Fast on the heels of recent studies questioning the benefits of vitamin D pills, three new studies in a prominent U.S. medical journal cast strong doubt on the use of nutritional supplements overall.
Most vitamin and mineral supplements are ineffective and some – including beta-carotene, vitamin E and high doses of vitamin A – may cause harm, according to an editorial published this week in the Annals of Internal Medicine. The evidence that supplements do not prevent chronic disease or death is so conclusive, according to the authors, that they urged the public to “stop wasting money on vitamin and mineral supplements.”
More than half of U.S. adults take some form of supplement, the authors noted. But in a general population with no clear evidence of micronutrient deficiency, taking supplements is either useless or risky.
Various studies over the years have debunked multivitamins, according to Dr. Reinhold Vieth, a professor in the department of nutritional sciences at the University of Toronto. The reason multivitamins are generally ineffective in disease prevention is that they provide no bonus once a person has met the recommended dietary allowance of micronutrients from food, Vieth explained. “Beyond a certain point, you have no further benefit,” he said.
Multivitamins do not play a role in disease prevention, according to three studies recently published in the Annals of Internal Medicine. Data from a large randomized controlled trial showed that long-term use of a daily multivitamin does nothing to slow cognitive decline in older men. Researchers assigned nearly 6,000 male physicians aged 65 and older to take either a multivitamin or placebo for 12 years. The men’s cognitive functions were tested at the outset and at three intervals throughout the study. A dozen years later, the researchers found no difference in cognitive decline between the multivitamin users and the placebo group.
A separate study looked at whether vitamin and mineral supplements protected against a second cardiovascular event in patients in stable condition after a heart attack. Researchers assigned 1,700 heart attack patients aged 50 years or older to take a high-dose multivitamin pill, multimineral supplement or placebo. After a median follow-up of 4.6 years, researchers found no increased or decreased risk of chest pain requiring hospitalization, heart attack, stroke or death among the different groups.
The conclusions are consistent with the findings of a systematic review published earlier this fall. Researchers analyzed 26 trials on supplements and found limited evidence to support any benefit from vitamin and mineral supplementation for the prevention of cancer or heart disease.
Multivitamins have been so thoroughly debunked that further research on their benefits in disease prevention would be a wasted effort, the editorialists wrote. The exception is vitamin D supplements, especially in deficient people, since some trials suggest that taking vitamin D may prevent falls in older people. Although further research is needed to clarify appropriate use of vitamin D supplementation, “current widespread use is not based on solid evidence that benefits outweigh harms,” the authors noted.
Vieth challenged recent reports that vitamin D supplements are ineffective, citing selection bias as a reason for misleading conclusions in widely publicized meta-analyses. A recent review published in the Lancet found that vitamin D did not improve bone density, but according to Vieth, bone density is unrelated to the rate of falls in older people. “For bone health, vitamin D is essential,” he said.
But Vieth agreed with the statement that further research on multivitamins is unnecessary. “It’s probably a dead horse,” he said.