Historical Migration and Contemporary Health

We show that migration during the last 500 years induced differences in contemporary health outcomes. Our theory is related to the risks of premature death, and builds on three physiological facts. First, vitamin D... [ view full abstract ]

We show that migration during the last 500 years induced differences in contemporary health outcomes. Our theory is related to the risks of premature death, and builds on three physiological facts. First, vitamin D deficiency is directly associated with higher risk of all-cause mortality. Second, the ability of humans to synthesize vitamin D from sunlight (i.e., ultraviolet radiation, UV-R) declines with skin pigmentation. Third, skin pigmentation is the result of an evolutionary compromise between its costs (higher risk of vitamin D deficiency) and its benefits (lower risk of skin cancer), which explains why natives of high UV-R regions became more intensely pigmented. In accord with these physiological premises, when individuals indigenous to high UV-R regions migrate to low UV-R regions, the risk of vitamin D deficiency rises markedly, and with it the risk of premature death. We develop a measure that allows us to explore the aggregate health consequences of migration, as caused by the potential risk of vitamin D deficiency induced by historical population flows. Our results show that the potential risk of vitamin D deficiency induced by migration between 1500 and 2000 holds strong explanatory power vis-à-vis aggregate indicators of health today, across countries, and across US states.