You go on to say that pale skin is evidence of selection pressure in favor of keeping vitamin D at this high level, suggesting health issues at lower levels. That seems plausible to me, but I want to consider another possibility, which is that issues from lower vitamin D levels may occur specifically in pregnancy.
Looking at Luxwolda et al 2013, it’s 107 nmol/L among non-pregnant adults, and 136 nMol/L among pregnant women. Confidence intervals are wide, though pregnancy was significant in their regression, with an effect of +40 nmol/L, confint (29, 52).
I guess we already know it’s more important in pregnancy. I just bring it up because it may undermine the evolutionary speculation. You do mention:
Some might argue that the purpose of fortification is to reach the severely deficient, or children, the elderly or pregnant mothers. Maybe!
The same reasoning you’re applying to whoever’s fortifying food, apply it to natural selection. The need for very high levels in pregnancy may be sufficient to explain adaptations for keeping levels high (such as pale skin), even in the absence of harms at lower levels in non-pregnant adults.
Of course this is itself just more evolutionary speculation, but it’s good to keep multiple possibilities in mind while speculating; the absence of evidence that would uniquely pin down one possibility is what makes it speculation.
Yeah, I totally agree. It’s entirely possible that the vitamin-D / folate hypothesis is true, but the benefits of vitamin D come in ways that wouldn’t impact all-cause-mortality. I sort of hinted at things along this line with “even if true, might be driven by severe deficiency and rickets” but maybe I could do a better job of reflecting that there could be other things on that list.
You go on to say that pale skin is evidence of selection pressure in favor of keeping vitamin D at this high level, suggesting health issues at lower levels. That seems plausible to me, but I want to consider another possibility, which is that issues from lower vitamin D levels may occur specifically in pregnancy.
Looking at Luxwolda et al 2013, it’s 107 nmol/L among non-pregnant adults, and 136 nMol/L among pregnant women. Confidence intervals are wide, though pregnancy was significant in their regression, with an effect of +40 nmol/L, confint (29, 52).
I guess we already know it’s more important in pregnancy. I just bring it up because it may undermine the evolutionary speculation. You do mention:
The same reasoning you’re applying to whoever’s fortifying food, apply it to natural selection. The need for very high levels in pregnancy may be sufficient to explain adaptations for keeping levels high (such as pale skin), even in the absence of harms at lower levels in non-pregnant adults.
Of course this is itself just more evolutionary speculation, but it’s good to keep multiple possibilities in mind while speculating; the absence of evidence that would uniquely pin down one possibility is what makes it speculation.
Yeah, I totally agree. It’s entirely possible that the vitamin-D / folate hypothesis is true, but the benefits of vitamin D come in ways that wouldn’t impact all-cause-mortality. I sort of hinted at things along this line with “even if true, might be driven by severe deficiency and rickets” but maybe I could do a better job of reflecting that there could be other things on that list.