Megavitamins: Too Much of a Good Thing?
Some antioxidants fail to prove their punch in key research
THURSDAY, Feb. 24, 2005 (HealthDay News) -- In the world of wellness, loading up on vitamins has been a constant source of controversy.
Mainstream medicine has given antioxidant megavitamins some major tryouts and, so far, the vitamins have failed in the key studies.
Antioxidant vitamin supplements took a real licking last year.
A Johns Hopkins University study of vitamin E suggested that a daily dose of 400 IUs (international units) or more was linked to a 6 percent increased risk of death. In the analysis of 136,000 patients, the risk of death starts to increase at 150 IU, but at 400 IU, the risk of dying from any cause rises about 10 percent.
"People take significant amounts of vitamin E because they have a perception that it will provide some health benefit, and that this will help them live longer. But just the opposite could be the case," said study author Dr. Edgar R. Miller, an associate professor of medicine. There is no recommended dose for vitamin E, although guidelines set a tolerable limit of up to 1,500 IUs per day. Daily intake of vitamin E through foods is 10 IUs, and multivitamin pills usually contain 30 to 60 IUs of vitamin E. So, 400 IUs is a lot.
But it was just another blow to the once-popular concept that extra doses of the antioxidant vitamins -- E, C and beta carotene (a plant pigment called a carotenoid that the body converts into vitamin A) -- would beef up the body's chemical reactions to dangerous free radicals, with health-promoting effects such as preventing lung cancer or heart disease for ex-smokers.
The Hopkins vitamin E study was a re-analysis of the data from 19 vitamin E studies over the past decade. The vitamin-supplement industry immediately attacked the study's methodology. And the study may not stop dedicated believers from taking high doses of vitamin E, much to the chagrin of physicians who have trouble getting patients to take agents with documented efficacy.
And beta carotene? Previously, high doses of beta carotene had been shown to increase the risk for lung cancer and death compared with the risk to those in the controlled trial who got a placebo.
Late in the year, beta carotene got more bad news, at least for women. Six years after a study was halted early because the risky effects of high-dose beta carotene to heart disease and cancer were detected, follow-ups showed that for women, the bad effects lingered. The participants took 30 milligrams a day, about 10 times the amount in a daily multivitamin supplement, combined with 25,000 IUs of retinyl palmitate, a drug also thought to be a cancer fighter.
The study organizers found the increased risk of heart disease and cancer disappeared when the men in the study, all former smokers or those with asbestos exposure, stopped taking the beta carotene supplements. But for women it didn't work. Before the study was halted, the participants who took the supplement had a 28 percent greater incidence of lung cancer and 17 percent more deaths from all causes compared with those who didn't take the beta carotene. In the follow-up, women were 30 percent more likely to develop lung cancer, 40 percent more likely to die of heart disease, and 30 percent more likely to die of all other causes.
This may be because beta carotene and vitamin E are both fat-soluble, allowing any excess to accumulate in fat-cell membranes. This could explain the adverse effects of beta carotene in women, who have more body fat than men. Vitamin C is water-soluble, and any excess leaves the body via urine.
High doses of vitamin C, while not fulfilling the claims of its advocates, have not been shown to be dangerous, although the noted hematologist and strident critic of fad diets, the late Dr. Victor Herbert of the Bronx Veterans Administration, attempted to link supplements of iron or vitamin C, or both, to iron-balance pathology.
To learn more about beta carotene, visit the National Library of Medicine.