Scientific evidence for supplements and snake oil

Some dietary supplements, nutraceuticals, vitamins and antioxidants are proving their efficacy in clinical trials and research for specific conditions, others are unadulterated snake oil. Information is Beautiful posted a pretty, but relatively unscientific, animated bubble chart to show where each supplement might sit in the sphere of health for a given condition. Needless to say, I shared the page on Twitter and Facebook and see that it’s had well over 4500 visits.

The site claims the chart is a representation of the scientific evidence for supplement efficacy for healthy adults on a good diet, apparently. Bubbles that float to the top are apparently those with more PubMed and Cochrane citations for a given supplement-condition. Bigger bubbles, means more Google hits.

Dietary supplements or snake oil

A clinical friend pointed out that folic acid is shown as having only “good” evidence; whereas it is a standard prescribable medication. Folic acid/folate is standard first-line pregnancy advice and on FP10 prescription and has been for a long time to combat neural tube defects. One would have assumed that this would have been based on ‘strong’ rather than just ‘good’ evidence.

Of course, good to strong evidence is pretty much all prescription medications get. There is no proof in science.

Bruce Head also pointed out some other problems with the bubbles. “I find the chart interesting but confusing. Some supplements are showing up equally in the ‘strong evidence’ area and BELOW the ‘worth it’ line – for the same condition. For example, check ‘Cancer’ and ‘All types’ and ‘Selenium’ appears in both areas. Similar with ‘Mental Health’ and ‘Omega 3’,” he says.

It’s also worth noting that there are seemingly no magic supplements for sex, despite those ads in the back of the magazines and in your spambox. Glucosamine shows up as conflicting evidence for pain, whereas a whole range of supplements like acai, silica, taurine, wheat grass, dandelion, cranberry etc have no evidential links either way (pro or con) to any conditions. Green tea is below the worth it line for cancer in general and close to the bottom (no evidence) for breast and prostate cancer, and weight loss. Similarly, not a lot of proof that probiotics protect against colon cancer and no good evidence for black cohosh in menopause treatment. It’s a mixed picture.

I suspect the bubble chart is not quite as scientific as it might seem, especially if it’s based on a loose PubMed and Cochrane citation count and Google hits, rather than a conventional meta analysis of the data. I would always suggest taking anything like this with a pinch of salt…although salt should of course be above and below the line for cardiovascular and dehydration cramps, so not too much now.