Flavonoids supplements side effects

Vitamin C and bioflavonoids: Powerful eye antioxidants

Eye Nutrition

By Gary Heiting, OD

Vitamin C and bioflavonoids are important

that help keep your eyes and body healthy. Foods high in vitamin C, such as citrus fruits and many vegetables, are also excellent sources of bioflavonoids.

Research suggests vitamin C and bioflavonoids have a complementary effect, making them both more effective when ingested together rather than separately.

Vitamin C And Your Eyes

Vitamin C (also known as ascorbic acid) is a water-soluble vitamin and a powerful antioxidant. Abundant in fruits and vegetables, vitamin C helps the body form and maintain connective tissue, including collagen found in the cornea of the eye.

Want more vitamin C in your diet? Sweet red peppers have more than three times the vitamin C of orange juice.

Vitamin C also promotes healthy bones, skin and blood vessels, including the delicate capillaries in the retina. Studies suggest long-term consumption of vitamin C also may reduce the risk of forming a cataract and vision loss from macular degeneration.

Unlike most animals, humans are unable to produce vitamin C in the body. So we must get our daily dose of ascorbic acid from our diet. A diet deficient in vitamin C can lead to scurvy — a serious disease characterized by muscle weakness, swollen and bleeding gums, loss of teeth, bleeding under the skin, soreness and stiffness of the joints, anemia, fatigue and depression.

So how much vitamin C do you need? According to the National Institutes of Health, the Recommended Dietary Allowance (RDA) of vitamin C is 90 milligrams (mg) per day for men and 75 mg for women. (Women who are pregnant or breast-feeding should take up to 120 mg per day.) Research suggests smokers need more vitamin C than nonsmokers.

Many researchers, however, feel you should consume significantly more vitamin C than the RDA. For example, 500 mg was the daily dose of vitamin C used in studies that showed a reduced risk of cataracts. And long-term studies have found that people who take more than 700 mg of supplemental vitamin C per day have a 25 percent lower risk of coronary heart disease than those who don’t take vitamin C supplements.

Because it is water-soluble, vitamin C is generally considered safe at high doses. Excess vitamin C is excreted in urine. However, doses greater than 2,000 mg per day may cause nausea and diarrhea, as well as increase the risk of kidney stones.

Excellent natural sources of vitamin C include peppers, citrus fruits, berries, tropical fruits, potatoes, tomatoes and green leafy vegetables. Foods with the highest content of vitamin C are:

  • Sweet red peppers (283 mg per one cup serving)
  • Sweet green peppers (133 mg per one cup serving)
  • Strawberries (86 mg per one cup serving)
  • Broccoli (82 mg per one cup serving)
  • Orange juice (75 mg per one cup serving)

The above values are for fresh, raw foods. Cooking and canning foods can decrease their vitamin C content. Light also destroys vitamin C. So if you drink orange juice, it’s best to purchase it in opaque containers.

Smoking, oral contraceptives, estrogen, the antibiotic tetracycline and barbiturates may decrease the effectiveness of vitamin C.

Bioflavonoids: Vitamin C’s Eye Health Partner

Bioflavonoids are a large family of substances found in most of the same foods that are good sources of vitamin C. In fact, researchers have identified more than 8,000 naturally occurring bioflavonoid structures. Bioflavonoids (also called flavonoids) are the natural pigments that give fruits and vegetables their color.

Sometimes bioflavonoids are referred to as “vitamin P,” but it has not been proven that these substance meet the requirements to be called a vitamin. Vitamins are organic compounds that are essential for normal growth and nutrition and are required in the diet because they cannot be synthesized by the body. It has not been proven that all bioflavonoids are essential to human health.

Studies of specific bioflavonoids, however, have revealed health benefits. Quercetin, for example, appears to stabilize the membranes of cells that release

, a compound involved in allergic and inflammatory reactions. Found in buckwheat and citrus fruits, quercetin may help prevent seasonal allergies.

Rutin, another bioflavonoid, may be useful for the prevention of easy bruising and other bleeding abnormalities. Rutin is found in buckwheat, capers and other plants.

And recent research suggests apigenin — a bioflavonoid found in celery, parsley, red wine, tomato sauce and other plant-based foods — may reduce the risk of ovarian cancer.

Bioflavonoids and vitamin C appear to work together in the body. Researchers believe benefits credited solely to vitamin C in the past actually may be due to the combined action of vitamin C and specific bioflavonoids. Some of these combined effects include:

  • Reduced risk of heart disease
  • Reduced risk of certain cancers
  • Certain anti-aging effects
  • Protection against infections
  • Strengthened walls of blood vessels
  • Improved blood circulation
  • Decreased blood cholesterol
  • Improved liver function

Almost any food containing vitamin C also contains bioflavonoids.

Bilberry, a plant closely related to the blueberry, is the source of bioflavonoids often touted as being good for your eyes. Bilberries are also called huckleberries or whortleberries in some regions.

Bilberries and blueberries both contain high amounts of anthocyanins — flavonoid pigments that are powerful antioxidants. Anthocyanins may help reduce the risk of cataracts and macular degeneration and help maintain the health of the cornea and blood vessels in various parts of the eye.

Researchers also are investigating other potential eye benefits of anthocyanins, including the possibility these and other bioflavonoids may help reduce inflammatory eye disease and diabetic retinopathy.

In addition to bilberries and blueberries, other good sources of anthocyanins include acai fruit, cherries, plums, cranberries, raspberries, eggplant, red and purple grapes and red wine.

Like vitamin C, bioflavonoids are water-soluble and nontoxic, even at high doses. No RDA has been established for bioflavonoids at this time.

Page updated August 2016

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Gary Heiting, OD

Gary Heiting, OD, is a former senior editor of AllAboutVision.com. Dr. Heiting has more than 30 years of experience as an eye care provider, health educator and consultant to the eyewear … read more

Notes and References

Antioxidant supplements to prevent or slow down the progression of AMD: a systematic review and meta-analysis. Eye. June 2008.

Anthocyanins and anthocyanin-rich extracts: role in diabetes and eye function. Asia Pacific Journal of Clinical Nutrition. June 2007.

Nutritional antioxidants and age related cataract and maculopathy. Experimental Eye Research. February 2007.

Antioxidant vitamins and coronary heart disease risk: a pooled analysis of 9 cohorts. American Journal of Clinical Nutrition. June 2004.

National Agriculture Library, U.S. Dept. of Agriculture

(ascorbic acid)

Vitamin C must be obtained either through diet or supplementation as unlike most animals and plants, humans have lost the ability to synthesize this nutrient. Vitamin C is water-soluble which means that only a certain amount is used and can’t be stored. Given that any excess is excreted, continually restoring vitamin C is required to ensure adequate intake.

Vitamin C is an essential component of collagen, the most abundant protein in the body that is essential for building new bone, cartilage, tendon, skin and other connective tissue. As a result, vitamin C plays an important role in wound healing by supporting the development of new tissue and blood vessels.

Vitamin C works as an antioxidant to quench free-radicals in the aqueous or watery part of cells. It also regenerates other antioxidants and works in concert with vitamin E (which works in lipid environments).

Vitamin C may play a role in the prevention and treatment of cancer, cardiovascular disease, age-related macular degeneration (AMD) and cataracts and the common cold. Epidemiological studies suggest that high intakes of fruits and vegetables are associated with lower risk of most types of cancer and reduced risk of cardiovascular disease. However, the evidence is inconsistent whether dietary vitamin C intake affects cancer risk or reduces cardiovascular disease morbidity or mortality. Studies indicate that vitamin C may slow the progression of AMD and higher intakes may reduce the risk of developing cataracts.

Under certain conditions, the requirement for vitamin C is increased. Smokers, those exposed to second hand smoke, older persons and those under stress have a greater need for this vitamin.

Major Functions of Vitamin C

– An antioxidant needed for tissue growth and repair, adrenal gland function and healthy gums

– Plays a primary role in the formation of collagen

– Promotes the healing of wounds, protects against blood clotting and bruising

– Involved in immune health

– Enhances body’s absorption of iron


Any food that contains vitamin C also contains bioflavonoids. Bioflavonoids are required for absorption of vitamin C and both work together in the body. Although bioflavonoids are not considered a vitamin, they are sometimes referred to as vitamin P.

Bioflavonoids are found abundant in citrus fruit rinds and pulp. Common bioflavonoids include citrus flavonoids found in citrus fruits; rutin in buckwheat; epigallocatechin gallate (EGCG) in green tea; anthocyanidins in bilberry; naringenin in grapefruit; oligomeric proanthocyanidins in grape seeds and skins and quercetin in onions, tea, and apples.

Food Sources

Fruits and vegetables are the best sources of vitamin C. With 2,000 mg/100 grams, rose hips have one of the highest concentrations of vitamin C. Other plants that are good sources include peppers (red pepper, hot chillis); berries (black currant, loganberry, elderberry, goji, cloudberry, strawberry, raspberry, blackberry, cranberry); citrus fruits (orange, lemon, grapefruit, tangerine, lime); green vegetables (parsley, broccoli, Brussels sprouts, kale, spinach) and other fruits (guava, kiwifruit, papaya, melon).

The vitamin C content of foods is reduced with cooking, freezing and then unthawing. Higher temperatures and longer cooking times magnify this effect. Fresh cut fruits do not lose significant vitamin content when stored in the refrigerator for a few days. Eating fruits and vegetables at their peak ripeness in their raw state is the best way to maximize vitamin C intake.

Recommended Dietary Allowance

The Recommended Dietary Allowance (RDA) for vitamin C for adult men is 90 mg and for adult women is 75 mg. Vitamin C has low toxicity and is not believed to cause serious adverse effects even at high intakes. For adults, the Tolerable Upper Intake Level for vitamin C is 2,000 mg. An RDA does not exist for bioflavonoids.

If you look on a nutritional supplement facts panel, you’ll notice the Amount Per Serving for vitamin C and the % Daily Values is at located at the top of the panel. The Amount Per Serving is based on the Reference Daily Intake (RDI) for this nutrient which is considered to be sufficient to meet the requirements of nearly all (97–98%) healthy individuals in each life-stage and sex group. The Reference Daily Intake for vitamin C is 60 mg which represents 100% of the Daily Values.

Keep in mind, that the Daily Values is the amount considered sufficient to prevent disease (e.g., scurvy which was prevalent amongst sailors up until the 18th century). Many studies indicate that higher amounts of vitamin C are required to enhance immunity and provide other health benefits.

The amount of vitamin C in the body tissues is tightly controlled. At moderate intakes (30 – 180 mg a day), 70 to 90 percent of vitamin C is absorbed. But, at doses above 1 gram, absorption falls to less than 50 percent. For this reason, taking reasonable amounts of vitamin C (150 mg) in divided doses ensures optimal absorption of this nutrient.


Certain drugs can reduce the body’s supply of vitamin C including birth control pills, non-steroidal anti-inflammatory drugs (e.g., Advil), corticosteroids, sulfa drugs and barbiturates.

VitaMedica Products

Given the role of vitamin C in developing new tissue and wound healing, it’s not surprising that this nutrient is featured in our Recovery Product line. Both the Recovery Support Program and Clinical Support Program are formulated with 750 mg of vitamin C. To optimize absorption, 375 mg is provided in both the morning and evening formulation. Additionally, these products are formulated with 600 mg of bioflavonoids to enhance absorption and assimilation of this nutrient.

Compared with our everyday supplements, the amount of vitamin C and bioflavonoids is higher in our Recovery products. That’s because the body’s requirements for these nutrients is much higher following the stress of surgery, the level of oxidation generated by anesthesia & narcotics and the importance to building new tissue.

Many of our Wellness Products are formulated with vitamin C at reasonable amounts, in divided doses. As an example, our Multi-Vitamin & Mineral and Anti-Aging Formula provide 300 mg daily of vitamin C, divided in a 150 mg morning and 150 mg evening dose. These products are also formulated with bioflavonoids to enhance absorption.

Last updated July 1, 2018

David H. Rahm, M.D. is the founder and medical director of The Wellness Center, a medical clinic located in Long Beach, CA. Dr. Rahm is also president and medical director of VitaMedica. Dr. Rahm is one of a select group of conventional medical doctors who have education and expertise in functional medicine and nutritional science. Over the past 20 years, Dr. Rahm has published articles in the plastic surgery literature and educated physicians about the importance of good peri-operative nutrition.

Citrus Bioflavonoids: Synergy with Vitamin C & Beyond

Bioflavonoids naturally extracted from citrus fruits constitute an important group of antioxidants. The major bioflavonoids found in citrus fruits are diosmin, diosmetin, hesperidin, hesperetin, naringin, naringenin, narirutin, neohesperidin, nobiletin, tangeretin, eriodictyol, and eriocitrin. In the 1950s, the nutritional benefits of bioflavonoids were so highly recognized that this group of compounds was referred to collectively as Vitamin P. While not strictly vitamins, bioflavonoids do possess “vitamin-like” properties.
The antioxidant properties of flavonoids have been recognized for more than 40 years. Increasing intake of bioflavonoids helps prevent free radicals from causing harm in the body. Citrus bioflavonoids support balanced immune cell activity for better immune response, and support for respiratory health. They also have a synergistic function with vitamin C for enhanced immune support, and have been shown to increase absorption of vitamin C. The antioxidant and anti-inflammatory benefits of citrus bioflavonoids have been shown to support metabolic, circulatory, cognitive, and joint health.
Quality and efficacy are better validated in citrus bioflavonoids that are tested for total bioflavonoid content by HPLC as well as ORACFN value, measuring specific antioxidant activity against the most influential free radicals naturally found in the human body.
Citrus Bioflavonoid Science
Citrus bioflavonoids have been evaluated and validated in numerous scientific studies. One recent study published in Critical Reviews in Food Science and Nutrition demonstrated favorable outcomes in the anti-inflammatory, antioxidant, lipid-lowering, and insulin-sensitizing properties of the bioflavonoid hesperidin.
A study published in Mediators of Inflammation suggested the bioflavonoid hesperidin may have therapeutic effect on allergic asthma. It demonstrated profound inhibitory effects on airway inflammation in a mouse model of asthma.
Another study published in Advances in Nutrition examined the biologic activities of citrus bioflavonoids, particularly on lipid metabolism in obesity, oxidative stress, and inflammation in context of metabolic syndrome. In particular, it showed the citrus bioflavonoid naringin displayed strong anti-inflammatory and antioxidant activities.
Versatility in Applications
Citrus bioflavonoids have been shown to act synergistically with vitamin C in neutralizing free radicals. They are ideal for applications targeting support for the immune system, respiratory health, cognitive health, vascular integrity, metabolism, cholesterol, joint health, and systemic antioxidant support. Citrus bioflavonoids are versatile, making them excellent ingredients for food, beverage, and dietary supplement applications. They may be used in a variety of beverages, as they are suspendable in liquids. Citrus bioflavonoids also act as natural preservatives, another benefit for food and beverage products; they also provide bitter and sour taste notes for some specialty beverages, including beer.
Innovation & Standardization
Many bioflavonoids are sourced solely from oranges, but there are many other options. Drawing from a larger selection of citrus provides more opportunity for customization. Bioflavonoids sourced from orange, lemon, lime, tangerine, and grapefruit provide the broadest bioflavonoid profiles. Each one provides its own unique profile, creating more opportunities for customized formulations. The ability to extract very specific bioflavonoids in their purest form is made possible through advanced production methods and extraction technologies.
Standardization of extracts is also important. Standardized bioflavonoid ingredients ensure consistency and quality in every batch. Today, there are options for customer-specific formulations, made possible through advances in the variety of citrus complexes and purified extracts available.

Ingredients by Nature (IBN) was originally founded as Brewster Nutrition in 1932 with a focus on R&D and science-based ingredients. Brewster pioneered advances in citrus bioflavonoids and concentrated citrus extracts. With over 80 years of experience, Brewster Nutrition and its marketing arm, IBN, now produce over 300 botanical ingredients of quality and value-added solutions for condition-specific formula applications. IBN continues to put science behind its ingredients. For more information: www.ingredientsbynature.com.

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