Understanding the genetic adaptations that occurred as humans migrated out of Africa to higher latitudes helps explain on a population-wide level how UV radiation (UVR) exposure will have varying consequences and benefits in patients of different skin pigmentations. It has been hypothesized that the need for efficient vitamin D synthesis was the primary driver for the skin-lightening process that evolutionarily occurred as humans migrated to higher latitudes. This review analyzes the level of support for the hypothesis that skin lightening occurred to enable adequate vitamin D synthesis in populations that migrated to areas with less UVR. Our literature search supported the hypothesis that through natural selection and intricate genetic adaptations, humans who migrated to areas with lower levels of UVR underwent a skin-lightening process to avoid the consequences of vitamin D deficiency. Our review includes an analysis of migration patterns out of Africa and how these affected pigmentation genes that are found in certain ethnic populations can be used to better understand this critical adaptation process when counseling patients on the need for sun protection.

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Practice Points

Sufficient UV radiation exposure is required to synthesize vitamin D, but excess exposure increases skin cancer risk.
Genes associated with vitamin D production and melanin synthesis form an interconnected network that explains skin tone polymorphisms and their influence on healthy sun behaviors.
Adaptations in genetics of skin pigmentation and vitamin D metabolism due to anthropologic patterns of migration to northern latitudes may help explain predisposition to dermatologic diseases such as skin cancer.

References

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The risk for developing skin cancer can be somewhat attributed to variations in skin pigmentation. Historically, lighter skin pigmentation has been observed in populations living in higher latitudes and darker pigmentation in populations near the equator. Although skin pigmentation is a conglomeration of genetic and environmental factors, anthropologic studies have demonstrated an association of human skin lightening with historic human migratory patterns.¹ It is postulated that migration to latitudes with less UVB light penetration has resulted in a compensatory natural selection of lighter skin types. Furthermore, the driving force behind this migration-associated skin lightening has remained unclear.¹

The need for folate metabolism, vitamin D synthesis, and barrier protection, as well as cultural practices, has been postulated as driving factors for skin pigmentation variation. Synthesis of vitamin D is a UV radiation (UVR)–dependent process and has remained a prominent theoretical driver for the basis of evolutionary skin lightening. Vitamin D can be acquired both exogenously or endogenously via dietary supplementation or sunlight; however, historically it has been obtained through UVB exposure primarily. Once UVB is absorbed by the skin, it catalyzes conversion of 7-dehydrocholesterol to previtamin D₃, which is converted to vitamin D in the kidneys.^2,3 It is suggested that lighter skin tones have an advantage over darker skin tones in synthesizing vitamin D at higher latitudes where there is less UVB, thus leading to the adaptation process.1 In this systematic review, we analyzed the evolutionary vitamin D adaptation hypothesis and assessed the validity of evidence supporting this theory in the literature.

Methods

A search of PubMed, Embase, and the Cochrane Reviews database was conducted using the terms evolution, vitamin D, and skin to generate articles published from 2010 to 2022 that evaluated the influence of UVR-dependent production of vitamin D on skin pigmentation through historical migration patterns (Figure). Studies were excluded during an initial screening of abstracts followed by full-text assessment if they only had abstracts and if articles were inaccessible for review or in the form of case reports and commentaries.

Exploring Skin Pigmentation Adaptation: A Systematic Review on the Vitamin D Adaptation Hypothesis

References

Methods

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