No Scientific Proof That Multivitamins Promote Heart Health
Taking multivitamin/mineral (MVM) supplements does not prevent myocardial infarction, stroke, or death from a cardiovascular cause, according to a comprehensive meta-analytic review of relevant research.
"The take-home message is simple: there is no scientific evidence that MVM supplements promote cardiovascular health. We hope that our paper helps to settle the controversy on MVM use for CVD prevention," lead author Joonseok Kim, MD, University of Alabama at Birmingham, told theheart.org | Medscape Cardiology.
The study was published online today in Circulation: Cardiovascular Quality and Outcomes.
"Vitamin and mineral supplements are taken by nearly half of US adults, yet few benefits have been documented," said JoAnn Manson, MD, who was not involved in the study and is chief of preventive medicine, Brigham and Women's Hospital and professor of medicine, Harvard Medical School, both in Boston, Massachusetts.
Multivitamin supplements will never be a substitute for a healthful and balanced diet. Dr JoAnn Manson
"Regarding multivitamins and cardiovascular disease, specifically, neither observational studies nor randomized clinical trials have demonstrated clear benefits for primary or secondary prevention," Manson told theheart.org | Medscape Cardiology.
"Importantly, clinicians should emphasize with their patients that multivitamin supplements will never be a substitute for a healthful and balanced diet, which have many beneficial components for vascular health. Additionally, micronutrients in food are typically better absorbed by the body than those from supplements," she advised.
Kim and colleagues did a systematic review and meta-analysis of 18 studies with more than 2 million adults (mean age, 57.8 years) with mean follow-up of 11.6 years. Eleven studies were from the United States, 4 from Europe, and 3 from Japan. Only 5 studies specified the dose and type of MVM supplement.
Overall, there was no association between MVM supplement use and cardiovascular disease (CVD) mortality, the investigators report.
Table. MVM Supplementation and Outcome Risks
Outcome Relative Risk (95% Confidence Interval) CVD mortality 1.00 (0.97 - 1.04) Coronary heart disease mortality 1.02 (0.92 - 1.13) Stroke mortality 0.95 (0.82 - 1.09) Stroke incidence 0.98 (0.91 - 1.05)
There was also no link between MVM supplements and CVD or coronary heart disease (CHD) mortality in prespecified subgroups categorized by mean follow-up; mean age; period of MVM use; sex; type of population; exclusion of patients with history of CHD; and adjustment for diet, adjustment for smoking, adjustment for physical activity, and study site.
MVM supplement use did appear to be associated with a lower risk for CHD incidence (relative risk [RR], 0.88; 95% confidence interval [CI], 0.79 - 0.97). However, this association did not remain significant in the pooled subgroup analysis of randomized controlled trials (RR, 0.97; 95% CI, 0.80 - 1.19).
"It has been exceptionally difficult to convince people, including nutritional researchers, to acknowledge that multivitamin and mineral supplements don't prevent cardiovascular diseases," Kim said in a news release. "I hope our study findings help decrease the hype around multivitamin and mineral supplements and encourage people to use proven methods to reduce their risk of cardiovascular diseases — such as eating more fruits and vegetables, exercising and avoiding tobacco."
The American Heart Association does not recommend use of MVM supplements for CVD prevention.
"Plausible but Failed Practice"
In a linked editorial, Alyson Haslam, MD, and Vinay Prasad, MD, both from Oregon Health & Science University in Portland, note that practices in biomedicine are often adopted because they "appeal to our hopes and there is biologic plausibility.
In the case of multivitamins, it is logical that some vitamins may reduce cardiovascular events because they are anti-inflammatory or more broadly improve health and well-being. Yet, in this case, it appears they do not, and as such, multivitamins for cardiovascular disease joins the list of plausible but failed practices in cardiology," they conclude.
Although multivitamins tend to be moderately dosed and are likely to be safer than mega-doses of individual dietary supplements, "they are not completely free of risk in all patients," Manson told theheart.org | Medscape Cardiology.
For example, dietary supplements may interact with some medications, such as vitamin K and warfarin; interfere with the measurement of some clinical laboratory tests, such as biotin and troponin levels; they also have side effects, such as gastrointestinal symptoms, for some patients, she explained.
"Thus, routine multivitamin supplementation is not recommended for the general population, but a targeted approach is appropriate for certain life stages and high-risk groups," said Manson.
Some examples of relevant life stages include pregnancy, where supplementation with folic acid/prenatal vitamins is of benefit, and in midlife or older adults, some of whom may benefit from supplemental vitamin B12, vitamin D, and/or calcium. High-risk groups, such as those with malabsorption syndromes, restricted eating patterns, osteoporosis, pernicious anemia, and age-related macular degeneration, and those with long-term use of metformin or proton-pump inhibitors also may benefit from dietary supplements, she said.
Manson also noted that the Physicians' Health Study II, a large-scale randomized clinical trial of multivitamins in men, demonstrated that these supplements may modestly reduce the incidence of cancer. This finding is being explored further in the ongoing COSMOS trial, which is testing whether multivitamins, with or without cocoa flavonols, can reduce the risk for cancer and CVD in older men and women.
"Results from the COSMOS trial are expected in 2 years, so stay tuned," said Manson.
The authors report no outside funding or relevant disclosures. Prasad has received royalties from his book Ending Medical Reversal and payments for contributions to Medscape.