The August issue of The American Journal of Clinical Nutrition, has a supplement of articles, Vitamin D and Health in the 21st Century Update. ScienceDaily has some quotes from one of the main researchers:
... Norman identifies vitamin D's potential for contributions to good health in the adaptive and innate immune systems, the secretion and regulation of insulin by the pancreas, the heart and blood pressure regulation, muscle strength and brain activity. In addition, access to adequate amounts of vitamin D is believed to be beneficial towards reducing the risk of cancer.
I think a focus on the immune system is important from an evolutionary perspective.
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CHICAGO (AP) -- The nation's leading pediatricians group says children from newborns to teens should get double the usually recommended amount of vitamin D because of evidence that it may help prevent serious diseases.
To meet the new recommendation of 400 units daily...
I lack access to these papers today, so maybe I am repeating their contents, but there has been some talk about maybe raising the recommendation above 400 IUs. (This is in addition to the recommendation for youths, which actually has been changed as Hank R. just said.) E.g., this NIH document:
In March 2007, a group of vitamin D and nutrition researchers published a controversial and provocative editorial contending that the desirable concentration of 25(OH)D is â¥30 ng/mL (â¥75 nmol/L) [12]. They noted that supplemental intakes of 400 IU/day of vitamin D increase 25(OH)D concentrations by only 2.8-4.8 ng/mL (7-12 nmol/L) and that daily intakes of approximately 1,700 IU are needed to raise these concentrations from 20 to 32 ng/mL (50 to 80 nmol/L).
This study of postmenopausal white women in Nebraska, which importantly is interventional not observational, got particular attention if I recall: http://www.ajcn.org/cgi/content/full/85/6/1586?
The effect size is striking, so this study is big news if indeed it is gospel. IMO, it kinda needs to be confirmed, because the p-val is not that striking. Especially since there is a highly logical, but probably ex post facto data massage that gets ya from fig 1 to fig 2 (beep! paging Senor Bonferroni). I've got me a headache so I'm not gonna read it to confirm that it was ex post facto.
Obviously we don't know how well it will apply to people that aren't post-menopausal women.
This finding is more impressive considering that white women in rural Nebraska are almost certainly a fair bit more equatorially-positioned than their ancestors. Nebraska-wide ethnies, co/ the US census:
German38.6
Irish13.4
English9.6
Swedish4.9
Czech4.9
Obviously, if you got a lot of melanin and you move away from the equator, you have a bigger potential vitamin D issue, whereas the opposite is true for these Northern Europeans in Nebraska.
"This finding is more impressive considering that white women in rural Nebraska are almost certainly a fair bit more equatorially-positioned than their ancestors."
How dark were the native Americans from that region? Did they obtain a substantial amounts of vitamin d from their diets?
Hmm, I usually "imagine" all aboriginal North Americans including Inuit as being about the same tone (a little darker than Chinese) - but I really have no clue if that's right. The correlation of skin reflectivity with latitude is imperfect but very strong (see Nina Jablonski's papers).
At least in today's USA, there is a marked circannual variation in the serum level of 25-hydroxy-D, the reservoir form of the vitamin, with the nadir in winter - therefore it seems that sunlight-derived D is usually a good bit more important than dietary D. The only foods that have much of it are yolk, fatty fish, and liver. Yolk is some weak shit at 25 IU per egg, fatty fish can be a fairly potent source, and I'm not sure about liver.