Americans spend billions in dietary supplements every year but, in truth, this money is only wasted, according to evidence form a recent study published in Intern Med.
Most of dietary interventions and nutritional supplements including multi-vitamins, selenium and antioxidants, do not reduce cardiovascular risk or mortality, according to this large analysis and systematic revision of several randomized studies.
Modest benefits were indeed observed when reducing salt consumption and when incorporating omega 3 polyunsaturated fatty acids and folic acid.
On the other hand, combining calcium and vitamin D seems to increase stroke risk.
However, despite different guidelines and societies claim the evidence behind these recommendations is insufficient, one every other American consume some sort of vitamin or dietary supplement, and the proportion increases with age.
In this context, researchers wanted to provide quality evidence by testing the effect of nutritional supplements and, to this end, included 9 systematic reviews and 4 randomized studies with nearly one million participants. Data included studies VITAL and ASCEND, which studied the impact of vitamin D and omega-3.
Globally, they were able to find certain evidence that reduced salt consumption has a modest positive effect on global mortality in persons with normal blood pressure (RR 0.90; 95% CI 0.85-0.95) and a more significant positive effect on cardiovascular mortality in hypertensives (RR 0.67; 95% CI 0.46-0.99).
Additionally, “low certainty” evidence suggested omega-3 acids reduce the risk of infarction and heart disease.
There was also “low certainty” evidence that folic acid reduced stroke risk, though this benefit was driven basically by one single study conducted in China.
Finally, and with “moderate certainty”, calcium and vitamin D supplements would increase stroke risk (RR 1.17; 95% CI 1.05-1.30).
No other supplement, including vitamins A, B complex, C, D or E, antioxidants, iron or other dietary interventions (including reduced fat intake) impact mortality or cardiovascular events, neither positively nor negatively.
Most people are wasting their money in vitamins, buying supplements at the pharmacy, when it would be more sensible, rational and a lot cheaper to buy vitamins at the groceries’.
Most surprisingly, the “Mediterranean diet” showed no impact, seeing as the PREDIMED outcomes suggest the benefit of diets rich in vegetables, whole grains, nuts and olive oil. Researchers speculate these results might have been counterbalanced with other study results with null outcomes.
Original title: Effects of nutritional supplements and dietary interventions on cardiovascular outcomes: an umbrella review and evidence map.
Reference: Khan SU et al. Ann Intern Med. 2019;171:190-198.
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