1Anthropology, The Pennsylvania State University, 2Research, Stellenbosch Institute for Advanced Study, 3Institute of Infectious Disease and Molecular Medicine, University of Cape Town, 4Centre for Evidence-based Health Care, Stellenbosch Institute for Advanced Study
April 21, 2017 , Studio 7
In this study, we investigated the relationship between skin pigmentation, UVB exposure, and cutaneous vitamin D production in healthy young adults under non-laboratory conditions. We chose to study people in the Western Cape province of South Africa because the region has a seasonal pattern of UVB exposure and because it has a heterogeneous population, which reflects centuries of migration and genetic admixture. We selected 50 healthy young adults from neighboring populations of the Cape Flats near Cape Town, designated the Xhosa and Cape Mixed cohorts. Physical examination, skin reflectance measurements, administration of dietary and sun exposure surveys, and phlebotomy were conducted on both cohorts in late January/early February 2013 (after the solar UVB maximum) and in late July/early August 2013 (after the solar UVB minimum). As described elsewhere (Coussens, A.K. et al., 2015, PNAS 112: 8052–8057), both populations exhibited seasonal fluctuations in vitamin D levels and high prevalence of winter vitamin D deficiency. By exploring within- and between-population variation in skin reflectance and pigmentation genes in the current study, we sought to better understand the relationships between pigmentation genotype and phenotype (including tanning potential), and between genes affecting skin pigmentation and vitamin D metabolism. Extensive overlap in the ranges of skin reflectance measurements between the two populations was discovered, with the Xhosa cohort being darker and exhibiting lower variance in measurements than the Cape Mixed cohort. This pattern was mirrored in pigmentation SNPs, which reflected the predicted higher level of genetic admixture in the Cape Mixed cohort.
This research was supported by funds from the Guggenheim Foundation, Stellenbosch Institute for Advanced Study, the Academy of Science (South Africa), the UK Medical Research Council, and the Wellcome Trust.