foods include egg yolks, saltwater fish, and liver. Some other foods, like milk and cereal, often have added vitamin D.
You can also take vitamin D supplements. Check with your health care provider to see how much you should take. People who might need extra vitamin D include
- Older adults
- Breastfed infants
- People with dark skin
- People with certain conditions, such as liver diseases, cystic fibrosis and Crohn’s disease
- People who have obesity or have had gastric bypass surgery
NIH: National Institutes of Health Office of Dietary Supplements