Further Evidence: Sunlight Alone is Insufficient to Rise Vitamin D Levels in Non-Western Immigrants

Wicherts et.al. (Wicherts. 2010) published the results of an investigation into the effectiveness of a) sun exposure or b) supplementation with daily 800 IU or 100,000 IU once in three months on serum 25(OH)-D3 levels in 211 otherwise healthy non-western immigrant in the Netherlands.  As you can see in table 1, the initial high dose of 100.000 IU raised 25(OH)D levels significantly faster but to a lower extent than the 800 IU daily dosing:

Table 1: Proportion (%) of participants with serum 25(OH)D<25, 25−50, 50−75, or >75 nmol/l at baseline, 3, 6, and 12 months according to treatment group 800 IU/day, 100,000 IU/3 months or sunshine exposure (Wicherts. 2010. Table 2)

Otherwise, Wickerts' study confirms the results of earlier investigations,

mean serum 25(OH)D increased to 53 nmol/l with 800 IU/day, to 50.5 nmol/l with 100,000 IU/3 months, and to 29.1 nmol/l with advised sunlight exposure.

Though, even according to the "old" reference ranges, a 25(OH)D level <30 nmol/l does not ascertains a sufficient supply with a vitamin the importance of which scientists come to realize only in the last couple of years. Wicherts would thus not only have to conclude that

[...] Vitamin D supplementation is more effective than advised sunlight exposure for treating vitamin D deficiency in non-western immigrants,

but also, that vitamin D supplementation is indicated in non-western (dark skinned) immigrants to the northern hemisphere, where sun exposure is limited and insufficient to provide them with sufficient amounts of vitamin D.