Side effects of calcium citrate

Calcium citrate

Generic Name: calcium citrate (KAL see um SIT rayt)
Brand Name: Citracal, Cit Calcium (obsolete), Citracal Liquitab, Calcitrate

Medically reviewed by on Dec 3, 2019 – Written by Cerner Multum

  • Overview
  • Side Effects
  • Professional
  • Interactions
  • More

What is calcium citrate?

Calcium is a mineral that is found naturally in foods. Calcium is necessary for many normal functions of the body, especially bone formation and maintenance.

Calcium citrate is used to prevent and to treat calcium deficiencies.

Calcium citrate may also be used for purposes not listed in this medication guide.

Important Information

Follow all directions on your medicine label and package. Tell each of your healthcare providers about all your medical conditions, allergies, and all medicines you use.

Before taking this medicine

Ask a doctor or pharmacist if it is safe for you to take calcium citrate if you have ever had:

  • kidney disease;

  • kidney stones;

  • cancer;

  • a parathyroid gland disorder; or

  • high levels of calcium in your blood.

Ask a doctor before using calcium citrate if you are pregnant or breast-feeding. Your dose needs may be different during pregnancy or while you are nursing.

How should I take calcium citrate?

Use exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.

You may take calcium citrate with or without food.

Swallow the tablet with a full glass of water.

Calcium citrate may be only part of a complete program of treatment that also includes dietary changes. Learn about the foods that contain calcium.

Your calcium citrate dose may need to be adjusted as you make changes to your diet. Follow your doctor’s instructions very closely.

Store at room temperature away from moisture and heat.

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while taking calcium citrate?

Ask a doctor or pharmacist before taking any multivitamins, mineral supplements, or antacids while you are taking calcium citrate.

Calcium citrate side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

  • little or no urination;

  • swelling, rapid weight gain; or

  • high levels of calcium in your blood–nausea, vomiting, constipation, increased thirst or urination, muscle weakness, bone pain, confusion, lack of energy, or feeling tired.

Common side effects may include:

  • upset stomach; or

  • constipation.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect calcium citrate?

Calcium citrate can make it harder for your body to absorb certain medicines. If you take other medications, take them at least 2 hours before or 4 to 6 hours after you take calcium citrate.

Other drugs may interact with calcium citrate, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2018 Cerner Multum, Inc. Version: 4.01.

Medical Disclaimer

More about calcium citrate

  • Side Effects
  • Drug Interactions
  • En Español
  • Drug class: minerals and electrolytes

Consumer resources

  • Calcium Citrate

Other brands: Calcitrate

Professional resources

  • Calcium Citrate (Wolters Kluwer)

Related treatment guides

  • Osteoporosis
  • Dietary Supplementation

Treatment Options for Osteoporosis

Estrogen.—Estrogen is the best current option for the prevention and treatment of osteoporosis. Numerous studies have established that, in general, estrogen increases the mean vertebral bone mass by more than 5% and decreases the rate of vertebral fractures by 50%.2x2Lufkin, EG, Wahner, HW, O’Fallon, WM, Hodgson, SF, Kotowicz, MA, Lane, AW et al. Treatment of postmeno-pausal osteoporosis with transdermal estrogen. Ann Intern Med. 1992; 117: 1–9
Crossref | PubMed | Scopus (721) | Google ScholarSee all References Estrogen can be prescribed either orally or as a transdermal patch. The most commonly used estrogen preparations in the United States are listed in Table 1Table 1.

Table 1Comparable Dosageii of Estrogen Preparations

Preparation Trade name Dosage (mg/day)
 Conjugated estrogen Premarin (Wyeth-Ayerst) 0.625
 Estropipate Ogen (Abbott) 0.75
 Ethinyl estfadiol Estinyl (Schering) 0.02
 Estradiol Estrace (Bristol-Myers Squibb) 1
Dermal patch
 Transdermal estradiol Estraderm (Ciba) 0.5 (1 patch every 3.5 days)

View Table in HTML

In addition to reducing the rate of fractures, long-term estrogen therapy may decrease the occurrence of coronary disease by as much as 50%.3x3Grady, D, Rubin, SM, Petitti, DB, Fox, CS, Black, D, Ettinger, B et al. Hormone therapy to prevent disease and prolong life in postmenopausal women. Ann Intern Med. 1992; 117: 1016–1037
Crossref | PubMed | Scopus (2094) | Google ScholarSee all References For an individual patient, the benefits of estrogen replacement therapy should be weighed against the possible risks. For women with an intact uterus, the potential increased risk of endometrial cancer is eliminated by the concurrent administration of a progestin, either cyclically (that is, medroxyprogesterone acetate, 10 mg/day for 12 to 14 days each month) or continuously (2.5 mg daily). The most controversial issue associated with estrogen therapy is the possible increase in the risk of breast cancer. A meta-analysis of the existing literature suggests that the increased risk may be 30% after estrogen therapy for 10 years or more.3x3Grady, D, Rubin, SM, Petitti, DB, Fox, CS, Black, D, Ettinger, B et al. Hormone therapy to prevent disease and prolong life in postmenopausal women. Ann Intern Med. 1992; 117: 1016–1037
Crossref | PubMed | Scopus (2094) | Google ScholarSee all References This issue is far from resolved, however, inasmuch as two recent publications reached conflicting conclusions.4x4Colditz, GA, Hankinson, SE, Hunter, DJ, Willet, WC, Manson, JE, Stampfer, MJ et al. The use of estrogens and progestins and the risk of breast cancer in postmenopausal women. N Engl J Med. 1995; 332: 1589–1593
Crossref | PubMed | Scopus (1406) | Google ScholarSee all References, 5x5Stanford, JL, Weiss, NS, Voigt, LF, Daling, JR, Habel, LA, and Rossing, MA. Combined estrogen and progestin hormone replacement therapy in relation to risk of breast cancer in middle-aged women. JAMA. 1995; 274: 137–142
Crossref | PubMed | Google ScholarSee all References In one study4x4Colditz, GA, Hankinson, SE, Hunter, DJ, Willet, WC, Manson, JE, Stampfer, MJ et al. The use of estrogens and progestins and the risk of breast cancer in postmenopausal women. N Engl J Med. 1995; 332: 1589–1593
Crossref | PubMed | Scopus (1406) | Google ScholarSee all References, an approximately 30 to 40% increase in the risk of breast cancer was found among current estrogen users, whereas in the other study,5x5Stanford, JL, Weiss, NS, Voigt, LF, Daling, JR, Habel, LA, and Rossing, MA. Combined estrogen and progestin hormone replacement therapy in relation to risk of breast cancer in middle-aged women. JAMA. 1995; 274: 137–142
Crossref | PubMed | Google ScholarSee all References no increase in the risk of breast cancer could be demonstrated. On the basis of the cumulative body of evidence, the beneficial effects of estrogen replacement for the skeleton and cardiovascular disease generally outweigh the potential risks; however, the decision about estrogen replacement therapy must be individualized.

Calcium.—Several studies indicate that calcium supplementation can retard the rate of postmenopausal bone loss,6x6Reid, IR, Ames, RW, Evans, MC, Gamble, GD, and Sharpe, SJ. Effect of calcium supplementation on bone loss in postmenopausal women. N Engl J Med. 1993; 328: 460–464
Crossref | PubMed | Scopus (426) | Google ScholarSee all References although the effect of calcium intake on the rate of fracture has not been evaluated in a controlled clinical trial. On the basis of the recent recommendations from the National Institutes of Health Consensus Development Panel, postmenopausal women should take 1,000 to 1,500 mg of calcium daily.7x7NIH Consensus Development Panel. Optimal calcium intake . JAMA. 1994; 272: 1942–1948
Crossref | PubMed | Scopus (406) | Google ScholarSee all References Several calcium preparations are available; the most commonly used are listed in Table 2Table 2. Calcium carbonate is the most widely used preparation and is generally well tolerated. In some patients, however, it can cause constipation or abdominal discomfort. In addition, calcium carbonate is poorly absorbed in the absence of stomach acid. Because a substantial percentage of postmenopausal and elderly women have relative achlorhydria and generate free stomach acid only during meals, the calcium supplement should be taken with meals. For patients with absolute achlorhydria, calcium citrate is the preferred option.

Table 2Commonly Used Calcium Preparations

Trade name Type of salt Elemental calcium per tablet (mg) Cost of 1,500 mg
(SmithKline Beecham) Carbonate 250 $0.54
Os-Cal 500 (SmithKline Beecham) Carbonate 500 0.30
Generic oyster shell calcium Carbonate 500 0.15
Turns (SmithKline Beecham) Carbonate 200 0.29
Posture (Whitehall) Phosphate 600 0.38
Citracal (Mission) Citrate 200 0.70

View Table in HTML

Vitamin D or Vitamin D Analogues.—Vitamin D is usually given with calcium therapy to increase the fractional absorption of calcium. For most patients, 400 to 800 IU of vitamin D (amounts that are in most over-the-counter multivitamin preparations) is sufficient to ensure adequate vitamin D status. In some patients, however, despite calcium and vitamin D supplementation, calcium absorption remains low. Thus, for patients with persistently low urinary calcium values of less than 100 mg/day, higher dosages of vitamin D (50,000 IU every 7 to 10 days) may be appropriate. Unfortunately, the production of vitamin D in high-dose formulations has recently been discontinued in the United States. Alternatives include a liquid preparation (Calciferol drops, Schwarz Pharma), which provides 8,000 IU/mL, and calcifediol (25-hydroxyvitamin D) (Calderol, Organon, Inc.). Fifty μg of calcifediol is approximately equivalent to 50,000 IV of vitamin D. Another alternative is calcitriol (1,25-dihydroxyvitamin D) (Rocaltrol, Roche Laboratories), which has been shown to decrease vertebral fracture rates by 50%.8x8Gallagher, JC. Metabolic effects of synthetic calcitriol (Rocaltrol) in the treatment of postmenopausal osteoporosis. Metabolism. 1990; 39: 27–29
Abstract | Full Text PDF | PubMed | Scopus (18) | Google ScholarSee all References When calcitriol is used with calcium supplementation, no more than 0.25 μg/day should be taken. With all high-dose vitamin D supplementation, monitoring of serum and urine calcium values is necessary.

Calcitonin.—Calcitonin is an option for patients in whom estrogen is contraindicated or who are unwilling to take estrogen. The disadvantages of calcitonin are the expense ($1,500 to $3,000 annually) and the requirement for parenteral administration. Intranasally administered calcitonin is available in Europe, and clinical trials with this method are under way in the United States.

Calcitonin has been shown to increase vertebral bone mass transiently in women with postmenopausal osteoporosis, particularly those with increased rates of bone turnover.9x9Civitelli, R, Gonnelli, S, Zacchei, F, Bigazzi, S, Vattimo, A, Avioli, LV et al. Bone turnover in postmenopausal osteoporosis: effect of calcitonin treatment. J Clin Invest. 1988; 82: 1268–1274
Crossref | PubMed | Scopus (298) | Google ScholarSee all References Side effects include nausea and flushing. In addition, in some patients, resistance to calcitonin may develop because of the development of neutralizing antibodies. The usual dosage is 0.5 mL (100 U) of salmon calcitonin (Calcimar, Rhône-Poulenc Rorer Pharmaceuticals, Inc., or Miacalcin, Sandoz Pharmaceuticals) daily by subcutaneous injection. Because of the possibility of inducing secondary hyperparathyroidism, calcium supplements should always be given with calcitonin.

Bisphosphonates.—Bisphosphonates, carbon-substituted analogues of pyrophosphate, are potent inhibitors of bone resorption. These drugs have the potential to become attractive alternatives to estrogen for women concerned about the side effects of estrogen. The only compound currently available is the first-generation bisphosphonate etidronate disodium (Didronel, Procter & Gamble Pharmaceuticals). Initial data indicated that intermittent use of etidronate (400 mg daily for 2 weeks followed by 11 to 13 weeks of calcium supplementation) decreased the rate of vertebral fractures.10x10Storm, T, Thamsborg, G, Steiniche, T, Genant, HK, and Sørensen, OH. Effect of intermittent cyclical etidronate therapy on bone mass and fracture rate in women with postmenopausal osteoporosis. N Engl J Med. 1990; 322: 1265–1271
Crossref | PubMed | Scopus (821) | Google ScholarSee all References, 11x11Watts, NB, Harris, ST, Genant, HK, Wasnich, RD, Miller, PD, Jackson, RD et al. Intermittent cyclical etidronate treatment of postmenopausal osteoporosis. N Engl J Med. 1990; 323: 73–79
Crossref | PubMed | Scopus (860) | Google ScholarSee all References This decrease was not confirmed, however, by further follow-up. Because of the possibility of therapeutic doses of etidronate impairing mineralization and the long retention of bisphosphonates in bone, a concern is that etidronate could have adverse long-term effects such as increasing the incidence of hip fracture. In comparison to etidronate, second- and third-generation bisphosphonates such as tiludronate, alendronate, and risedronate are much more potent and have a greater therapeutic window between inhibition of bone resorption and inhibition of mineralization. These drugs are currently being used in clinical trials and may soon be approved by the Food and Drug Administration for use in the management of osteoporosis.

Estrogen Analogues.—Tamoxifen citrate, a benzodiazepine-derived drug, is an antiestrogen for breast tissue but seems to have an estrogen-agonist effect on bone tissue.12x12Love, RR, Mazess, RB, Barden, HS, Epstein, S, Newcomb, PA, Jordan, VC et al. Effects of tamoxifen on bone mineral density in postmenopausal women with breast cancer. N Engl J Med. 1992; 326: 852–856
Crossref | PubMed | Scopus (942) | Google ScholarSee all References The use of tamoxifen is limited, however, because of its side effects, including a partial agonist effect on the uterus. Raloxifene, another estrogen analogue, seems to have estrogen-agonistic effects on bone and antiestrogenic effects on breast and uterine tissue.13x13Black, LJ, Sato, M, Rowley, ER, Magee, DE, Bekele, A, Williams, DC et al. Raloxifene (LY139481 HCI) prevents bone loss and reduces serum cholesterol without causing uterine hypertrophy in ovariectomized rats. J Clin Invest. 1994; 93: 63–69
Crossref | PubMed | Scopus (565) | Google ScholarSee all References Thus, it could be given without a progestin and may become a useful alternative to estrogen in the management of osteoporosis.

Individuals reach peak bone mass around their early 20s, after which bone mass is lost faster than it is created.1 Thus, as an individual ages, the risk for osteoporosis increases. If age is a nonmodifiable risk factor, what can an individual do to prevent osteoporosis?
In addition to doing weight-bearing exercises or muscle-strengthening exercises to build and maintain bone density, it’s important to get enough calcium and vitamin D.
I’ve filled a lot of calcium with vitamin D supplements for elderly patients. A couple of weeks ago, I encountered a prescription for a calcium supplement and a prescription for a constipation medication. One of the adverse effects of calcium supplements is constipation, so I instantly knew that the calcium supplement was most likely causing the constipation.
In pharmacy school, I was taught to see if there was a cause when I learned of a patient’s adverse reaction, because if I’m treating the problem without removing the cause, the problem will still persist. In this situation, I couldn’t remove the cause. If I were to request that the doctor stop prescribing the calcium supplements, the elderly patient would be at higher risk for osteoporosis. If I can’t remove the cause, what can I do in this type of situation?
Although calcium carbonate is the cheapest calcium supplement option, it’s also the most constipating.2 If cost is an issue, I could recommend that the patient try a few different brands; if cost isn’t an issue, I could recommend that the patient try a few different types of calcium supplements to find which one the patient tolerates best.2 I could show the patient how to read the label to determine which has lower calcium per dose, as lower dose calcium supplements may be better tolerated.3 Although this may mean being dosed more than one time per day to achieve the prescribed dosage, spreading out the calcium doses throughout the day may mean better tolerance.4 Taking the supplements with meals may also help.4 Many patients taking calcium supplements are over age 50 and may be taking acid blockers such as Zantac (ranitidine), Protonix (pantoprazole), or Prilosec (omeprazole). These patients have low stomach acid, which is an issue for calcium carbonate because it relies on stomach acid for absorption. Although not the cheapest calcium supplement option, calcium citrate is recommended for these patients.
Patients can benefit from nonpharmacological advice. Regardless of which calcium supplement the patient is taking, there may still be the possibility of constipation. Patients should be counseled to drink plenty of water, increase their dietary fiber intake, and be physically active to minimize this possibility.3

1. Osteoporosis. Mayo Clinic website. Accessed November 16, 2016.
2. Nutrition and healthy eating. Mayo Clinic website. Accessed November 16, 2016.
3. All about calcium supplements. New York State Department of Health website. Accessed November 16, 2016.
4. National Institutes of Health. Calcium: dietary supplement fact sheet. NIH website. Accessed November 16, 2016.

How Much Should You Take?

It depends on how much you’re already getting in your diet. Adults need 1,000 milligrams of calcium (from all sources) every day, and that amount goes up with age. Women over 50 and men over 70 need 1,200 milligrams per day. If you think you need a supplement to boost your number, check with your doctor.

The more calcium you take at one time, the harder it is for your body to process it. Aim for 500 milligrams or less. You may want to take a smaller amount at each meal throughout the day to add up to your total.

More than the recommended daily amount isn’t good for you. It may even be harmful, according to a 2011 study in The Journal of Clinical Endocrinology and Metabolism.

Your body gets rid of extra calcium through your kidneys, and it goes into your urine, raising the risk of kidney stones for some people. High levels of the mineral in your blood can lead to kidney problems, as well as hardened blood vessels and tissue. Some studies also link high calcium intake, particularly from supplements, with a greater risk of heart disease, though the results aren’t settled.

All About Calcium Supplements

Anne Chiavacci, RD, MS, MA Brigham and Women’s Hospital
Previously published on

Calcium is well known for its role in building and maintaining strong bones and teeth. It also functions in blood clotting, nerve conduction and muscle contraction. There is preliminary evidence that calcium supplements may decrease blood pressure, colon cancer risk, and symptoms of PMS.

It is best to try to meet calcium needs with food sources. For those who find it difficult, calcium supplements are helpful, but not all supplements are equal. The following are some of the most common questions nutritionists are asked about calcium supplementation, and our answers.

How much calcium do I need?

How much calcium you need depends on your age and whether you are pregnant or breast feeding.

Group Milligrams Per Day
1 – 3 years 500 mg
4 – 8 years 800 mg
9 – 18 years 1,300 mg
19 – 50 years 1,000 mg
51+ years 1,200 mg
Pregnancy and breast feeding 1,000 – 3,000 mg

Which foods contain calcium?

Calcium can be found in many foods, not only in dairy products.

How do I choose a calcium supplement?

Calcium carbonate and calcium citrate are the optimal forms of supplement.

  • Calcium carbonate supplements
    • Viactiv Soft Calcium Chews with vitamins D & K
    • Tums 500
    • Caltrate 600
    • GNC Calcium Complete (400 mg)
    • Os-Cal 500
  • Calcium citrate supplements
    • Citracal
    • Citracal with vitamin D (315 mg)
    • TwinLab Calcium Citrate Caps (300 mg)
    • Some calcium-fortified orange juice (but not all)
    • GNC Calcimate Plus 800 (calcium citrate malate)
    • Solgar Calcium Citrate (250 mg)
    • Citracal Ultradense Calcium Citrate Tablets (200 mg)

Calcium carbonate should be taken with meals because it requires stomach acid to dissolve and absorb. Calcium carbonate has the most calcium per pill (40 percent), therefore fewer pills are needed. Some find calcium carbonate constipating.

Calcium citrate is well absorbed on an empty stomach and does not constipate. The downside is that it has less calcium per pill (20 percent). On the positive side, calcium citrate is less dependent on stomach acid for absorption. Older people often have decreased stomach acid, so the citrate form may be a better choice than calcium carbonate.

Avoid supplements made of dolomite, oyster shell and bone meal which may contain metals and lead. Calcium phosphate, calcium lactate and calcium gluconate are not recommended because they have very small amounts of calcium.

Don’t be fooled by ads for coral calcium promoting it as a cure for around 200 diseases including heart disease, cancer and diabetes. Coral calcium is merely calcium carbonate. In June 2003, the U.S. Federal Trade Commission charged marketers with making false claims about the product’s health benefits.

What is the difference between total calcium and elemental calcium?

The amount of elemental calcium is the number to use. During digestion, the elemental calcium is released from the compound (carbonate, citrate) and becomes available for absorption. Calcium carbonate provides 40 percent elemental calcium; the other 60 percent is the carbonate ingredient. Therefore, 600 milligrams (mg) of calcium carbonate provides 240 mg elemental calcium. Calcium citrate is 20 percent elemental calcium; 600 mg of calcium citrate provides 120 mg elemental calcium. The number that is part of the brandname (such as Caltrate 600, Os-Cal 500 and TUMS 500 Extra Strength) usually indicates the amount of elemental calcium in each tablet or pill. But you should read the label to be certain.

A USP (United States Pharmacopeia) symbol on the label means that the calcium supplement is free of lead and other metals. It also meets standards for quantity of elemental calcium in the tablet and how well it dissolves. The application for this symbol is voluntary, so a product may be acceptable even if it does not display this symbol. Test your supplement by putting it in a glass of clear vinegar. Stir occasionally. If it dissolves within 30 minutes, it should do so in your stomach too!

What increases or decreases calcium absorption?

Spread out your calcium from foods and supplements throughout the day. For best absorption, take no more than 500 mg calcium at one time. (To avoid calcium toxicity, do not exceed 2,500 mg of elemental calcium per day.)

Vitamin D enhances calcium absorption, so make sure to get 400 to 800 international units (IU) of vitamin D per day.

Oxalic acid found in dark leafy greens, rhubarb, soy and cocoa decreases the absorption of calcium in these foods. Foods high in insoluble fiber (such as whole grains and wheat bran) also can decrease the absorption of calcium taken at the same time.

Phosphoric acid in dark sodas can interfere with your body’s absorption of calcium. Prolonged use of magnesium-containing laxatives compromises calcium absorption as well.

Here are some other factors to consider:

  • Caffeine increases calcium lost in the urine. Limit yourself to one to two cups of caffeinated coffee or soda per day.
  • Excess sodium in the diet also increases calcium excretion. Every 500 mg of sodium over 2,400 mg per day causes the body to excrete 10 mg of calcium.
  • Taking calcium supplements with iron or zinc compromises the absorption of these minerals.
  • Calcium decreases the absorption of certain drugs (bisphosphonates, thyroid, some antibiotics). Other drugs can increase calcium needs (corticosteroids, some diuretics).

The Bottom Line

Calcium is needed for healthy bones, teeth nails and muscle tissue. It also assists in blood clotting and heart and nerve functions. Calcium can be obtained through diet (food sources) or through supplements. It is important to review your medications with your doctor, pharmacist, or nutritionist before starting a calcium supplement.

Are calcium pills any good at preventing bone fractures?

“Calcium supplements don’t work, say experts,” The Daily Telegraph reports.

While this headline is not strictly true, new research has shown that for most healthy people, calcium supplements will make little difference to your bone health or risk of breaking a bone.

The researchers looked at the best studies they could find that had looked at the relationship between calcium and bone fracture.

For many years, older people have been advised to increase their dietary calcium intake or take a calcium supplement, as calcium is a building block of strong bones. Vitamin D is often recommended alongside calcium, as the body can’t absorb calcium without vitamin D.

However, the researchers found that increasing calcium to the high levels recommended in some countries (although not the UK) did not make much difference to the chances of breaking a bone, even when taken alongside vitamin D.

Calcium pills did increase bone strength by about one to two per cent, but the researchers say this is unlikely to make a difference to fracture risk.

Previous studies have shown that calcium supplements may cause side effects, including constipation.

However, there’s no need to stop taking calcium and vitamin D supplements if you’ve been advised to take them by your doctor, as there is little doubt they can help people who are deficient in these nutrients. As for everyone else, it seems that taking these pills is an unnecessary expense.

Where did the story come from?

Both studies were carried out in New Zealand by researchers from the University of Auckland and the University of Otago – plus researchers from the Starship Hospital involved in the bone density study. They were funded by the Health Research Council of New Zealand.

The studies were published in the peer-reviewed British Medical Journal (BMJ) on an open-access basis, so are free to view online.

The main messages of the studies came across in the media reports, although they did not go into detail about the different findings for supplements and dietary calcium, or the problems with some of the studies.

The Mail Online focused on the potential harms of calcium supplements, such as stomach upsets and heart problems, which were not included in this research.

What kind of research was this?

The researchers carried out two systematic reviews. The first looked at the effect of increased calcium on people’s bone strength, the second looked at the effect of increased calcium on people’s risk of having a fracture.

Systematic reviews are the best way of summarising the evidence on a topic at any one time. However, the results are only as good as the trials done so far.

What did the research involve?

Researchers searched for all the good quality studies they could find that looked at calcium intake and subsequent fracture or bone strength in people over 50.

Where possible, the researchers pooled the results to get an overall answer to the question of whether increasing calcium intake, from pills or food, had an effect on either fracture or bone strength.

The researchers began by looking at randomised controlled trials (RCTs) of increased dietary calcium or calcium supplements (including studies with calcium plus vitamin D). They did not find enough RCTs looking at the effects of dietary calcium on fracture to answer the question, so they also included cohort studies exploring this relationship.

The researchers pooled all the results from RCTs to give an overall figure for the effect of calcium on bone strength, measured as bone mineral density (BMD) and the chances of having any fracture, or a specific fracture of the wrist, hip or spine. They then looked at the range of results to see whether they showed the sort of spread you would expect to see by random chance.

For the cohort studies, the researchers found that the studies didn’t report their results in a consistent way. This meant they could not combine the figures in one pooled analysis. Instead, they looked at how many studies reported any effect of increased calcium intake on fracture risk.

What were the basic results?

The researchers found 59 RCTs looking at the effect of calcium on bone mineral density, including 13,790 people. The effect of increased calcium after one year was a 0.6% to 1% increase in BMD.

When they looked at the effects of eating more calcium in the diet, the researchers found 14 out of 22 cohort studies (covering 291,273 people) did not show that calcium had any effect on the chances of breaking any bone. Of those studies that found people with a higher intake of calcium were less likely to have had a fracture, most showed only a small effect.

The 26 RCTs of calcium supplements, which covered 69,107 people, showed a small effect. They appeared to reduce the risk of fractures by 11% (relative risk 0.89, 95% confidence interval 0.81 to 0.96).

However, when they looked at the overall range of results, the researchers said there were more positive results from small studies than you would expect to see by chance. They say this shows evidence of “publication bias”, where only positive studies are published and studies with negative outcomes aren’t.

They looked at the results again, including only the bigger, more reliable studies. This analysis did not show an overall protective effect from calcium supplements.

Only in one big study of frail elderly women living in nursing homes, who had very low levels of calcium and vitamin D at the outset, did supplements make a difference to the risk of hip fracture.

How did the researchers interpret the results?

The researchers say their results show that increasing calcium in the diet is not likely to decrease risk of broken bones, on current evidence.

They say the benefits found from calcium supplements are small and inconsistent, and “probably have an unfavourable risk benefit profile” given the known side effects of taking calcium.

Talking about the one study that showed a significant reduction in hip fracture, the researchers say this group of elderly women were known to have been deficient in vitamin D, and therefore to have been at higher risk of breaking bones.

They said this study should not be included in the same analyses as other studies of generally healthy people living in the community, nor should it be used to come up with calcium recommendations for the general population.


These two studies pour cold water on the idea that most healthy people aged over 50 need to eat more calcium than they currently do, or that they need to take calcium supplements. They found that, for most people, increased calcium has little effect on bone strength or chances of breaking a bone.

However, the research is based on available studies, of which there were only two small randomised controlled trials with a combined total of 262 people that looked at calcium intake and risk of fracture.

The cohort studies found are not able to show cause and effect as they are subject to confounding, so the combination of these limitations reduces the strength of the results found in this systematic review.

The UK government currently recommends getting 700mg of calcium daily – and says a healthy, varied diet is likely to provide this for most people.

Good sources of dietary calcium include dairy products such as milk, cheese and yoghurt; oily fish such as sardines and anchovies; or nuts and seeds such as almonds and sesame seeds. To get higher levels of calcium, recommended by some organisations, calcium supplements may be needed.

The results of this study suggest most people are unlikely to benefit from taking additional calcium.

We know from previous studies that calcium supplements can have side effects in some people, including constipation and kidney stones. Calcium supplements have also been linked to an increased chance of having a heart attack. You are unlikely to get these side effects from eating a normal amount of calcium as part of a healthy diet.

It’s important to remember that most of these studies were looking at generally healthy older people, not people who had a medical reason for taking calcium supplements.

If you’ve been advised by your doctor to take calcium and vitamin D supplements because you have weak bones (osteoporosis), or because you are deficient in these nutrients, you should continue to take them.

Analysis by Bazian
Edited by NHS Website

Links to the headlines

How calcium tablets can do more harm than good: Pills can increase risk of stomach upsets and heart problems while not cutting the risk of broken bones

Mail Online, 29 September 2015

Calcium supplements don’t work, say experts

The Daily Telegraph, 29 September 2015

Links to the science

Bolland MJ, et al.

Calcium intake and risk of fracture: systematic review

BMJ. Published September 29 2015

Tai V, et al.

Calcium intake and bone mineral density: systematic review and meta-analysis

BMJ. Published September 29 2015

Further reading

Michaëlsson K.

Calcium supplements do not prevent fractures

BMJ. Published September 29 2015

About the author

Leave a Reply

Your email address will not be published. Required fields are marked *