For decades the vitamin industry has been promoting their products as generally good for health, and as a result 90% of the general public think taking vitamins is a good idea (although in the same survey 80% recognize that vitamins do not replace a healthful diet). A 2016 study found that 52% of the population take some form of supplementation. Use of multivitamins (MVI) did decrease a bit from 37% to 31% from 2000-2012.

Still, that is a huge portion of the general population. The supplement industry continues to grow every year, reaching $36.1 billion a year in the US in 2017. How much health benefit are we getting from that $36.1 billion? A new meta-analysis suggests – not much if any at all, and maybe even some harm. The new study, published in the Journal of the American College of Cardiology, is a meta-analysis of randomized controlled trials looking at a variety of vitamins, both multivitamins and specific vitamins, and their relationship to cardiovascular disease, stroke, and all-cause mortality. Because this is a recap of prior research, the results are not surprising to anyone familiar with that research.

What they found is that:

  • Multivitamins, vitamins D, C, A, B6, E, calcium, β-carotene, zinc, iron, magnesium, and selenium had no benefit or harm for vascular disease or all-cause mortality.
  • Folic acid and B-complex (Folic acid, B6 and B12) reduced stroke risk
  • Antioxidants and niacin increased all-cause mortality.

Or to show this visually:

All of these findings were supported by moderate level evidence. The most dramatic result was the reduction in stroke risk by folic acid (20%), however there is an important caveat to this finding. These results were largely driven by CSPPT (China Stroke Primary Prevention Trial). In most areas China does not fortify any food with folic acid, and therefore the population may be generally deficient. This benefit, therefore, may not translate to Western countries with fortification.

I have written about antioxidants before – the evidence shows that, not only are they of no routine benefit, they may cause harm by disrupting the natural mechanisms of internal homeostasis. The authors also note that while there was a clear benefit to folic acid, some studies show a potential increase in cancer risk (specifically prostate cancer, but this may extend to other cancers).

There are limits to this data. The quality of evidence was mostly moderate. Also, one could argue that longer term studies and larger studies might detect a smaller benefit. However, this data does set limits on the magnitude of any possible remaining benefit. Further, the exact same argument can be made about potential harms.

This meta-analysis is a good opportunity to step back and reconsider our basic approach to vitamins and supplements, in terms of both practical implications and underlying philosophy. In terms of philosophy, there are various assumptions (encouraged by the supplement industry, who stands to gain from these assumptions) that do not make sense when analyzed, and have not been supported by the evidence.

The first is that vitamins are all good. This stems further from the more fundamental approach to nutrition that there are good foods you should eat and bad foods you should avoid. Vitamins, in this view, are healthful in-and-of themselves. This leads to two further beliefs: that if some is good, more is better, and that vitamins can do no harm. In this view there is little downside and no risk to taking vitamins “as insurance,” even if they are not strictly needed.

This heavily marketed approach runs contrary to standard clinical logic, which recognizes that dose is everything, and all interventions should be looked at from the perspective of risk vs benefit.

Every vitamin has a toxic dose. Further, there is likely a ceiling effect, meaning that there is a level of intake that is sufficient and anything beyond that is of no further benefit. In this view, maximal nutritional benefit comes from taking the appropriate amount of each vitamin, rather than simply taking more. Most vitamins do have a very large range over which they are essentially harmless, which creates the false impression that all vitamins are completely harmless. Some vitamins have a narrower range, and it is possible to experience toxic effects from routine supplementation, or even from an extreme diet. Vitamins A and B6 toxicity are not rare. I have diagnosed B6 toxicity myself, which can cause nerve damage. There is also good reason to conclude that large doses of antioxidants can be harmful, supported further by the current study.

Aside from direct harm, there is the potential for even greater indirect harm. The $36 billion and growing supplement industry represents a massive opportunity cost for health care. Some people might forgo needed medications, or better nutrition, because they are spending some of their limited budget on vitamins and supplements they think will help them, but won’t.

Further, there is the potential of using supplementation as an excuse for an otherwise poor diet. The evidence clearly shows that vitamins do not replace a well-rounded and nutritious diet.

The bottom line message for the average person is this:

There is essentially no benefit to routine supplementation, and there may be some risks. You are far better off saving your money, and spending it on fresh produce. Have a varied diet with plenty of fruits and vegetables and you are overwhelmingly likely to get all the nutrition you need.

For those with special needs or if you have any questions, simply consult your physician. Targeted supplementation based on specific needs and measured blood levels is the way to go. You probably should be taking prenatal vitamins if you are trying to get pregnant, and should be under the care of an OB. If you are trying to reduce your stroke and vascular risk, again you should be doing this under the supervision of an appropriate physician. This may include folic acid supplementation.

Also, while we are at it – do not believe supplement hype (antioxidant or otherwise), do not believe nutrition gurus, do not take megadoses, and there is no such thing as a “superfood.”

Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.