Megavitamins: Hype or Hope?
Supplement advertisers sound like Mae West: "Too much of a good thing is a good thing." Dr. Irwin Rosenberg, editor of the Tufts Health and Nutrition Newsletter, writes, "The vitamin marketplace has been something of a Wild West show, often placing marketing over science."
In the 1970s, vitamin C emerged as the first megavitamin, thanks to the work of American chemist Linus Pauling. His bestselling book, Vitamin C and the Common Cold, recommended megadoses of the supplement, although research has since debunked his theory.
Next into the spotlight vitamin E, thought to cure maladies ranging from heart disease to impotence. Clinical trials using high doses of the vitamin found no positive effect, and instead discovered potential harm (below).
Today's celebrity is vitamin D. And Dr.Rosenberg predicts:
If I had to guess the next vitamin of increasing attention, it will be vitamin B12. It may contribute to cognitive function during development and aging, and it may lack the adverse effects found at high doses.Recent Studies
Vitamin A/beta-carotene: Initial observations linked high doses of dietary beta-carotene (a precursor to vitamin A) with a reduced risk of lung cancer. Then large clinical trials found no benefit in lung cancer prevention, and increased risk to smokers.
B vitamins and folic acid: Some adults with Alzheimer's have low levels of vitamin B12. Supplements have been given to people with and without cognitive decline, but with disappointing results. In 2010, the Cochrane Collaboration, an international consortium of scientists, summed up the existing evidence: "Supplementation with vitamin B12 does not prevent or slow progression of the disease among those who already have Alzheimer's."
Epidemiology in the 1980s indicated that the B vitamins -- like folic acid -- could lower homocysteine, an amino acid that when elevated is thought to increase heart disease risk. But clinical trials using folate supplements showed no effect on heart disease, cancer, or mortality. Those clinical trials were conducted with people who already had disease, leading some scientists to conclude that the matter of B vitamin supplements and heart disease is still unresolved.
Vitamin D: Vitamin D is essential to many cellular functions, and its deficiency has been connected with many chronic illnesses. Today, vitamin D supplements are touted for preventing chronic illnesses. Many scientists wonder if this supplement will go the way of Vitamin E -- initial optimism subsequently unsubstantiated by large clinical trials.
A new study suggests a "Goldilocks effect" -- too much or too little vitamin D might be bad for your heart. Researchers found that increasing blood levels of vitamin D are associated with decreasing levels of C-reactive protein (CRP), a marker of inflammation linked to artery stiffness and potential heart problems. So that's good. But any increase in vitamin D beyond what's considered the low range of normal -- 21 nanograms per milliliter (ng/mL) -- was associated with CRP going up again. Each 100 IU of supplemental vitamin D raises blood levels by about 1 ng/mL.
For those at risk of osteoporosis who cannot get enough vitamin D from sun exposure and food, there is encouraging evidence that supplements can increase bone mineral density and decrease fractures. But precise supplement advice is blurry. It also appears that optimal bone health requires both vitamin D and calcium.
Consuming adequate amounts of vitamin D and calcium may reduce the risk of melanoma, at least among high-risk women. A recent study found that women with a history of basal cell or squamous cell carcinoma (the least dangerous types of skin cancer) were 57% less likely to develop melanoma (the most dangerous form) when they 1,000mg of calcium and 400 IU of vitamin D once a day for seven years. Many observational studies have linked vitamin D to a reduced risk of a variety of cancers, but this was one of the few clinical trials to demonstrate the benefit. The number of melanoma cases was very small, so more research is needed.
Vitamin E: Large daily doses of vitamin E have long been touted as a virtual wonder drug for protecting against heart disease, dementia and other ailments. But following the now-familiar pattern, large clinical trials using high dose supplements showed no benefit. One study even noted vitamin E doses above 400 IU per day (17 times the recommended doses) actually increased the risk of death. According to a recently released large federal study, it actually increased prostate cancer risk among middle-aged men by 17%.
The Bottom Line on Vitamin Supplements
Research in vitamin supplements is an extremely complicated process. The research doesn't attract the funding that the pharmaceutical companies are willing to commit to medications that have a greater potential for return on investment. So our knowledge of nutrition and vitamins remains insufficient, particularly with respect to their interconnection with chronic disease.
But here's the verdict, based on recent studies, on some of the popular vitamin supplements:
- Vitamin E for heart disease -- increased risk of mortality particularly for middle-aged men at risk for prostate cancer.
- Vitamin A/beta-carotene and lung cancer --increased risk in smokers.
- B vitamins and Alzheimer's
- Folic acid and heart disease
- Vitamin D and heart disease, cancer, diabetes
- Vitamin D (plus calcium) and osteoporosis
- Antioxide vitamins and age-related macular degeneration