Los Angeles—Even though more than half of adults in the U.S. use dietary supplements and vitamins—spending nearly $50 billion last year—an independent panel of national experts said there was "insufficient evidence" that taking multivitamins, paired supplements, or single supplements can help prevent cardiovascular disease (CVD) and cancer in otherwise healthy, nonpregnant adults.

The recommendations from the U.S. Preventive Services Task Force (USPSTF) were based on a systematic review of 84 studies, the USPSTF's new guidelines state.

"Patients ask all the time, 'What supplements should I be taking?' They're wasting money and focus thinking there has to be a magic set of pills that will keep them healthy when we should all be following the evidence-based practices of eating healthy and exercising," stated Jeffrey Linder, MD, MPH, chief of general internal medicine in the department of medicine at Northwestern University Feinberg School of Medicine in Chicago, Illinois.

Dr. Linder and colleagues from Northwestern Medicine wrote an editorial in the Journal of the American Medical Association (JAMA) in support of the new recommendations.

"The task force is not saying 'don't take multivitamins,' but there's this idea that if these were really good for you, we'd know by now," Dr. Linder stated.

The background information in the article about the new guidelines pointed out that CVD and cancer are the two leading causes of death in the U.S., and vitamin and mineral supplementation has been proposed to help prevent the conditions.

The benefits and harms of vitamin and mineral supplementation in healthy adults to prevent CVD and cancer were reviewed to inform the USPSTF. To do that, researchers used MEDLINE, PubMed (publisher-supplied records only), Cochrane Library, Embase (January 2013 to February 1, 2022), and prior reviews.

The study team focused on English-language randomized clinical trials (RCTs) of vitamin or mineral use among adults without CVD or cancer and with no known vitamin or mineral deficiencies, and observational cohort studies examining serious harms. Ultimately, 84 studies involving 739,803 participants were included in the pooled analyses.

The results indicated that multivitamin use was significantly associated with a lower incidence of any cancer (odds ratio [OR], 0.93 [95% CI, 0.87-0.99]; four RCTs [n = 48,859]; absolute risk difference [ARD] range among adequately powered trials, –0.2% to –1.2%) and lung cancer (OR, 0.75 [95% CI, 0.58-0.95]; two RCTs [n = 36,052]; ARD, 0.2%).

"However, the evidence for multivitamins had important limitations," the USPSTF cautioned, pointing out:

• Beta carotene (with or without vitamin A) was significantly associated with an increased risk of lung cancer (OR, 1.20 [95% CI, 1.01-1.42]; four RCTs [n = 94,830]; ARD range,-0.1%-0.6%) and cardiovascular mortality (OR, 1.10 [95% CI, 1.02-1.19]; five RCTs [n = 94,506] ARD range, -0.8%-0.8%).
• Vitamin D use was not significantly associated with all-cause mortality (OR, 0.96 [95% CI, 0.91-1.02]; 27 RCTs [n = 117,082]), CVD (e.g., composite CVD event outcome; OR, 1.00 [95% CI, 0.95-1.05]; seven RCTs [n = 74,925]), or cancer outcomes (e.g., any cancer incidence; OR, 0.98 [95% CI, 0.92-1.03]; 19 RCTs [n = 86,899]).
• Vitamin E was not significantly associated with all-cause mortality (OR, 1.02 [95% CI, 0.97-1.07]; nine RCTs [n = 107,772]), CVD events (OR, 0.96 [95% CI, 0.90-1.04]; four RCTs [n = 62,136]), or cancer incidence (OR, 1.02 [95% CI, 0.98-1.08]; five RCTs [n = 76,777]).

"Evidence for benefit of other supplements was equivocal, minimal, or absent. Limited evidence suggested some supplements may be associated with a higher risk of serious harms (hip fracture [vitamin A], hemorrhagic stroke [vitamin E], and kidney stones [vitamin C, calcium])," the researchers wrote.

The panel concluded that vitamin and mineral supplementation was associated with little or no benefit in preventing cancer, CVD, and death. An exception was the small benefit for cancer incidence with multivitamin use. On the other hand, they noted that beta carotene was associated with an increased risk of lung cancer and other harmful outcomes in people with a high risk of lung cancer.

The background information in the article explains that vitamin and mineral supplementation has been proposed as a preventive strategy for both diseases because of shared disease pathways that involve oxidative stress, inflammation, and methionine metabolism. In addition, "observational evidence has suggested associations between higher plasma levels of various vitamins and minerals and lower rates of cardiovascular disease and cancer," according to the USPSTF.

In 2014, the same panel recommended against the use of beta carotene or vitamin E to prevent CVD and cancer and concluded that the evidence was insufficient to assess the net benefit for multivitamins or the use of single- or paired-nutrient supplements.

"The harm is that talking with patients about supplements during the very limited time we get to see them, we're missing out on counseling about how to really reduce cardiovascular risks, like through exercise or smoking cessation," Dr. Linder stated.

Dr. Linder noted that individuals who have a vitamin deficiency can still benefit from taking dietary supplements, such as calcium and vitamin D, which have been shown to prevent fractures and possibly falls in older adults.

In addition, the new USPSTF guidelines do not apply to women who are pregnant or trying to get pregnant, according to JAMA editorial coauthor Natalie Cameron, MD, an instructor of general internal medicine at the Northwestern University Feinberg School of Medicine. "Pregnant individuals should keep in mind that these guidelines don't apply to them," she added. "Certain vitamins, such as folic acid, are essential for pregnant women to support healthy fetal development. The most common way to meet these needs is to take a prenatal vitamin. More data is needed to understand how specific vitamin supplementation may modify risk of adverse pregnancy outcomes and cardiovascular complications during pregnancy."

The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.