Examining Skin Color and Discrimination Among Ethnic Minority Adolescents

Skin color is one of the most conspicuous ways in which humans vary and has been widely used to define human races. Here we present new evidence indicating that variations in skin color are adaptive, and are related to the regulation of ultraviolet (UV) radiation penetration in the integument and its direct and indirect effects on fitness. Using remotely sensed data on UV radiation levels, hypotheses concerning the distribution of the skin colors of indigenous peoples relative to UV levels were tested quantitatively in this study for the first time. The major results of this study are: (1) skin reflectance is strongly correlated with absolute latitude and UV radiation levels. The highest correlation between skin reflectance and UV levels was observed at 545 nm, near the absorption maximum for oxyhemoglobin, suggesting that the main role of melanin pigmentation in humans is regulation of the effects of UV radiation on the contents of cutaneous blood vessels located in the dermis. (2) Predicted skin reflectances deviated little from observed values. (3) In all populations for which skin reflectance data were available for males and females, females were found to be lighter skinned than males. (4) The clinal gradation of skin coloration observed among indigenous peoples is correlated with UV radiation levels and represents a compromise solution to the conflicting physiological requirements of photoprotection and vitamin D synthesis. The earliest members of the hominid lineage probably had a mostly unpigmented or lightly pigmented integument covered with dark black hair, similar to that of the modern chimpanzee. The evolution of a naked, darkly pigmented integument occurred early in the evolution of the genus Homo. A dark epidermis protected sweat glands from UV-induced injury, thus insuring the integrity of somatic thermoregulation. Of greater significance to individual reproductive success was that highly melanized skin protected against UV-induced photolysis of folate (Branda & Eaton, 1978, Science201, 625-626; Jablonski, 1992, Proc. Australas. Soc. Hum. Biol.5, 455-462, 1999, Med. Hypotheses52, 581-582), a metabolite essential for normal development of the embryonic neural tube (Bower & Stanley, 1989, The Medical Journal of Australia150, 613-619; Medical Research Council Vitamin Research Group, 1991, The Lancet338, 31-37) and spermatogenesis (Cosentino et al., 1990, Proc. Natn. Acad. Sci. U.S.A.87, 1431-1435; Mathur et al., 1977, Fertility Sterility28, 1356-1360).As hominids migrated outside of the tropics, varying degrees of depigmentation evolved in order to permit UVB-induced synthesis of previtamin D(3). The lighter color of female skin may be required to permit synthesis of the relatively higher amounts of vitamin D(3)necessary during pregnancy and lactation. Skin coloration in humans is adaptive and labile. Skin pigmentation levels have changed more than once in human evolution. Because of this, skin coloration is of no value in determining phylogenetic relationships among modern human groups. Copyright 2000 Academic Press.

This study investigates the association between self-reported physical and mental health and both perceived racial discrimination and skin color in African American men and women. We used data from the longitudinal coronary artery risk development in young adults study (CARDIA) in African American men and women (n=1722) in the USA. We assessed self-reported mental and physical health status and depressive symptoms at the Year 15 (2000-2001) follow-up examination using the Medical Outcomes Study Short Form (SF-12) and the Center for Epidemiologic Studies Depression scale. Skin color was measured at the Year 7 examination (1992-1993). To assess racial discrimination, we used a summary score (range 0-21) for 7 questions on experiencing racial discrimination: at school, getting a job, getting housing, at work, at home, getting medical care, on the street or in a public setting. Self-reported racial discrimination was more common in men than in women (78.1% versus 73.0%, p<0.05) and in those with higher educational attainment, independent of gender. Discrimination was statistically significantly associated with worse physical and mental health in both men and women, before and after adjustment for age, education, income, and skin color. For example, mental health (0-100 scale) decreased an average of 0.29 units per unit increase in racial discrimination score in men; this became 0.32 units after adjustment. There was no association between self-reported physical and mental health and skin color. Further studies of the health consequences of discrimination will require investigation of both the upstream determinants of discrimination and the downstream mechanisms by which perceived discrimination affects health outcomes.