Vitamin D Not A Panacea For Most Medical Conditions Interview with:

Michael Allan, MD CCFP Professor of Family Medicine and Director of Evidence Based Medicine Faculty of Medicine & Dentistry University of Alberta

Dr. Mike Allan

Michael Allan, MD CCFP
Professor of Family Medicine and
Director of Evidence Based Medicine
Faculty of Medicine & Dentistry
University of Alberta What is the background for this study?

Dr. Allan: A large volume of observational (lower-level) research links lower Vitamin D levels with a long list of health concerns. Other non-clinical studies show the biochemical and physiological actions of Vitamin D could impact many health states. These factors have led many clinicians and scientists to advocate strongly for Vitamin D supplementation. However, this type of research can draw false connections. Therefore, we must examine high-quality randomized studies to determine if Vitamin D supplement can help people live longer, have improved health or avoid negative health outcomes. What are the main findings?

Dr. Allan:  We examined 10 specific areas, considering only the highest-level evidence. There is some evidence that regular use of Vitamin D ≥800 IU, with calcium (perhaps around 500mg), will reduce fracture risk. For example, if your chance of fracture was 15% over 10 years, taking vitamin D and calcium would reduce the risk to around 13% over 10 years. Vitamin D supplementation probably reduces the risk of falls in those at highest risk but the evidence is less reliable. Mortality may also be reduced but, if real, the difference would be small. For example, if a person has a 10% chance of dying in 10 years, taking Vitamin D every day for 10 years may reduce that risk to 9.5%. These positive effects were generally derived in populations over age 50 and most are over 65. There was no reliable or consistent evidence that Vitamin D prevents cancer, rheumatoid arthritis, or respiratory infection. There was also no reliable or consistent evidence that vitamin D improves multiple sclerosis, rheumatoid arthritis or depression/mental well being. Furthermore, mega-doses (≥300,000 IU taken once in autumn) seem to increase falls and/or fractures. Lastly, evidence does not support testing Vitamin D levels in the general population. What was most surprising?

Dr. Allan:  Much of the research was poor quality or had significant limitations. For example, of 11 randomized studies on low mood/depression, eight allowed inclusion of patients who were not depressed. What should readers take away from your report?

Dr. Allan: Vitamin D may still be appropriate for older patients (example ≥50 years old), particularly those willing to take medicines for small reduction in fracture risk or those at high risk of falls. For younger adults, Vitamin D likely provides no meaningful or measurable benefit in health. Is there anything else you would like to add?

Dr. Allan: Clinicians and patients should be aware that while lower-level evidence presents some compelling justification for regular Vitamin D supplementation, the potential benefits may be limited to small changes in falls and fractures for those at risk. Unfortunately, high level evidence fails to show convincing proof Vitamin D can have a meaningful improvement of health for adults. Thank you for your contribution to the community.


G. Michael Allan, Lynda Cranston, Adrienne Lindblad, James McCormack, Michael R. Kolber, Scott Garrison, Christina Korownyk. Vitamin D: A Narrative Review Examining the Evidence for Ten Beliefs. Journal of General Internal Medicine, 2016; 31 (7): 780 DOI: 10.1007/s11606-016-3645-y

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.

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1 Comment
  • Count Iblis
    Posted at 21:38h, 20 June

    RCTs are only good for testing drugs that given the prior evidence,are unlikely to be useful for the body except possibly for a few medical conditions that are the focus of the RCT. E.g. statin drugs will a priori be tested for cholesterol levels and the effect on cardiovascular disease. The end points of such studies are a priori well defined.

    Contrast this with studying vitamin D. We know that vitamin D receptors exists in many different tissues, it is clear that vitamin D is involved in many different processes, only a few of these have to do with bone health. This does not mean that vitamin D is useful as a high dose supplement, but it does make it difficult to get to the bottom of the health effects of vitamin D supplementation.

    If a priori there is no good reason to only look for just a limited set of health outcomes, it’s not possible to say that just because some given health outcome didn’t yield positive results that vitamin D supplementation is most likely useless. A more reasonable approach i.m.o. is to consider what natural levels of vitamin D are, studies done in indigenous communities in Africa (Hadzabe and Maasai people) show that their calcidiol levels are around 120 nmol/l. Then we should just accept this as a normal level, if we were living the way people a few centuries lived (not sitting for hours inside offices but working outside) we would have similar calcidiol levels.

    Then health effects due to having lower calcidiol levels of 50 nmol/l may be unhealthy, and it should be rigorously proven that such lower levels are not putting people at risk. We know that going below 50 nmol/l is not good for bone health, but absence of proof of benefits of going above 50 nmol/l is not proof that 50 nmol/l is better than 120 nmol/l.

    There exists tentative evidence that higher levels help with recuperation from hard exercise. Such indirect effects may explain some of the evidence regarding positive effects of vitamin D that were later not found in more rigorous RCTs. If vitamin D were to help people to stick to a strenuous exercise routine (and then if you can keep on exercising outside the vitamin D you get from being outside longer would help you maintain this routine) then it could be that it’s the fitness gained from exercising more, not the vitamin D that explains the results. But the role of vitamin D is then still nontrivial, take away the vitamin D and you may not have been able to stick to the exercise routine.