It's Official. Vitamins Don't Do Much for Health - Medscape

For there to be a $30 billion market, there must be some pretty convincing evidence that vitamin supplements work to improve health, right.

Because the observational data are clear and compelling.

People with vitamin deficiencies are at higher risk for these bad outcomes.

Even people with lower levels of certain vitamins, not in the deficiency range, are at higher risk for cancer and cardiovascular disease.

It stands to reason that if lower levels are associated with bad outcomes, and supplements prevent you from having lower vitamin levels, then supplements could improve those outcomes.

Caveat: These were general-population studies, not studies of people with known vitamin deficiencies.

No analyses of individual vitamins — beta-carotene, vitamin A, vitamin E, vitamin D (with a whopping 32 randomized trials), and calcium supplements — showed significant benefit in terms of either cardiovascular disease or cancer.

So, what makes the act of taking a vitamin so compelling.

The authors also analyzed the adverse events in all these vitamin trials, though to assess harms they also included observational studies.

This may seem unfair — assessing benefit only with randomized trials but harms via randomized trials and observational studies.

But I think it's actually okay, given that the direction of bias in observational studies tends to favor vitamins given the "healthy-user effect." This is the idea that people who choose to take vitamins tend to make other healthy lifestyle choices, so if you see a harm from taking a vitamin in the observational setting, you probably want to pay attention to it.

Notable findings for the harm analysis included evidence that vitamin A use might increase the risk for hip fracture, that vitamin E use might increase the risk for hemorrhagic stroke, and that vitamin C or calcium use might increase the risk for kidney stones.

Why are the observational data that show lower vitamin levels linked to worse outcomes so powerful, and the randomized trial data of supplementation so weak.

Basically, healthier people have higher vitamin levels, and healthier people have less cardiovascular disease and cancer.

Vitamin levels are a marker of overall health, not a driver of overall health.

But to be fair, there probably isn't too much harm in taking that daily vitamin.

Taking a vitamin, though it is a small act, is nevertheless an act of self-care — a moment that we take for ourselves and ourselves alone — a commitment to try to be healthy.