Increased skin pigment reduces the capacity of skin to synthesise vitamin D3.
Level 4 - case-series / case-control
Very small non-randomized volunteer experimental study (case series design).
PubMed 6119494 · doi:10.1016/s0140-6736(82)90214-8
What was done
Circulating vitamin D concentrations were measured in two lightly pigmented Caucasian and three heavily pigmented Black volunteers following whole-body exposure to a single standard dose of ultraviolet radiation (UVR; 1 minimal erythemal dose). One Black volunteer was subsequently re-exposed to a UVR dose six times larger than the standard dose to assess dose responsiveness.
What was found
In Caucasian subjects, 1 minimal erythemal dose of UVR increased serum vitamin D concentrations by up to 60-fold at 24 to 48 hours post-exposure. In Black subjects, the standard dose produced no significant change in circulating vitamin D. Re-exposure of one Black subject to six times the standard UVR dose produced serum vitamin D concentrations comparable to those observed in Caucasian subjects at the lower dose.
Why it matters
This seminal study provided early physiological evidence that cutaneous melanin acts as a natural optical filter, substantially increasing the threshold of UV radiation needed to trigger cutaneous vitamin D3 synthesis.
Limits
The study evaluated an extremely small sample size (n=5 total; 2 Caucasian and 3 Black participants), and high-dose re-testing was performed in only a single individual. Detailed demographic variables, baseline nutritional status, and precise baseline vitamin D metabolite concentrations were not reported in the abstract.
Cited by
- context A University of Chicago study found that African-Americans in Chicago need to spend six times as long in the sun as Caucasians to synthesize the same amount of vitamin D.