But I thought it would save you...

Before I studied medicine, I used to have an inner monologue that went somewhat like “If I don’t eat enough healthy foods I might get cancer, so tomorrow I have to eat more carrots”.  I would hear the headlines about the next thing that might save you and think, OK, let’s do this.  A couple of experiences have tempered my enthusiasm to jump on the next new healthy thing.  I want to write about some of those here. During my residency, my father-in-law was diagnosed with prostate cancer. (Don’t worry, he is just fine now.) At the time, I was a bit spooked.  In addition to my concern for my father-in-law, I worried about what this meant for my husband?  What could I do to keep him from having the same outcome?  A mentor of mine had mentioned that there was “good evidence” that selenium could help prevent prostate cancer.  So, I headed out to the health food store and brought home this wonderful preventive pill for my husband.  I reminded him every day to take it, feeling satisfied that I had control of the situation.  Then, in 2008 the SELECT trial, a high quality study intended to really tease out if selenium saved people from prostate cancer, found that it really wasn’t helping and that it increased the risks of diabetes.  I threw away the pills and promised I wouldn’t make my husband a guinea pig again.  In 2014 further results from the SELECT trial showed that selenium supplementation actually increased the risk of more aggressive prostate cancer in men who had high levels of selenium to begin with.  So, I was actually poisoning my husband. Oops.

This same story has played out with other popular supplements.  Let’s start with a discussion about beta carotene.  Beta carotene is a natural pro-vitamin A, it's synthesized in the body into vitamin A.  It's the nutrient we often attribute to the bright color of various fruits and vegetables. People who self-reported a diet that included relatively large amounts of food rich in beta carotene and other carotenoids had a lower risk of lung cancer.

Then they took the next step and tested blood levels of beta carotene and watched to see what happened to people’s health as they aged.  They found that people with the higher levels of beta carotene had a lower incidence of lung cancer, heart disease, other cancer and all-cause mortality (any cause of death).  So based on this, you would be ready to bring this pill home to your spouse, right?

This data, which is very often picked up as headlines and recommendations represents only the start of our scientific process.  These observations and monitoring are meant to help us formulate the right questions, but not to find the answers. The answers are meant to be found in much more rigorous scientific studies, called randomized controlled trials and meta-analyses.  Where large groups of people are randomly assigned to either take a beta carotene supplement or to take placebo then we monitor to see what happens.  This is a great resource for understanding more about the levels of evidence based medicine.

The ATBC trial which took place from 1985-1993 did just this.  They took about 30,000 Finnish male smokers and gave them a supplement for 5 to 8 years containing beta-carotene, vitamin E, both, or a placebo.  What they found in the initial data was that the people taking the beta carotene had an 18% increase in lung cancer and an 8% increase in overall mortality (all causes of death).  When they looked at these men 8 years later they found a 7% increase in overall mortality.

Now this is just one randomized controlled trial and it should be said that even though it is more powerful than the observational studies, it still doesn’t necessarily represent the TRUTH.  But, it helps point the ship in a different direction and it does make it fairly clear that if you are Finnish male who smokes, taking a beta carotene supplement is probably a bad idea.  In 2007 a systematic review and meta-analysis (these are the best science we have), showed that treatment with beta carotene, vitamin A and vitamin E may increase mortality.

Based on this, I recommend a bit of healthy skepticism with sensational headlines and patience with the scientific method.

... More to come on Vitamin D.