Michael Greger MD

Michael Greger MD

Posted February 9, 2012

Published in Health

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Ask the Doctor: Q&A with Michael Greger, M.D. (#18)

Read More: algae, astaxanthin, BPA, canned vegetables, celery, chlorella, colon cancer, fish, fluoride, pesticides, phytonutrients, spirulina, supplements, vaccination, vitamin D, water

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This is another sampling of the more than 800 comments and questions I’ve responded to on the site (so far!). Please feel free to leave any follow-up questions here or on any of the hundreds of videos on the more than a thousand topics covered on And remember, there’s a new video posted every weekday, so to make sure you don’t miss any:

CapeBreton asked on Evolutionary argument for optimal vitamin D levelI 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”.

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.

Toxins asked on Ask the Doctor (#16)Dr. Greger, I have heard some talk about the dangers of fluoride. When I research this all I stumble upon are propagandists websites without scientific backing. Is there any truth to these claims that fluoride in our water supply and toothpaste is damaging our health?

The proposed EPA changes to water fluoridation have sparked a resurgence of many of the old anti-fluoridation arguments, which as far as I can tell were successfully debunked over 50 years ago. According to the CDC, fluoridation of drinking water joins vaccination (another unjustly vilified practice) as one of the greatest public health achievements in the last last century.

MarkB asked on Dragon's bloodIs any research available on astaxanthin which seems to be touted as a wonderful antioxidant?

Astaxanthin is the reason flamingos are pink (or at least flamingos in the wild; in the zoo they may be fed artificial dyes like farmed salmon–see my video Artificial Coloring in Fish). Astaxanthin is also the reason some crustacean shells turn red when boiled. One need not eat flamingo feathers or lobster exoskeletons, though. You can go right to the source and get it from green algae such as chlorella (I recommend against blue-grean algae and spirulina–see for example my videos Is blue-green algae good for you? and Another Update on Spirulina). A review last month suggests a wide range of beneficial effects, though one should note the author is listed as a dietary supplement industry consultant. With a few exceptions, I recommend against taking supplements as they have been found in some cases to be less effective (see, for example, my Produce Not Pills) or even deleterious (see Is vitamin D the new vitamin E? and my other 60 videos on supplements).

Georgel asked on Ask the Doctor (#17):  I’ve seen a number of blog posts about some food scientists stating that if you avoid ANY food, canned tomato products and non-organic root vegetables should be at the top of your list?  Do you know anything about these statements? Is it just the opinion of a few researchers or is there a lot of weight behind the recommendation to avoid those products?

Did they offer any rationale? With canned tomato products are they concerned about the BPA? (see my video Which Plastics are Harmful?). A recent study found that it was canned tuna that had the highest levels, whereas concentrations in canned vegetables was relatively low. And pesticides in root vegetables? Only one even made it into the Environmental Working Group’s top twenty list. If I had to pick a worst food it would probably be Crisco, processed meat, or some of the mentions in my blog post about Paula Deen.

Joanne Irwin asked on Ask the Doctor (#16)Class participant heard that celery should be avoided for colon cancer patients. Only thing I’ve read about celery is to consume only ‘organic’ as conventional grown veggie is extremely high in pesticides. Do you know any other reason it should be avoided?  Thanks.

Celery avoidance makes no sense to me. In fact celery may have a “strong protective effect against colorectal cancer.” And in terms of for people already fighting the disease, a study was just published a few weeks ago elucidating the mechanism by which one of the key phytonutrients in celery (luteolin) arrests the growth of human colon cancer cells in vitro. For a comparison of the anti-cancer activity of a variety of vegetables, see my videos Veggies vs. Cancer and the follow-up, #1 Anticancer Vegetable.

For some reason the subject of nutrition appears especially wrought with myths, exaggerations, and baseless opinions. That’s in fact one of the reasons was started. When it comes to what we put in our bodies, critical thinking is, well, critical. Any time anyone hears anything like that I would encourage you to ask what their source was for their information. If there really is science backing up their assertions I’d be happy to review it and offer my thoughts.

-Michael Greger, M.D.