Doctor's Note

This is the second in a nine-part series on vitamin D. Be sure to check out yesterday’s video: Vitamin D Recommendations Changed.

For more context, check out my associated blog posts: Vitamin D: Shedding some light on the new recommendations, and Vitamin D from Mushrooms, Sun, or Supplements?.

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  • Michael Greger M.D.

    Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. This is the second video in a nine day series on vitamin D. Be sure to check out yesterday’s video-of-the-day Vitamin D recommendations changed.

  • CapeBreton

    Interesting topic. I assume the lifeguards were caucasian? With a “built in” SPF of 15 what blood level of Vit D does the lifeguard of African descent attain? Perhaps that is a better clue for evolutionary “normal”.


      I think this is a clue to get more direct sun exposure without burning. This is what we tell our dermatology patients. Supplement this video out with this next one:

      There defintely are some puzzling and confusing outcomes on vit d studies. I think that the body is capable of monitoring how much vit. D a body produces depending on its need. I hope that soon some study will unravel the mystery that shrouds vit. D absorption.

    • Michael Greger M.D.

      You’re absolutely right, CapeBreton. Considering the average vitamin D levels of clothed high latitude office workers “normal” for our species doesn’t make much sense and though lifeguards are at least outside all day and half naked, they were still both Caucasian and Missourian. A more representative normal level of the “sunshine vitamin” could be gleaned measuring levels in those with black skin who live scantily clad in equatorial Africa. The problem is that such a study has never been done–until now.

      This month researchers published results from the Maasai and the Hadzaben and the title says it all: “Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/l.” So lower than the pale St. Louisans, but still nearly twice the levels found in most Americans. No change to my recommendations, though, summarized in the culmination of my two week vitamin D series: Resolving the vitamin D-bate.

  • filippodibari

    Hi Dr Greger, your attention to Vitamin D is very relevant these months also to the huge discussion about the use of Vitamin D supplementation in Tubercolosis in developing countries. My best regards. fil

    • Michael Greger M.D.

      Vitamin D is thought to be why the TB sanatoriums of old proved effective. They used so-called “heliotherapy,” which just meant exposing people to sunlight, 62 years before vitamin D was even discovered. Once vitamin D was identified and purified it was used therapeutically both before and after antibiotics were introduced.

      There is evidence that vitamin D supplementation may help prevent other respiratory diseases as well. For example, one study found that those randomized to 2000 IU of vitamin D a day (the amount I recommend) appeared to reduce their incidence of colds and the flu by 90%.

      The official vitamin D recommendation recently tripled to 600 IU (see Vitamin D Recommendations Changed), though the Endocrine Society just released guidelines suggesting 1,500-2,000 IU a day is better. To offer some insight into the behind-the-scenes wrangling on this issue I’m in the process of rolling out a 9-day series of videos on the topic that will finish up this coming week. I’m always conflicted about the level of depth I should go into on individual topics. I’d love everyone’s feedback on whether they prefer the one-off 2 minute highlight-type videos or these longer series where I delve deeper into the back-story.

      • Love the video about the Lifegaurds! I only volunteer once very 3 weeks though!

  • Dear Dr Greger,
    thanks for this. Few comments.

    – 2 min vs. longer: maybe the two are good for two different targeted audience? 2 min meant to be for lay people interested AND longer designed for both very interested people + professionals.

    – After all, also people like me, Public Health Nutrition professional, enjoy both strategies: the 2 min gives me a good grasp about new studies on the topic. I can always go back to it and research more.

    – If longer videoclip is there, than it is a joy to learn from it. Referencing for my own work becomes so much easier. Your work is valuable because spare the time to contstantly keep looking at the latest journal issue on so many topics.

    Therefore thanks for that.

    Please, let me dare to hint something for future videos. If spreading evidence-based nutrition is part of your mandate/mission/passion, maybe it would be interesting for your audience:

    – to learn just a little bit about the few different strength level of the available studies on nutrition (at least RCT vs. observational, plus case control,etc.). Objective: to appreciate the different quality of evidence out there. The beauty of this would be that you could always refer to such a video, just saying “this is a strong piece of evidence” or “this is not…” and then referring to this previous video. There is a good review on strenghts ranking for nutrition studies on the latest FAO fatty acids (

    – to learn about the differnt strategies to search on specific topics nutrition related. I do it regullarly not only for my job but ALSO for my own diet or friend’s diet, just a guidance or food-for-thoughT. That could be done based on open source data base (PubMed or other). I am sure people would still follow you pretty much, even if they set up their own email alerts on Pubmed web site. The “Limits” filter is one of my best friends there.

    Then a final question: will you ever tackle the topic of ready-to-use-foods (termed also lipid-base nutrients supplements) to prevent and treat malnutrition in emergency contexts or in very poor countries? Among the latest ones:

    The topic is picking up. The World Bank estimates that each year about USD 6.2 billion are needed to treat 3.5 million under five children affected by severe ( or moderate acute malnutrition ( If not treated on time, these might represent more than one-third of all paediatric deaths worldwide ( A large coalition of international institutions is currently engaged in raising the needed funds (

    I am sorry if my message is far too long.

    My best regards and thanks for your very interesting work.

    Filippo Dibari

  • DrDons

    To add to the discussion. I agree that Dr. Greger should vary the number of videos depending on the topic. Vitamin D is an example requiring multiple videos. I think grouping them together helps. Thanks for the heads up on Vit D and TB. I found looking into the topic interesting. Dr. Greger’s points are excellent. It is of note that the TB incidence began to fall before the use of AntiTB drugs so we have alot to learn about non medicinal treatments. I enjoy reading the science as we look to find the “magic” bullets for treating disease. However I would like to see us effectively work on the “upstream”(see Dr. Ardell’s fable, Upstream/Downstream) issues that would help with primary prevention. In the case of TB issues such as the reduction of poverty and overcrowding. Going further we need to stem the Era of Infectious Disease which if the Bird Flu takes off will make the TB situation look mild by comparison. If you haven’t read I would suggest Dr. Greger’s article in Critical Reviews of Microbiology, 2007 for the best review of the Human/Animal Interface… including the origin of TB and his book on Bird Flu which is available for free reading on line.

  • Michael Greger M.D.

    For some context, please check out my associated blog post Vitamin D: Shedding Some Light on the New Recommendations!