Most vitamins, supplements do little to protect heart health

Multivitamins and the bulk of nutritional supplements do little to protect heart health, in some cases increasing a person’s risk for CV events, an analysis published in the Annals of Internal Medicine has found.

Though national guidelines don’t recommend the routine use of any dietary supplements, including antioxidants, iron and vitamins, the National Health and Nutrition Examination Survey found that between 1999 and 2012, more than half of Americans were taking at least one supplement per day. An additional 10% reported using at least four dietary supplements, and 2011 to 2014 NHANES data found 41% of supplement-takers were doing so to improve their overall health. 

“In 2013, the U.S. Preventive Services Task Force conducted a systematic review of the utility of vitamin and mineral supplements for CVD prevention and found little evidence to support use,” first author Safi U. Khan, MD, of West Virginia University, and co-authors wrote in the Annals of IM. “More recently, Jenkins and colleagues published a meta-analysis of randomized controlled trials (RCTs) of dietary supplements published through October 2017. They found some stroke benefit conferred by folate; no CVD benefit for multivitamins, vitamin C, vitamin D or calcium; and evidence for mortality harm for niacin and antioxidants.”

To clarify the role of dietary supplements in preventing CVD, Khan and his colleagues combed PubMed, CINAHL, the Cochrane Library, and journal websites to identify RCTs and meta-analyses of RCTs that considered the efficacy of nutritional supplements and dietary interventions on heart health. They eventually pulled nine systematic reviews and four new RCTs encompassing 227 total trials, 24 interventions and 999,129 participants.

Khan et al. generated 105 meta-analyses from the research, which explored the impact of supplements and interventions like reduced fat intake on CV outcomes like death, MI, stroke and coronary heart disease. 

The authors found moderate-certainty evidence that reduced salt intake decreased the risk for all-cause mortality in normotensive patients with a risk ratio (RR) of 0.90—a benefit that can likely be attributed to reduced blood pressure in those participants. The team also found moderate-certainty evidence that reduced salt intake reduced the risk for CV mortality in hypertensive patients.

Further low-certainty evidence suggested omega-3 long-chain polyunsaturated fatty acid (LC-PUFA) was associated with a lower risk of MI (RR 0.92) and coronary heart disease (RR 0.93). Folic acid was linked to a decreased risk of stroke (RR 0.80), while a combo of calcium plus vitamin D seemed to increase a person’s risk of stroke (RR 1.17).

Other nutritional supplements studied—vitamin B6, vitamin D, multivitamins, antioxidants, iron and dietary interventions like restricted fat intake—had no significant effect on mortality or CVD outcomes.

Khan and colleagues said their findings need to be considered in the context of certain limitations, including the fact that their broad study wasn’t designed to stratify results by age, sex, BMI, lipid values, blood pressure thresholds or prior history of CVD. There are also inherent limitations to RCTs and meta-analyses that might have affected results.

“Overall, these findings are limited by suboptimal quality of the evidence,” the authors wrote. “This study can help those who create professional cardiovascular and dietary guidelines modify their recommendations, provide the evidence base for clinicians to discuss dietary supplements with their patients and guide new studies to fulfill the evidence gap.”