Welcome to Impact Factor, your weekly dose of commentary on a new medical study. I’m Dr F. Perry Wilson.
Thirty billion dollars. That’s how much Americans spend every year on vitamins and supplements. And according to the most comprehensive analysis of their effects, most of that money is being wasted.
The “umbrella review,” appearing in the Annals of Internal Medicine, is a comprehensive reporting of randomized trials of vitamins and supplements that examined their effects on cardiovascular disease and overall mortality.
Including only randomized trials was a great choice. Observational studies of vitamin and supplement usage are plagued by what’s known as “healthy user bias”: Individuals who choose to take vitamins often engage in other healthful behaviors. Time and again, vitamins that looked promising in observational studies failed in large randomized trials. I’m looking at you, vitamin D.
Now we have all of the best data surrounding vitamins and supplements in one place, which allows me to say the following: There is no high-quality evidence that any vitamin or supplement has a beneficial effect on overall mortality.
But okay, I’ll give you the details.
The analysis included studies of 24 different interventions—I’ve listed most of them here—comprising 277 randomized trials and nearly a million patients. And, basically, bupkis.
The only intervention that had even moderate-quality evidence for protection against all-cause mortality was reducing salt intake, which, frankly, doesn’t sound like a vitamin or supplement to me.
To give fair play to the other findings, there was low-quality evidence that omega-3 fatty acids might protect against myocardial infarction and heart disease, and that folic acid might protect against stroke. There was moderate-quality evidence that a combination of calcium and our old friend vitamin D increased the risk for stroke.
But all of these effects were pretty small.
Why? Well, let’s remember that vitamins were, by and large, identified via their deficiency syndromes. We know that vitamin C is vital for life because without it, people get scurvy. But there has never been much rationale as to why a super-intake of any of these chemicals would give super-benefits to health.
To be fair, this is only looking at mortality and cardiovascular outcomes. It remains possible that vitamins and supplements might improve subjective quality of life. But you know what else improves quality of life? Money. And based on this study, you might want to save yours when you’re walking down the vitamin aisle.