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It is my understanding that vitamin D intoxication from the sun does not occur because the body prevents further vitamin D production when it has enough. One issue is that this process is bypassed with supplementation, which makes vitamin D intoxication possible. Why not determine the optimum human 25OHD level by figuring out when the body halts production rather than inferring that level from less direct phenomenon?

Asked by  Andrew on August 12, 2015

  •  Andrew on

    See title

    Answered by  Andrew on
  •  Amber Tovey on

    Hi Andrew,

    You are correct that sun exposure cannot cause vitamin D toxicity. We actually determined our recommended range from looking at the vitamin D levels of hunter gatherers who live within a few degrees of the equator. Humans are meant to be sun loving creatures. Thus, from an evolutionary perspective, the vitamin D levels of those who spend every day out in the sun would reflect the optimal 25(OH)D level.

    The study from 2012 looked at the 25(OH)D levels of 60 pastoral “hunter-gatherers” (35 Maasai and 25 Hadzabe). Their average vitamin D status was about 50 ng/ml. That is why we recommend a range between 40 and 80 ng/ml.

    Here is a link to a blog that Dr. John Cannell wrote on the paper: http://www.vitamindcouncil.org/blog/vitamin-d-status-in-indigenous-populations-part-1/

    Amber Tovey

    Answered by  Amber Tovey on
  •  Andrew on

    Hi, and thanks for the reply.

    I understand all that – ancestral range inferred by measuring contemporary hunter-gatherers, summer lifeguards and outdoor laborers, that “high” 25OHD is required for D in breast milk or deposition into fat, the interplay of D levels with thyroid hormones, etc. I agree there is a lot of data we can use to infer optimum 25OHD.

    I guess I’m wondering why we haven’t (or can’t) more directly determine that value or range, and do that by figuring out at what level the body shuts down its production of vitamin D from the sun. It seems to me having a hard UL backed by “because that’s where the body shuts off production of D from sunlight” would be of enormous value – much more than “we see no evidence of toxicity”.

    I think knowing that the body shuts down vitamin D production when the level reaches X Y or Z would give people a better idea of the natural ceiling, a better target for supplementation, and therefore more peace of mind. If you want people to feel more at ease about taking 10x or 20x the RDA, I think this would be it. “We see no signs of toxicity” is good but “the body shuts down production here” seems better, imho.

    Answered by  Andrew on

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