Nutritional supplements and dietary interventions offer little protection against heart disease, says research
When it comes to vitamins and mineral supplements, researchers have a piece of simple advice: do not waste your money on them. Few protect against heart attacks and strokes, and others might be harmful to your health, according to a large-scale review of evidence.
Researchers from West Virginia University analyzed 277 randomized controlled trials comprising nearly 1 million people to evaluate and determine whether 16 different nutritional supplements and eight dietary interventions offered any protection against cardiovascular diseases or death.
They found that only a few of the 16 nutritional supplements and one of the eight dietary modifications evaluated had some proven effects in cardiovascular risk reduction. The remaining nutritional supplements or dietary interventions reviewed did not play a role in preventing cardiovascular diseases.
According to the World Health Organization (WHO), cardiovascular diseases (CVDs) - a group of disorders of the heart and blood vessels - are the number one cause of death globally. An estimated 17.9 million people died from cardiovascular diseases in 2016, representing 31% of all global deaths. Of these deaths, 85% are due to heart attack and stroke.
“The reason we conducted the study was because nearly one million people in the US and across the world consume these supplements, but there was no good quality evidence to suggest whether these have any effect in cardiovascular protection or not. So we selected high-quality randomized controlled trials. We gathered the information from a maximum amount of intervention supplements and dietary. The most important thing was whether these supplements had any effect on improving the survival and heart cardiovascular outcome - something like myocardial infarction, stroke, and even coronary heart disease,” say the researchers in their study.
“Diets and supplements are two of the most intense areas of public interest but are among the most lacking in adequate data. The use of supplements continues to increase in the US and worldwide, largely without evidence for their efficacy or safety. Nearly 3 in 4 persons in the US use some form of supplements, so it is no wonder that the supplement market is estimated to reach nearly $300 billion in the next five years. In addition to the unbridled uptake, the US Food and Drug Administration lacks regulatory authority over supplements. Yet, the safety of supplements remains unclear, with several studies showing potential harm due to dosing or impurities. Similarly, there are limited data to support or refute the health claims of various diets,” according to an accompanying editorial from Scripps Research Translational Institute.
The researchers studied several supplements, including vitamin B6, fish oil, folate, vitamin A, multivitamins, antioxidants, and iron. In the study, fish oil supplementation was found to be protective against heart attack, while folic acid showed some protective benefit for stroke. “Omega-3, long-chain fatty acids were protective for myocardial infarction and coronary heart disease,” says the paper.
The researchers, however, say that while omega-3 fatty acid might be helpful, there are better cardiovascular medications which can provide people with more robust benefits compared to this.
Other supplements, such as multivitamins, selenium, vitamin A, vitamin B6, vitamin C, vitamin E, vitamin D alone, calcium alone, folic acid, and iron, did not offer any protection against cardiovascular diseases or death.
The researchers caution that some of the supplements studied are associated with substantial harms. According to the paper, evidence suggests that a combination of calcium and vitamin D was associated with a higher risk of stroke.
When it came to diets, there was less beneficial evidence. The team examined the Mediterranean diet, reduced dietary fat, modified dietary fat, and reduced saturated fat intake. They found that none of these dietary modifications had any effect on cardiovascular risk.
Only one dietary intervention, according to them, had notable benefits, but only for specific patients. The researchers found some evidence that a reduced sodium diet/salt intake was associated with improvement in survival in patients who did not have hypertension and reduction in cardiovascular deaths in patients who had hypertension.
"There is some evidence that reduced salt intake was protective for all-cause mortality in participants with normal blood pressure. But the beneficial effects of reduced salt intake on mortality and cardiovascular risk reduction remain a debatable issue. The mechanism behind the benefit of reduced salt intake on death is most likely related to reduced blood pressure. Hypertension is a known risk factor for cardiovascular disease, and scientific evidence exists of a direct relationship between dietary salt intake and blood pressure,” says the study.
Current US dietary guidelines recommend several healthy eating patterns, including US, Mediterranean, and vegetarian diets. Although the guidelines recognize the occasional need for nutritional supplementation or food fortification for specific nutrients that may be consumed in inadequate amounts, they do not recommend routine use of any dietary supplement toreduce the risk for cardiovascular disease or other chronic diseases. The researchers say that despite these recommendations, most US adults use supplements to enhance their diets, with uncertain health benefits.
“From 1999 to 2012, the NHANES (National Health and Nutrition Examination Survey) reported that 52% of participants used at least one, and 10% used at least four dietary supplements. From 2011 to 2014, the NHANES reported that among participants aged 60 years or older, 70% used at least one, 29% used at least four supplements, and 41% of supplement takers reported that they did so to improve their overall health,” says the paper.
Further, in 2013, the US Preventive Services Task Force conducted a systematic review of the utility of vitamin and mineral supplements for cardiovascular disease prevention and found little evidence to support use.
“The US Department of Health and Human Services and the US Department of Agriculture have been criticized for the lack of sound scientific background behind their dietary recommendations. Similarly, the US Preventive Services Task Force report has not been updated since 2014. Our review provides a direct quantitative comparison of various nutritional and dietary interventions for cardiovascular outcomes,” say the researchers in their findings, adding that more studies are needed in this area.
According to the accompanying editorial, the findings might be limited by the quality of the evidence. For example, geographic considerations among the studies need to be considered.
“The reported benefit of folate seems to be largely driven by the inclusion of one study from China, where a folate-rich diet is not routine. In addition, most studies rely on food diaries, which are based on a person’s memory of what they consumed and therefore, are not wholly reliable. However, for now, it is reasonable to hold off on using supplements or diet modification for the purpose of cardiovascular disease prevention in all guidelines and recommendations,” says the editorial.
The study has been published in the Annals of Internal Medicine.