Here's a follow up to the Reuters report on America's vitamin obsession. Four researchers who participated in the National Institutes of Health conference answer questions about which vitamins they recommend and why. NPR's Allison Aubrey reports:
Dr. Meir J. Stampfer, Professor of Epidemiology and Nutrition, Harvard School of Public Health
How much is known about the health benefits of vitamins?
The list of vitamin supplements for which we have proven benefits is very short. But the list of supplements for which there are possible benefits is pretty long. You have to weigh the cost, risks and benefits while we're still waiting for clinical evidence.
Many people believe that natural supplements are always safe. Are there risks?
You can get too much of certain nutrients. For example, pre-formed vitamin A. It's not too hard to get to a level that's actually bad for you, which can increase the risk of fractures and birth defects. The vitamin companies have been responsive to this new data and have begun replacing pre-formed vitamin A with beta-carotene (which the body converts to vitamin A), which does not have the toxicity. We can't lose sight of the idea that just because it's natural doesn't mean it's necessarily safe. Tobacco and asbestos are natural, yet they are not safe.
Not so fast! In his book Eat to Live Dr. Fuhrman makes clear that isolated beta-carotene isn't the answer either:
Scientists are finding that taking beta-carotene supplements is not without risk, and supplements are certainly a poor substitute for the real thing—the assortment of various carotenoid compounds found in plants.
The reason researchers believed beta-carotene had such a powerful anti-cancer effect was that populations with high levels of beta-carotene in their bloodstream had exceedingly low rates of cancer. More recently we found out that these people were protected against cancer because of hundreds of carotenoids and phytochemicals in the fruits and vegetables they were consuming. It wasn't that beta-carotene was responsible for the low incidence of cancer; it merely served as a flag for those populations with a high fruit and vegetable intake. Unfortunately, many scientists confused the flag for the ship.
Recently, large scale studies have shown that beta-carotene (or vitamin A) in supplemental form may not be such a great idea.1
In Finnish trials, taking beta-carotene supplements failed to prevent lung cancer and actually increased its incidence.2 This study was halted when the researchers discovered that the death rate from lung cancer was 28 percent higher among participants who had taken the high amounts of beta-carotene and vitamin A. Furthermore, the death rate from heart disease was 17 percent higher for those that had taken the supplements than for those just given a placebo.3
Another recent study showed a similar correlation between beta-carotene supplementation and increased occurrence of prostate cancer. At this point, as a result of these European studies, as well as similar studies conducted here in the United States,4 articles in the Journal of the National Cancer Institute, the Lancet, and the New England Journal of Medicine all advise us to avoid taking beta-carotene supplements.5
We can learn a lesson from this research. A high intake of isolated beta-carotene may impair absorption of other carotenoids. Taking beta-carotene or vitamin A may hinder carotenoid anti-cancer acitivity from zeaxanthin, alpha-carotene, lycopene, lutein, and many other crucial plant-derived carotenoids. When my patients ask what multivitamin they should use, I tell them I prefer they take a high-quality multi that does not contain vitamin A or plain beta-carotene. The supplement should contain mixed plant-derived carotenoids, not isolated beta-carotene.
1. Mayne, S.T. 1996. Beta-carotene, carotenoids, and disease prevention in humans. FASEB 10 (7): 690-701.
2. Goodman, G.E. 1998. Prevention of lung cancer. Current Opinion in Oncology 10 (2): 122-26.
3. Kolata, G. 1996. Studies find beta carotene, taken by millions, can't forestall cancer or heart disease. New York Times, January 19.
4. Omenn, G.S., G.E. Goodman, M.D. Thornquist, et al. 1996. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N. Eng. J. Med. 334 (18): 1150-55; Hennekens, C.H., J. E. Buring, J.E. Manson, et al. 1996. Lack of effect on long-term supplementation with beta-carotene on the incidence of malignant neoplasms and cardiovascular disease. N. Eng. J. Med. 334 (18): 1145-49.
5. Albanes, D., O. P. Heinonen, P.R. Taylor, et al. 1996. Alpha-tocopherol and beta-carotene supplements and lung cancer incidence in the alphatocopherol, beta-carotene cancer prevention study: effects of base-line characteristics and study compliance. J. Nat. Cancer Inst. 88 (21): 1560-70; Rapola, J.M., J. Virtamo, S. Ripatti, et al. 1997. Randomized trail of alpha-tocopherol and beta-carotene supplements on incidence of major coronary events in men with previous myocardial infarction. Lancet 349 (9067): 1715-20.