Michael Greger MD

Michael Greger MD

Posted October 16, 2011

Published in Health

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Ask the Doctor: Q&A with Michael Greger, M.D. (Week 5)

Read More: alfalfa sprouts, broccoli, broccoli sprouts, cruciferous, greens, hormones, infertility, iodine, kale, kimchi, licorice, sodium, soy, tanning beds, thyroid, vitamin D, vitamin D2, vitamin D3

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This is just a sampling of the over 600 comments and questions I've responded to on (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 make sure you don't miss any:

Eric Needs asked on Soy Hormones & Male Infertility: I've heard that soy can suppress the thyroid. Is there an upper limit?

Excellent question! Soy does indeed have so-called "goitrogenic" compounds (as does broccoli-family vegetables and flax seeds), which can interfere with thyroid function in people with marginal iodine intake. The answer is not to avoid these super healthy foods but to just make sure you get enough iodine. See my video Avoiding Iodine Deficiency.

evergreen517 asked on Vitamin D Pills vs. Tanning Beds: Now that there is a new vegan D3, (Vitashine) would you recommend this over D2? How much should we take per day? At 20$ a bottle, 4000 would be pretty expensive.

There is no advantage to taking D3 over D2 at the daily doses typically recommended. See my recommendations here: . I have lots of new videos on vitamin D coming up. If you can't wait, you can get a sneak peek on my new volume 6 Latest in Clinical Nutrition DVD (all proceeds to charity).

ksk63 asked on Is Licorice Good For You?: Does this also include the tea that I love to drink if so I will stop.

That is a great question. The only study I was able to find looked at a tea which included licorice root and concluded: "One cup of the herbal tea ["Smooth Move"] contains approximately 15 mg of glycyrrhizic acid, which is significantly below the level of concern for known side effects of licorice overdose."

tbarron asked on Update on Alfalfa Sprouts: What about alfalfa sprouts that we grow ourselves? Are the seeds contaminated (so sprouts I grow at home will be too), or is just sprouts offered by restaurants that needed to be avoided?

Excellent question! Turns out it appears to be contamination of the sprout seed itself, and so even if we sprout them ourselves we may be putting our family at risk. The answer? Sprout broccoli sprouts instead. Safer-and healthier too! They are kind of pungent, though. If anyone has found a good way to incorporate broccoli sprouts into their diet please share!

aeason asked on Is Kimchi Good For You? Is there more information about this? Is this traditionally made kimchee rather than kimchee made in a manner similar to that of making sauerkraut? For that matter what about sauerkraut and other pickles?

This was for traditional kimchi. I can't find anything in the literature about sauerkraut either way, but I'll definitely keep an eye out. It is high in sodium, so if you do eat it I would suggest moderating your intake.

walfaro asked on Overdosing on Greens: Do you consider 10 cups of cruciferous too much a day? Is there a link between them and inflammation?

According to this study published in the Journal of the Science of Food and Agriculture, 10 cups a day on a regular basis is probably the limit for raw kale-my second favorite vegetable!