Multivitamin and Mineral Supplements Don’t Stave Off Heart Disease or Stroke: Meta-analysis

People who take multivitamin and mineral (MVM) supplements derive no protection from stroke, a new meta-analysis confirms, and they are no less likely to die from heart disease or stroke compared with their peers who don’t take vitamins.

The analysis involved 18 studies with a total of more than 2 million participants and 18 million person-years of follow-up.

More than a decade ago, the US Preventive Services Task Force and the National Institutes of Health each came out with recommendations against routinely taking vitamins as a way to prevent chronic diseases. Still, there’s a “popular belief that MVM supplements may help maintain and promote health,” say lead author Joonseok Kim, MD (University of Alabama at Birmingham), and colleagues.

Vitamins are also big business. “As many as 30% of Americans use multivitamin and mineral supplements, with the global nutritional supplement industry expected to reach $278 billion by 2024,” according to a press release for the meta-analysis, which was published online earlier this week in Circulation: Cardiovascular Quality and Outcomes.

Kim told TCTMD via email that he wasn’t surprised to learn from the meta-analysis that multivitamins weren’t protective. “But the fact that researchers have conducted 18 large-scale studies, including two randomized controlled trials, to examine the same topic was remarkable,” he added.

The take-home message here is clear, Kim said. “Clinicians should emphasize with their patients that multivitamin supplements cannot fill the nutrition gap and should not replace a heart-healthy diet.”

Taking the supplements in moderation “rarely causes harm, but it is not completely safe either. For instance, some ingredients in the MVMs can interact with certain medications and cause side effects,” or GI symptoms, he explained. “More importantly, the problem with multivitamin use is that it can give people a false sense that MVM can replace a heart-healthy diet. It can distract the public from following measures that are proven to be beneficial for cardiovascular health, including eating fruits and vegetables, and smoking cessation.”

Clinicians should emphasize with their patients that multivitamin supplements cannot fill the nutrition gap and should not replace a heart-healthy diet. Joonseok Kim

The meta-analysis included studies published between January 1970 and August 2016, with a mean follow-up duration of 11.6 years. Eleven of the 18 were conducted in the United States, four in Europe, and three in Japan. Only two of the studies were randomized controlled trials that tested multivitamins with uniform doses and ingredients. The rest were prospective cohort studies, which ascertained intake through self-reporting.

Cardiovascular disease mortality and coronary heart disease mortality risks were similar regardless of whether individuals took multivitamins, as were the odds of stroke mortality and stroke incidence. For CVD and coronary heart disease (CHD) mortality, results were consistent across subgroups divided by follow-up period, age, timing of vitamin use, sex, type of population, and CHD history, as well as when numbers were adjusted for diet, smoking, physical activity, and study site.

The only endpoint to favor vitamin use was CHD incidence (RR 0.88; 95% CI 0.79-0.97). Here, the benefit was most acute in studies that did not adjust for vegetable and fruit intake. Moreover, this hint of an advantage to multivitamins disappeared when researchers restricted their analysis to pooled data from the randomized controlled trials.

Time to Move on From Multivitamins

In an accompanying editorial, Alyson Haslam, PhD, and Vinay Prasad, MD (Oregon Health & Science University, Portland), take a skeptical stance, noting that the result for CHD incidence was “driven primarily by observational studies.”

Observational studies, by nature, are vulnerable to confounding. This is especially true, they say, “in studies that evaluate dietary exposures, in part because dietary or supplement use is tied to broader patterns of socioeconomics and lifestyle.”

The difference in CHD incidence based on whether studies adjusted for fruits and vegetables is a hint that confounding may be at work, Haslam and Prasad say. “Fruits and vegetables can be more expensive than other foods when considering the cost per calorie, so people who consume more fruits and vegetables may be more likely have different overall diet habits, different access to healthcare, and different engagement in other salutatory health behaviors.”

Adjustment can remove some but not necessarily all confounding, they argue. Additionally, there’s the possibility that choosing exactly which variables to adjust for can also alter results.

All that said, the meta-analysis’ findings aren’t too surprising in today’s world, the editorialists conclude.

“Preventing or treating disease with vitamin supplements was relatively simple when foods were limited, frank vitamin deficiency was possible, and common diseases had a clear etiology, such as vitamin C deficiency for scurvy or thiamine deficiency for beriberi,” they explain. “Now that diets are more varied, supplemented, and fortified, diseases of frank vitamin deficiency are rare, and the most commonly occurring diseases have a multifactorial etiology. It may be unlikely for a supplement ingested once a day to confer a health benefit, and the study by Kim and colleagues provides no reason to take one.”

Kim agrees it’s time to move on.

“The scientific community has spent tremendous time and resources to investigate the association between MVM supplements and CVD risk, and our study demonstrated that there is no benefit of using MVM supplements for CVD prevention,” he said to TCTMD. “I believe healthcare professionals and researchers now have enough evidence to educate the public with correct information regarding MVM supplements and CVD health, and to focus on more pressing questions for effective CVD prevention.”