- Note: This information applies to adults. Children should not be given any medications or supplements not recommended by their doctor, and should take all medications recommended by their doctor. The main purpose of the article is to separate vitamin myth from fact, not to give medical advice.
Vitamin supplements are vitamins sold with specific health claims beyond their usual physiologic function. Vitamins are micronutrients which are required in very small amounts for specific physiologic processes. Since their discovery, there has been great interest in using vitamins not just to treat deficiency diseases but also for medicinal purposes. Like everything else in natural/holistic health, the claims run the gambit in factual, scientific efficacy. A few claims are backed by scientific study, most claims have been simple salesmanship, and a few have been irresponsibly, dangerously extravagant.
The dietary supplement industry is quite large, and the biggest part of the industry is vitamin sales. Numbers are difficult to come by, as they are compiled and sold by marketing firms, but best estimates place sales at over five billion dollars annually. There is much misinformation about the benefits of vitamins. This article will strive to help people make better decisions about vitamin supplementation, and help to sort out extravagant claims made by producers and marketers of vitamins.
Because of the great interest in vitamins as medications, a great deal of research has gone into investigating their safety and efficacy. However, in the US, vitamins are regulated as dietary supplements, not medications, and there are no requirement for manufacturers to prove efficacy. By definition, vitamins are needed for health. In most cases, a basic, inexpensive, "general multi-vitamin supplement" is sufficient for adults to remain healthy. However, they are often marketed for uses beyond their basic function, and in much higher doses than typically needed.
Efficacy and Safety
Vitamin A deficiencies can occur in developing nations and can lead to severe visual problems, and other conditions. Beta-carotene, a common precursor to Vitamin A used as a supplement, has been studied as an "anti-oxidant" and cancer preventative. However, large, well-conducted studies have shown an increase in lung cancer in people taking these supplements. Smokers, and others at increased risk for lung cancer, saw their risk increase even more. Also, a recent study showed an increase in aggressive prostate cancers in men taking beta carotene.
Since Vitamin A derives from beta carotene, a carotenoid pigment, massive overdoses of either substances can turn the consumer's skin yellow or orange. Also, both substances are closely related to retinoid pigments such as form the photosensitive component of most animal eyes. Such substances are also used in medicine to treat severe skin diseases such as disfiguring acne and ichthyosis; however, they can be teratogens due to their effect on DNA, requiring careful monitoring, especially in female patients.
- Vitamin B9, more commonly known as "folic acid," has been shown in several large well-controlled studies in the U.S. and China to prevent neural tube defects like spina bifida. The effect was greatest when women began taking folic acid before becoming pregnant. This has led to folate supplementation of foods in the U.S. High homocysteine levels in adults is associated with heart disease, and can be reduced by adequate folate intake, although it has not been shown that taking folic acid reduces cardiac risk.
- Vitamin B12 deficiency, usually from certain intestinal diseases or pernicious anemia is fairly rare, and when it exists, it must be treated. Supplementing this vitamin in non-deficient people has not shown to have any benefit, but oral supplementation as part of a daily multivitamin may have a small effect of reducing cardiac risk in some people.
- Folate, B12, and B6 are sometimes recommended for memory, but studies have failed to show any benefit in non-deficient individuals.
- Vitamin B6 very rarely requires supplementation in the typical American diet.
Vitamin C may have the most notoriety of the commonly available vitamin supplements due to Nobel Prize-winning biochemist Linus Pauling's controversial assertions that large doses of vitamin C can prevent the common cold, a position that a) showed that even Nobel Prize winners can be wrong, egregiously wrong (see also Brian Josephson and William Shockley) and b) proved to be not terribly accurate when studied, but very persistent in the journals of public opinion probably due to a lack of peer review in that forum.
In addition to its usual function of preventing scurvy, vitamin C is also used as a preservative for fresh fruit (especially apples, where it prevents enzymatic browning after the fruit is cut). In addition, food scientist and cookbook author Shirley Corriher, in her 1997 kitchen science book Foodwise, recommends adding vitamin C to some bread recipes to enhance gluten development.
Vitamin D is especially important for bones. There is evidence that people who live in cooler, cloudier climates, where sun exposure is less, benefit from some supplementation.
According to the first edition of Harold McGee's seminal kitchen science book On Food and Cooking, Vitamin E deficiencies are not especially common in the Western diet. However, supplements are sold and sometimes used as skin care lotions. Vitamin E is also sometimes used as a preservative for whole grain products.
Vitamin K (from the German Koagulationsvitamin) is used in the human body's blood clotting system and is not widely available as a supplement. It is contra-indicated for those on anti-coagulant therapy (Warfarin) and is useful in the treatment of ingestion of rat poison (Warfarin).
A number of substances are sold claiming to be vitamins but are not. See pseudovitamin for a list. These are often named using the "vitamin" naming convention, as in "Vitamin B17" (which is actually laetrile). A number of other substances were also once thought to be vitamins but later reclassified out of the vitamin category; occasionally one will run across these still being referred to using their old (generally pre-World War II) vitamin name, such as "Vitamin F" and "Vitamin B4". "Vitamin F" was the old name for essential fatty acids, which are essential for human nutrition but do not meet the definition of a vitamin any more than water does. "Vitamin B4" is adenine, which is no longer considered a vitamin as it is not necessary for human nutrition, although it is synthesized in the body and binds with other B complex vitamins. Taking any of these supplements is a waste of money, and in the case of "B17"/laetrile, can be hazardous to your health.
- ↑ http://www.bulkmsm.com/convention/C/p7.htm
- ↑ http://www.usatoday.com/news/health/2006-05-17-multivitamins_x.htm
- ↑ Gilbert S. Omenn, Gary E. Goodman, Mark D. Thornquist, John Balmes, Mark R. Cullen, Andrew Glass, James P. Keogh, Frank L. Meyskens, Jr., Barbara Valanis, James H. Williams, Jr., Scott Barnhart, Martin G. Cherniack, Carl Andrew Brodkin, Samuel Hammar. Risk Factors for Lung Cancer and for Intervention Effects in CARET, the Beta-Carotene and Retinol Efficacy Trial. JNCI Journal of the National Cancer Institute 1996 88(21):1550-1559.
- ↑ Ulrike Peters, Michael F. Leitzmann, Nilanjan Chatterjee, Yinghui Wang, Demetrius Albanes, Edward P. Gelmann, Marlin D. Friesen, Elio Riboli, and Richard B. Hayes. Serum Lycopene, Other Carotenoids, and Prostate Cancer Risk: a Nested Case-Control Study in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. Cancer Epidemiol Biomarkers Prev 2007 16: 962-968 doi: 10.1158/1055-9965.EPI-06-0861
- ↑ http://www.cdc.gov/mmwr/preview/mmwrhtml/00039032.htm
- ↑ Welch GN, Loscalzo J. Homocysteine and atherothrombosis. N Engl J Med 1998;338:1042-1050.
- ↑ Selhub J, Jacques PF, Wilson PWF, Rush D, Rosenberg IH. Vitamin status and intake as primary determinants of homocysteinemia in an elderly population. JAMA 1993;270:2693-2698
- ↑ Balk EM. Raman G. Tatsioni A. Chung M. Lau J. Rosenberg IH. Vitamin B6, B12, and folic acid supplementation and cognitive function: a systematic review of randomized trials. Archives of Internal Medicine. 167(1):21-30, 2007 Jan 8.
- ↑ What Vitamins Should I Be Taking, Doctor? Willett WC, Stampfer MJ. N Engl J Med 345:1819, December 20, 2001.
- ↑ Thomas MK, Lloyd-Jones DM, Thadhani RI, et al. Hypovitaminosis D in medical inpatients. N Engl J Med 1998;338:777-783.