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

It’s Official. Vitamins Don’t Do Much for Health

This transcript has been edited for clarity.

welcome to impact factor, your weekly dose of commentary on a new medical study. I’m Dr. F. Perry Wilson from the Yale School of Medicine.

vitamins If you’re like most American adults, you’ve recently taken a vitamin or supplement. Over-the-counter sales of these products in this country total more than $30 billion a year. That’s more than the market for statins, and vitamins aren’t covered by insurance.

For there to be a $30 billion market, there has to be some pretty compelling evidence that vitamin supplements work to improve health, right?

Well, in the most comprehensive meta-analysis to date, Kaiser-Permanente researchers looked at numbers from virtually all randomized trials of vitamin supplements in adults to conclude that they basically do nothing.

Or, as we say in nephrology: vitamins make you pee expensive.

As many of you know, the US Preventive Services Task Force (USPSTF) makes evidence-based recommendations to Americans on a wide variety of health behaviors, from aspirin to prevention primary until detection of lung cancer.

The USPSTF commissioned researchers to update data on vitamin supplements with two important outcomes in mind: cancer and cardiovascular death. Why vitamins? Because the observational data is clear and convincing. People with vitamin deficiencies are at higher risk for these poor outcomes.

Even people with lower levels of certain vitamins, who are not in the deficiency range, are at increased risk of cancer and cardiovascular disease. It stands to reason that if lower levels are associated with poor outcomes, and supplements keep you from having lower vitamin levels, then supplements might improve those outcomes.

The researchers identified 87 randomized controlled trials of adults that evaluated at least one vitamin or multivitamin. Warning: These were general population studies, not studies of people with known vitamin deficiencies. The results do not necessarily need to be generalized to those with known deficiencies or disease states that promote deficiency.

There are a lot of vitamins, so there’s a lot to cover, but I’ll mention a few of the highlights.

Of all the multiple potential links between vitamins and outcomes, only one — the link between multivitamin use and cancer — showed any sign of benefit.


That’s a bit frustrating since “multivitamin” can mean a lot of things. There were nine randomized trials evaluating “multivitamins” that, when combined, show this effect, but the specific types of multivitamins ranged from a personalized antioxidant cocktail to Centrum Silver. So no, I don’t know which multivitamin you should take.

To be honest, the effect isn’t even that impressive: a 7% relative reduction in cancer incidence. And the relative risks really do tend to exaggerate the effect size. In absolute terms, multivitamins reduced the incidence of cancer by about 0.2%. That means you would need to treat 500 people with a multivitamin to prevent one case of cancer.

And while these studies did not specifically enroll patients with vitamin deficiencies, some of those enrolled may have. What we might be seeing is a small population effect based on the cumulative benefit for a small number of people who were actually vitamin deficient.

And that’s really the best finding of the entire study if you’re a vitamin lover.

No analysis of individual vitamins (beta-carotene, vitamin A, vitamin E, vitamin D (with 32 randomized trials), and calcium supplements) showed a significant benefit in terms of cardiovascular disease or cancer. They just don’t seem to do much.

So what makes the act of taking a vitamin so appealing? Why do so many of us, even knowing the data doesn’t really back it up, still take a pill every day? I think there are a couple of reasons.

First, we need to acknowledge the fact that vitamins are generally quite cheap and have a very low rate of side effects. They do not cause dizziness, nausea, tachycardia or fatigue. They don’t want anything.

Given the low risk, something like a Pascal bet plays out here. Sure, vitamins may not help, but they don’t seem to hurt, so why not take them, just in case?

Well, the truth is, they might actually hurt a bit. The authors also looked at adverse events in all of these vitamin trials, although to assess harm what’s more included observational studies. This may seem unfair: evaluating benefit only with randomized trials but harms through randomized trials and observational studies. But I think that’s actually fine, since 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 harm from taking a vitamin in the observation setting, you probably want to pay attention to it.

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

Why is the observational data showing lower vitamin levels linked to worse outcomes so powerful and the data from randomized trials of supplementation so weak? This is the classic confusion. Basically, healthier people have higher levels of vitamins, 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 much harm in taking that vitamin every day. We must not rule out here the ineffable value of ritual. Taking a vitamin, although it is a small act, is nonetheless an act of self-care, a moment we take for ourselves and ourselves alone, a commitment to try to be healthy. A brief moment of positivity in the morning may not reduce heart attacks or cancer rates, but it can still have benefits.

F. Perry Wilson, MD, MSCE, is an associate professor of medicine and director of the Yale Clinical and Translational Research Accelerator. His science communication work can be found in the Huffington Post, on NPR, and here on Medscape. he tweets @fperrywilson and hosts a repository of his communication work at www.methodsman.com.

Follow Medscape on Facebook, TwitterInstagram and YouTube

Leave a Comment

Your email address will not be published.