This transcript has been edited for clarity.
Welcome in Impact factor, your weekly dose comment for a new medical study. I’m Dr. F. Perry Wilson of Yale Medical School.
vitamins. If you’re like most older Americans, you’ve recently taken a vitamin or supplement. Over-the-counter sales of these products in this country amount to more than $ 30 billion a year. This is more than the statin market – and vitamins are not covered by insurance.
For there to be a $ 30 billion market, there needs to be some pretty convincing evidence that vitamin supplements work to improve health, right?
Well, in the most in-depth meta-analysis to date, researchers at Kaiser-Permanente analyzed the numbers from almost every randomized study of vitamin supplements in adults to conclude that they generally do nothing.
Or, as we say in nephrology: Vitamins give you expensive urination.
As many of you know, the US Special Preventive Services Group (USPSTF) makes evidence-based recommendations to the American people on a wide variety of health behaviors, from aspirin for primary prevention to lung cancer screening.
The USPSTF commissioned researchers to update data on vitamin supplements, keeping in mind two important results: cancer and cardiovascular death. Why vitamins? Because the data from the observations are clear and convincing. People with vitamin deficiencies are at higher risk of these poor outcomes.
Even people with lower levels of certain vitamins, which are not in the range of deficiency, are at higher risk of cancer and cardiovascular disease. Understandably, if lower levels are associated with poor results and supplements prevent you from having lower levels of vitamins, then supplements can improve those results.
The researchers identified 87 randomized controlled trials in adults evaluating 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 have to be summarized for those with known deficits or disease states that promote deficiency.
There are a lot of vitamins, so there is a lot to cover, but I will hit some of the highlights.
Of all the many potential links between vitamins and results, only one – the link between multivitamin use and cancer – shows some signal of benefit.
This is a bit disappointing, as “multivitamin” can mean many things. There have been nine randomized trials evaluating “multivitamins” that, when combined, show this effect, but specific types of multivitamins have varied, ranging from a personalized antioxidant cocktail to Centrum Silver. So no, I don’t know what multivitamins you should take.
Honestly, the effect is not even that impressive: 7% relative reduction in cancer incidence. And the relative risks do tend to overestimate the magnitude of the effect. In absolute terms, multivitamins reduce the incidence of cancer by about 0.2%. This means that you will need to treat 500 people with multivitamins to avoid one case of cancer.
And although these studies do not specifically include patients with vitamin deficiencies, some of those enrolled may have had them. What we can observe is the effect of a small population based on the benefits accumulated for a small number of people who have indeed been deficient in vitamins.
And this is really the best discovery in the whole study, if you are a lover of vitamins.
No analysis of individual vitamins – beta-carotene, vitamin A, vitamin E, vitamin D (with a huge 32 randomized trials) and calcium supplements – has shown significant benefits in terms of cardiovascular disease or cancer. They just don’t seem to do much.
So what makes vitamin intake so fascinating? Why do so many of us, even knowing that the data doesn’t really support it, keep taking the pill every day? I think there are several reasons.
First, we must recognize the fact that vitamins are generally quite cheap and have a very low rate of side effects. They do not make you dizzy or nauseous, have tachycardia or get tired. They don’t feel like much of anything.
Given the low risk, something like Pascal’s pledge is developing here. Of course, vitamins may not help, but they don’t seem to hurt, and why not take them – just in case.
Well, the truth is, they can actually hurt a little. The authors also analyzed adverse events in all of these vitamin studies, but to assess their harms. too includes observational research. This may seem unfair – assessing the benefits only with randomized trials, but the harm through randomized trials and observational studies. But I think it’s actually good, given that the direction of bias in observational studies tends to favor vitamins, given the “healthy consumer effect.” This is the idea that people who choose to take vitamins tend to choose another healthy lifestyle, so if you see the harm of taking a vitamin under observation, you probably want to pay attention to it.
Remarkable findings from the injury analysis include evidence that vitamin A use may increase the risk of femoral fracture, that vitamin E use may increase the risk of hemorrhagic stroke, and that vitamin C or calcium use may increase the risk of stones. in the kidneys.
Why are observational data showing lower levels of vitamins associated with poorer outcomes so powerful and data from randomized trials of supplements so weak? This is a classic confusion. In general, 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 an engine of overall health.
But to be honest, there’s probably not much harm in taking this daily vitamin. Here we should not reject the inexpressible value of the ritual. Taking a vitamin, even though it is a small action, is still an act of self-care – a moment we set aside for ourselves and only for ourselves – a commitment to try to be healthy. A brief moment of positivity in the morning may not reduce heart attacks or cancer, but it can still be beneficial.
F. Perry Wilson, MD, MSc, is an associate professor of medicine and director of the Yale Accelerator for Clinical and Translational Research. His scientific communication can be found in the Huffington Post, in the NPR and here in Medscape. He tweets @fperrywilson and hosts a repository of its communication work at www.methodsman.com.
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