Vitamin D Gets a DownshiftJanuary 20, 2014
|Vitamin D Gets a Downshift|
|Reference: Neal Binkley in JCEM
What a life! At least 28.9 hours a week on the beach in Hawaii. Got any volunteers this time of year in Wisconsin? That’s who Neal Binkley and Bruce Hollis went looking for to investigate what Vitamin D level do we get in the most sun-soaked Caucasians he could find. They found 90 adults. Binkley and Hollis are some of the strongest advocates for D in the country.
Binkley is at U of Wisconsin and first broke the door open with his seminal study of low D in Wisconsin with a seasonal variability. They were interested to find what happened to “white guys” when they hang out in the sun a lot. What would you guess the mean level of D would be? It was 31.6. The very highest was 62 ng. If insufficient D was below 30, then half the folks in this study were insufficient, despite have intense deep, dark tans and abundant exposure.
Now, there could be many reasons for this seemingly low number. Sunblock works. The study was done during Hawaii’s “winter” though one might chuckle at that concept. Not everyone surfs at the height of the day with the most intense sun exposure. Late afternoon is much nicer if you are a surfer and get out of bed at 1 pm. Sun is going down then and you don’t get as much D. But the real reason may be just because, that’s the way it is. There may be more variability in making D in the human population that we perceived.
My prior report from Tanzania with Africans living right on the equator showed a higher range with D leveling out around 50-55 average. Why would some folks have lower D? Skin pigment is a necessary ingredient to protect circulating folate. Dark skin makes sure folate is protected from UVB radiation. Light skin and your folate gets fried when you spend lots of sun time. Maybe a deep tan is a problem and too efficient at blocking UVB radiation.
Or maybe there are other ideas that we just haven’t thought of yet. For example, all the association studies of Vitamin D being associated with illness may be backward. Maybe the disease consumes the Vitamin D, leading to a lower level and not vice versa. It does raise the question as to whether we should have an upper limit of D being 100 when you can’t get humans that high, no matter what. That limit was set on the hypothetical grounds that PTH (parathyroid hormone) keeps dropping until you get to 100. Now, high PTH is always bad. It affects many organ systems, all badly. The less PTH you have, the better. At least that was the word on the street. When Dror reports in JCEP that 20-36 is the range of lowest cardiovascular risk, with risk above and below, we have to sit up and listen. There were plenty below (insufficient) but the concept that there is risk above a certain limit is new.
Nature has many “J-shaped” curves with an optimal "middle" range. These two papers together make a compelling argument to revisit the safest range.
WWW. What will work for me? I’m pushing a reset button. New research showing risk at the top end is unexpected, but that’s what research does. Sounds to me like 30-40 might be my new goal. I know you don’t make cathelicidin (your natural internal antibiotic) below 32. So which risk do you want? But I’m backing off 60-80 for sure and instead of 5000 a day, we might all want to drift down a bit and do that 5000 pill 4 times a week so you get 3000 a day. 2000 a day and you end up at 29, on average. Oh bother, forget it all. Tickets to Hawaii are still available. Spend 29 hours this next week…..on the beach.