Welcome to Impact Factor, your weekly morsel of commentary on a new medical study. I'm Perry Wilson.
How do you tell what a nephrologist thinks of vitamins? Don't worry, they'll let you know.
Yes, nephrons like me are fond of telling people that taking vitamins gives you expensive pee, but it's nice to see our flippant attitude bolstered by some real science, as seen in this study appearing in the Annals of Internal Medicine,[1] which suggests that taking vitamins has no effect on overall mortality.
Researchers examined data from about 31,000 individuals who were part of the National Health and Nutrition Examination Survey (NHANES). Participants in NHANES complete a variety of questionnaires that capture vitamin and supplement use, as well as a dietary recall to get a sense of what they are eating.
The researchers linked those responses to overall mortality to explore whether vitamins and supplements prevent death, and if so, which ones.
Now, people who take vitamins may be subject to what is known as the healthy-user effect. They are much more likely to do other healthful things, too. Just over 50% of the population was taking at least one vitamin or supplement, and there were quite a few differences between the users and non-users.
Those who partook of encapsulated nutrients tended to be older, more often female, more often white, more highly educated, and less likely to smoke or drink alcohol. They also had a higher "healthy-eating index," meaning that their regular diet was of better quality as well.
But the vitamin users did have more comorbid conditions; 12% had a history of cancer compared with just 6% of the non-users. The authors suggest that this could be due to individuals with chronic conditions taking their health into their own hands. I think it's also likely that once you are taking a prescription medication, the threshold to add a pill on another day is not such a high bar to cross.
After adjusting for all of these differences, the authors found... basically nothing.
Copyright 2019 American College of Physicians. Published with permission.
Out of 43 vitamins and minerals studied, only one—lycopene—seemed to have any protective effect. Don't get excited, ketchup lovers. Because of the multiple vitamins tested, there was around a 90% chance that at least one would pop up as a false positive.
So, vitamins don't do anything.
But—plot twist—food does. When the authors looked at the food diaries, they were able to tell who was getting adequate intake of 22 nutrients, like niacin, of which nearly 100% of the population has adequate intake, or fiber, of which nearly 100% do not have adequate intake.
Two nutrients appeared to be protective in terms of all-cause mortality: vitamin K and magnesium—but only if you got them via food. Here's a comparison of the food-intake benefit of these nutrients compared with the benefit you get from supplementation.
Here's the thing: This study doesn't show us that there is something magical about getting these nutrients in food compared with the pill form that makes them protective. None of these nutrients are likely doing anything. Sure, if you have a severe deficiency of something, the nutrients help; but no one in this study had scurvy or beriberi or even rickets. If eating more vitamin K is better, we should see a signal from the supplements.
That we don't teaches us an important lesson. Dietary research that purports to link a single nutrient to an important outcome is often hopelessly confounded by the strong relationships between the intake of that nutrient and all of the other things you put in your body and do for your body.
People who get more vitamin K from food live longer not because they eat more vitamin K but because they eat a host of things—like green leafy vegetables—that correlate with vitamin K. Vitamin K is just a stand-in for a whole package of behaviors.
What's a clinician to do? Don't encourage your patients to eat more vitamin K or magnesium. Encourage them to eat good, nutritious foods and to engage in all of the healthful behaviors, like regular exercise, that really drive these observed benefits.
Medscape © 2019 WebMD, LLC
Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.
Cite this: Will Eating These Nutrients Lower Mortality? - Medscape - Apr 10, 2019.
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