Association between quantitative measures of skin color & plasma 25‐hydroxyvitamin D (25OHD)

Most vitamin D is obtained through UV synthesis in the skin. Dark‐skin ethnic groups have lower 25OHD concentrations than light skin groups; due to more skin melanin, which acts as a UV filter. Ethnicity is a proxy measure of skin color & within an ethnic group skin color varies greatly. It would be expected that the color of unexposed skin would be negatively associated with 25OHD. Conversely, as skin color darkens with sun exposure, a measure of tanning would be positively associated with 25OHD. Skin color can be quantified using reflectance colorimetry with higher numbers indicating darker skin. We aimed to determine the association between constitutive (upper inner‐arm) & sun‐induced (forearm) skin color & 25OHD in a group of Pacific Islanders (n=82) & Europeans (n=239) living in NZ (47°S) in summer. Mean (SD) serum 25OHD was 88 (31) nmol/L for Europeans and 75 (34) nmol/L for Pacific Islanders. Based on constitutive skin color measurements 36% of participants were very light, 45% light, 15% intermediate, 4% tanned, & 1% dark. Tanning at the forearm but not constitutive skin color was a significant predictor of 25OH D. Each 10 unit higher value at the forearm (less tanning) was associated with a ~4.9 nmol/L lower 25OHD (P<0.001). Tanning was a more important predictor of 25OHD than constitutive skin color in this population. Further study is needed in a population with a wider range of constitutive skin color.