Why do vitamins keep on failing in clinical trials?
Hopes that vitamin supplements can fend off cancer, cognitive decline, and other health problems keep on getting dashed. The arc is pretty familiar. Epidemiologic studies, often with animal experiments and lab-based research thrown in, suggest protective effects. But results from randomized clinical trials show no effect. The bubble of optimism pops, and the public attitude toward nutrition science and advice sours.
There are several explanations for why this happens. People inclined to take vitamins often have good health habits, and those health habits, rather than the vitamins, may be responsible for the positive effects seen in epidemiologic studies, despite good-faith efforts (and fancy statistical techniques) used by researchers to separate them out. Vitamins in food may be one thing, vitamins in pill form, another. Short trials may not last long enough for vitamins to have a pronounced effect on some of the diseases being studied. And in longer ones, compliance with taking a test nutrient often falls off, diminishing the contrast with the control group and increasing the chances that the results won't show any difference between those who took the nutrient and those who didn't.
To continue reading this article, you must log in.
Subscribe to Harvard Health Online Plus (HHO+) to unlock expert-backed health insights, personalized tools, and exclusive resources to feel your best every day.
Here’s what you get with your HHO+ membership:
- Unlimited access to all Harvard Health Online content
- 4 expertly curated newsletters delivered monthly
- Customized website experience aligned to your health goals
- In-depth health guides on topics like sleep, exercise, and more
- Interactive features like videos and quizzes
- Members-only access to exclusive articles and resources
I’d like to subscribe to HHO+ for $4.99/month to access expert-backed content to help make smart, informed decisions about my well-being.
Sign Me UpAlready a member? Login ».
Disclaimer:
As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles.
No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.
