For those worried by being in the higher 'normal' as currently defined vitamin D ranges, this is a fascinating paper looking at vitamin D levels in 'non westernised' Peoples in central Africa.
It is important to keep in mind that light skinned people can make more vitamin D per unit of UVB than dark skinned people.
Very dark skins have a similar blocking effect on UVB to factor 15 sunscreen.
Paleolithic Caucasians living in more northerly latitudes would only have been able to make vitamin D in the summer months, and would have had to store vitamin D for the winter, which may account for the higher levels seen in beach guards . . .
Do Caucasians have a higher vitamin D need; we do not know, but the figures below clearly show that Peoples with dark skins given sufficient exposure to sunlight containing UVB will make significant amounts of vitamin D, with an 'average' 115nmol/l which is well above the start point of current official medical recommendations (30ng =75nmol/l) of what is considered 'optimal' .
It is interesting and raises fascinating questions that pregnant women had higher vitamin D levels, which were around 140nmol/l; in comparison a recent study http://www.pediatricsdigest.mobi/con....full.pdf+html of vitamin D levels in pregnant women demonstrating a significant effect for vitamin D on development of verbal skills in infants records that the level in quartile 1 were average 36.81, and in the highest in quartile 4 83.4nmol/l, which are way below 140nmol/.
Vitamin D status indicators in indigenous populations in East Africa
http://link.springer.com/article/10....394-012-0421-6
Martine F. Luxwolda,
Remko S. Kuipers,
Ido P. Kema,
E. van der Veer,
D. A. Janneke Dijck-Brouwer,
Frits A. J. Muskiet
Abstract
Purpose
Sufficient vitamin D status may be defined as the evolutionary established circulating 25-hydroxyvitamin D [25(OH)D] matching our Paleolithic genome.
Methods
We studied serum 25(OH)D [defined as 25(OH)D2 + 25(OH)D3] and its determinants in 5 East African ethnical groups across the life cycle: Maasai (MA) and Hadzabe (HA) with traditional life styles and low fish intakes, and people from Same (SA; intermediate fish), Sengerema (SE; high fish), and Ukerewe (UK; high fish). Samples derived from non-pregnant adults (MA, HA, SE), pregnant women (MA, SA, SE), mother–infant couples at delivery (UK), infants at delivery and their lactating mothers at 3 days (MA, SA, SE), and lactating mothers at 3 months postpartum (SA, SE). Erythrocyte docosahexaenoic acid (RBC-DHA) was determined as a proxy for fish intake.
Results
The mean ± SD 25(OH)D of non-pregnant adults and cord serum were 106.8 ± 28.4 and 79.9 ± 26.4 nmol/L, respectively. Pregnancy, delivery, ethnicity (which we used as a proxy for sunlight exposure), RBC-DHA, and age were the determinants of 25(OH)D. 25(OH)D increased slightly with age. RBC-DHA was positively related to 25(OH)D, notably 25(OH)D2. Pregnant MA (147.7 vs. 118.3) and SE (141.9 vs. 89.0) had higher 25(OH)D than non-pregnant counterparts (MA, SE). Infant 25(OH)D at delivery in Ukerewe was about 65 % of maternal 25(OH)D.
Conclusions
Our ancient 25(OH)D amounted to about 115 nmol/L and sunlight exposure, rather than fish intake, was the principal determinant. The fetoplacental unit was exposed to high 25(OH)D, possibly by maternal vitamin D mobilization from adipose tissue, reduced insulin sensitivity, trapping by vitamin D-binding protein, diminished deactivation, or some combination.