Guidelines

Evidence still lacking that vitamins prevent CVD, cancer: USPSTF


 

FROM JAMA

There is not enough evidence to recommend for or against taking most vitamin and mineral supplements to prevent heart disease, stroke, and cancer, a new report by the U.S. Preventive Services Task Force concludes.

However, there are two vitamins – vitamin E and beta-carotene – that the task force recommends against for the prevention of heart disease, stroke, and cancer. Evidence shows that there is no benefit to taking vitamin E and that beta-carotene can increase the risk for lung cancer in people already at risk, such as smokers and those with occupational exposure to asbestos.

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These are the main findings of the USPSTF’s final recommendation statement on vitamin, mineral, and multivitamin supplementation to prevent cardiovascular disease and cancer. The statement was published in JAMA.

“This is essentially the same recommendation that the task force made in 2014,” USPSTF member John Wong, MD, professor of medicine at Tufts University, Boston, said in an interview.

“We recognize that over half of people in the U.S. take a vitamin supplement of some sort every day and 30% take a vitamin/mineral combination. We wanted to review the evidence again to see if there was any benefit in terms of reducing the risk of cardiovascular disease or cancer or increasing the chances of living longer,” Dr. Wong explained.

“We looked hard for evidence, reviewing 84 studies in total. But we did not find sufficient evidence in favor of taking or not taking vitamins, with the two exceptions of beta-carotene and vitamin E, which we recommend against taking,” he noted.

Although there is evidence of some harm with beta-carotene, the main reason behind the recommendation against taking vitamin E is the consistent evidence of no benefit, Dr. Wong explained.

“While the evidence for some other vitamins is conflicting, there is more consistent evidence of no benefit for vitamin E,” he said.

The bulk of new evidence since the last review in 2014 was predominately for vitamin D supplementation, but despite the inclusion of 32 new randomized, controlled trials and two cohort studies, pooled estimates for all-cause mortality were similar to those in the previous review, with confidence intervals only slightly crossing 1, and point estimates that suggest at most a very small benefit, the task force noted.

“Apart from beta-carotene and vitamin E, after reviewing 84 studies – including 78 randomized controlled trials – in over a million patients, we can find no clear demonstration of benefit or harm of taking vitamins in terms of developing cardiovascular disease or cancer or the effect on all-cause mortality. So, we don’t know whether people should take vitamins or not, and we need more research,” Dr. Wong added.

On the use of a multivitamin supplement, Dr. Wong noted that the complete body of evidence did not find any benefit of taking a multivitamin on cardiovascular or cancer mortality. But there was a small reduction in cancer incidence.

However, he pointed out that the three studies that suggested a reduction in cancer incidence all had issues regarding generalizability.

“The recently published COSMOS trial had an average follow-up of only 3.6 years, which isn’t really long enough when thinking about the prevention of cancer, one of the other studies only used antioxidants, and the third study was conducted only in U.S. male physicians. So those limitations regarding generalizability limited our confidence in making recommendations about multivitamins,” Dr. Wong explained.

But he noted that the task force did not find any significant harms from taking multivitamins.

“There are possible harms from taking high doses of vitamin A and vitamin D, but generally the doses contained in a multivitamin tablet are lower than these. But if the goal for taking a multivitamin is to lower your risk of cancer or cardiovascular disease, we didn’t find sufficient evidence to be able to make a recommendation,” he said.

Asked what he would say to all the people currently taking multivitamins, Dr. Wong responded that he would advise them to have a conversation with a trusted health care professional about their particular circumstances.

“Our statement has quite a narrow focus. It is directed toward community-dwelling, nonpregnant adults. This recommendation does not apply to children, persons who are pregnant or may become pregnant, or persons who are chronically ill, are hospitalized, or have a known nutritional deficiency,” he commented.

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