I just gave a seminar with this title at Ohio State University: . I began by harkening back to 1985 when I was teaching my first intro nutrition course. I wondered how to fill 20 minutes for vitamin D. Fast forward to the last time I taught this same course. I wondered how I would manage to limit my vitamin D presentation to only 20 minutes. We had gone from vitamin D drawing minimal public attention to people flocking to buy vitamin D supplements.
Vitamin D can be obtained from a few foods and made in skin that is exposed to sunlight. Still, for many people, supplements end up being the prime source. Various people have all kinds of ideas about what the supplements can do and how much to take. In reality, the real research data is a tangled mess. Nonetheless, when I presented my seminar, I made some observations.
I am expanding the seminar content for a chapter in the book I am writing (The Authoritative Guide to Nutritional Supplements). Here is a Cliff Notes version of my current impressions:
• Conflicting research results are not surprising given the variations in people studied & other design aspects.
• The best effects of vitamin D probably occur when used as part of a general health plan; studies are not generally done that way (because they are hard to do and harder to get funded).
• We should think less about how much vitamin D to take and more about what serum/plasma readings to get; the amount to take to get those readings can vary among people and in a single person at different times.
• Some vitamin D benefits may tap out at 20 ng/ml serum or even below; others may need getting above 30 ng/ml.
• Some studies report benefits for higher serum levels; most of these studies have one of the following issues: design problems; not showing that the same benefits couldn’t occur with lower readings; getting only minor advantages with the high readings.
• I found a very few studies that at least raise the possibility of certain advantages for high readings.
• In contrast to the last statement, a number of studies show possible fall off for vitamin D supplement effectiveness as the doses or serum readings get too high.
• I also found reports of negative effects of high dose vitamin D supplements and/or high serum/plasma readings; these negative effects occurred at far lower supplement doses or serum readings than what produces “classic” vitamin D toxicity
At present, I lean toward telling most people to shoot for a reading in the low 30s ng/ml. This seems mostly safe and covers most benefits. The book chapter will give more details than I wrote here.