Dietary supplements and multivitamins come in a variety of shapes and sizes, each claiming different effects, from anti-aging to improving heart health. But as diverse as these pills are, a review published Monday in The Annals of Internal Medicine suggests their effects can be homogenous — and not in a useful way. When it comes to heart health, the authors argue, many supplements you might find in a store are best left on the shelf.
"The evidence favoring use of vitamins, supplements is predominantly based on real world data, which are limited by various biases."
The study, led by scientists at the University of West Virginia, is a meta-analysis of 277 randomized controlled trials (involving a total of 992,129 people) investigating the effects of supplements, multivitamins, and diets on heart health. The end result, which reveals no significant impacts on heart health or all-cause mortality, serves the field a reality check.
“The evidence favoring use of vitamins, supplements is predominantly based on real world data, which are limited by various biases,” corresponding author Safi Khan, Ph.D., an assistant professor at the University of West Virginia’s School of Medicine, tells Inverse.
In particular, the team found that the following common vitamins, supplements, and diets had no significant impacts on heart health or all-cause mortality.
- Vitamin A
- Vitamin B6
- Vitamin C
- Vitamin E
- Vitamin D (by itself)
- Calcium (by itself)
- Iron supplements
- Mediterranean diet
- Diets low in saturated fats
Previous research pointed to the potential benefits that certain vitamins and diets conferred on heart health, but the new work suggests otherwise.
“Our study provides an evidence map derived from randomized controlled trials, the gold standard method for scientific evidence, for the patients and physicians regarding the effects of these products and allow them to understand that use of such products do not improve their cardiovascular health,” says Khan.
The vast majority of the supplements showed no effects, but there were some exceptions. Some were good, some were bad, and there were a few major caveats to consider.
The Positive Effects of Diets and Supplements
As far as diets go, a reduced-salt diet showed the most robust effects on heart health. In individuals who already had high blood pressure, a reduced-salt diet was associated with a decrease in risk of death from heart disease. And in people with normal blood pressure, lower salt was linked to a decrease in the risk of death from all causes.
Supplements had some small positive effects. Folic acid was associated with a 20 percent decrease in risk of stroke. There were also some minor but positive effects of omega-3 long-chain polyunsaturated fatty acids — one of two types of fatty acids (the other is omega-6). Omega-3s are usually found in fish oil supplements or flax seeds.
Omega-3s, they note, are associated with a slight decrease in the risk of coronary heart disease (about seven percent), but there are some reasons not to celebrate too soon.
Since the meta-analysis is a reanalysis of past studies, it can’t improve upon how precisely the data was collected the first time around. In particular, imprecision in the omega-3 research means that Khan takes it with a grain of salt:
“For instance, very low evidence suggested benefits of omega-3 fatty acids. That shows that there is still room for more robust evidence to establish their benefits,” he explains.
The Downside of Calcium Supplements
One of the study’s more devastating blows to supplements stems from its investigation of the combined effects of calcium and vitamin D supplements. The team reports that this combination is associated with a 17 percent increase in stroke risk.
This finding, however, raises more concerns about the calcium supplement side of the equation rather than the vitamin D side. The authors write that their results “raise concerns about harms from calcium supplement use.”
However, they also showed that vitamin D and calcium, taken individually, showed no effects on heart health, so there may be more to discover in this arena.
Vitamin D itself has a had a tumultuous year, thanks to a major review demonstrating that it had no additional effects on bone health in people who aren’t vitamin D deficient. (Boosting bone health is what vitamin D is famous for.)
Research on vitamin D’s other purported effects has also recently poured in, suggesting that it’s a hot topic of research. Some have focused on its effects on muscle function (in mice), on brain plasticity (in mice), and on the risk of schizophrenia in people who are deficient.
The Bigger Picture
Khan hopes his team’s paper can save consumers a bit of money when they’re strolling through the supplement aisle looking for an aide for heart health. “We hope that there will be debates on this topic, people will focus on healthy lifestyle and stop wasting their money on these products,” he says.
But that’s not to say that thinking about diet for heart health is a waste of time entirely. It’s just a reminder that for heart heart, supplements just aren’t a shortcut.
“People should focus on healthy diet from nutritional food sources, not vitamins or supplements, in combination with healthy lifestyle which included regular physical activity and not smoking,” he says.
Data Synthesis: Nine systematic reviews and 4 new RCTs were selected that encompassed a total of 277 trials, 24 interventions, and 992 129 participants. A total of 105 meta-analyses were generated. There was moderate-certainty evidence that reduced salt intake decreased the risk for all-cause mortality in normotensive participants (risk ratio [RR], 0.90 [95% CI, 0.85 to 0.95]) and cardiovascular mortality in hypertensive participants (RR, 0.67 [CI, 0.46 to 0.99]). Low-certainty evidence showed that omega-3 long-chain polyunsaturated fatty acid (LC-PUFA) was associated with reduced risk for myocardial infarction (RR, 0.92 [CI, 0.85 to 0.99]) and coronary heart disease (RR, 0.93 [CI, 0.89 to 0.98]). Folic acid was associated with lower risk for stroke (RR, 0.80 [CI, 0.67 to 0.96]; low certainty), whereas calcium plus vitamin D in- creased the risk for stroke (RR, 1.17 [CI, 1.05 to 1.30]; moderate certainty). Other nutritional supplements, such as vitamin B6, vitamin A, multivitamins, antioxidants, and iron and dietary interventions, such as reduced fat intake, had no significant effect on mortality or cardiovascular disease outcomes (very low– to moderate-certainty evidence).
Limitations: Suboptimal quality and certainty of evidence.
Conclusion: Reduced salt intake, omega-3 LC-PUFA use, and folate supplementation could reduce risk for some cardiovascular outcomes in adults. Combined calcium plus vitamin D might increase risk for stroke.