Nutritional supplements and dietary interventions enjoy widespread use in the United States, but most have no effect on cardiovascular survival or outcomes, according to a group of U.S. researchers.
More than half of American adults use at least one dietary supplement, according to a 2016 study published in JAMA, and that figure is even higher among older adults — a 2017 study in The Journal of Nutrition found that 70% of individuals ages 60 and older use at least one supplement, and nearly 1 in 3 use four or more supplements. These products are part of a multibillion-dollar industry that is subject to scant regulation.
“I am not sure patients — or even all healthcare providers — realize that manufacturers of dietary supplements do not need FDA approval before producing or selling dietary supplements,” says Erin Michos, MD, MHS, FACC, FAHA, Associate Professor of Medicine and Epidemiology and Associate Director of Preventive Cardiology at the Ciccarone Center for the Prevention of Heart Disease, Division of Cardiology, Johns Hopkins Medicine. “Notably, dietary supplements are not intended to treat, diagnose, cure or alleviate the effects of diseases. However, many patients specifically take them … to improve their health.”
Supplements are appropriate for certain individuals with diagnosed nutritional deficiencies, experts say, but a growing body of evidence advises against routine use for the purpose of improving cardiovascular or overall health. In a 2018 study, for example, David Jenkins, MD, PhD, DSc, Professor in the Departments of Nutritional Sciences and Medicine at the University of Toronto and St. Michael’s Hospital, and colleagues conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) of supplement effects on cardiovascular disease outcomes and all-cause mortality, and they found no consistent benefits for multivitamins, vitamin D, calcium and vitamin C supplements.
“I don’t think anyone’s come to the conclusion that supplements are the answer to good health,” Dr. Jenkins says. “I think that’s been the prevailing view for a very long time.”
A Dearth of Benefits
Dr. Michos was part of a team of researchers that conducted a systematic review of meta-analyses of RCTs published through March 2019 to assess the certainty of evidence regarding the efficacy of various supplements and dietary interventions for prevention of cardiovascular disease. In analysis that included 277 RCTs involving nearly 1 million participants, the team evaluated 16 common supplements and eight dietary interventions. The findings appear in Annals of Internal Medicine.
Most supplements and diets neither reduced nor increased risk of mortality or cardiovascular disease, but a small number conferred benefits. Omega-3 fatty acid (fish oil) supplements reduced heart attack risk by 8% and coronary artery disease risk by 7%. People with normal blood pressure who followed a low-salt diet saw a 10% reduction in mortality, and people with hypertension who adhered to the same diet reduced their risk of heart disease-related death by 33%. Individuals who used folic acid supplements reduced their stroke risk by 20%. Most of that data, however, came from China, where food is not fortified with folic acid as it is in the United States. That calls into question whether Americans would enjoy similar risk reduction from additional folic acid.
Lead author Safi Khan, MD, Assistant Professor of Medicine at West Virginia University, was slightly surprised by the lack of heart-health benefits from the Mediterranean diet, given the positive effects demonstrated in other studies. Dr. Khan cautions, however, that trials of the Mediterranean diet are few, and Dr. Michos points out that it is notoriously difficult to study dietary interventions in randomized trials.
“I really believe that if we [were to] have more data on the Mediterranean diet … there is a possibility that it might show some effect, but at this point in time, the totality of evidence suggests the Mediterranean diet is not effective,” Dr. Khan says.
Emphasize Proven Interventions, Experts Say
Amitabh Pandey, MD, staff cardiologist in the Division of Cardiology at Scripps Clinic and Clinical Scholar at the Scripps Research Translational Institute in La Jolla, California, says the study adds to evidence that supplements, on the whole, do not live up to consumer hopes.
“More often than not, studies investigating supplements fail to show benefits, such that we once again are shown that there is no strong evidence for supplements in cardiovascular outcomes,” says Dr. Pandey, who was not involved in the research. “The authors of this study do a good job in showing the level of evidence for supplements, with most being uncertain or, at best, low certainty. We need to do better for our patients.”
For Dr. Khan, that means testing patients for nutritional deficiencies if suspicions exist and prescribing supplementation or replacement as appropriate, such as vitamin B12 for individuals with pernicious anemia. Dr. Khan and colleagues would like to perform subgroup analyses of the RCTs in the study and determine the degree of heterogeneity of the effects observed in RCTs versus observational studies, but the difficulty of obtaining individual-level data makes those tasks difficult, and they are not actively pursuing those lines of inquiry. Drs. Khan and Michos encourage physicians to have a frank discussion with patients about nutritional supplements and dietary interventions, and to continue to recommend the pillars of heart disease prevention: physical activity, a healthy diet, smoking cessation, stress management and compliance with treatment.