Migration during the last 500 years induced differences in contemporary health outcomes: Due to vitamin D deficiency, migration from high UV radiation places to low radiation ones takes a toll on health

Historical migration and contemporary health. Thomas Barnebeck Andersen, Carl-Johan Dalgaard, Christian Volmer Skovsgaard, Pablo Selaya. Oxford Economic Papers, Volume 73, Issue 3, July 2021, Pages 955–981, https://doi.org/10.1093/oep/gpaa047

Abstract: We argue that migration during the last 500 years induced differences in contemporary health outcomes. The theory behind our analysis 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 (UV-R) declines with skin pigmentation. Third, skin pigmentation is the result of an evolutionary compromise between higher risk of vitamin D deficiency and lower risk of skin cancer. When individuals from high UV-R regions migrate to low UV-R regions, the risk of vitamin D deficiency rises markedly. We develop a measure that allows us to empirically explore the aggregate health consequences of such migration in a long historical perspective. We find that the potential risk of vitamin D deficiency induced by migration during the last half millennium is a robust predictor of present-day aggregate health indicators.

JEL I1 - HealthJ1 - Demographic EconomicsJ15 - Economics of Minorities, Races, Indigenous Peoples, and Immigrants; Non-labor Discrimination

5. Conclusion

We have examined whether a migration-induced imbalance between the intensity of skin pigmentation and ambient UV-R holds explanatory power vis-à-vis present-day global health differences. We find that it does. Consequently, our results suggest that low UV-R regions that have received substantial immigration from high UV-R regions experience lower life expectancy than would have been the case in the absence of such migration flows.

The underlying theory derives from the life sciences. Conditional on ambient UV-R, individuals with intense skin pigmentation (deriving from high ancestral UV-R exposure) are more susceptible to vitamin D deficiency, which is a leading cause of a range of afflictions that cause premature death. The contribution of the present study lies in exploring whether this theory holds explanatory power in the aggregate. The weight of the evidence presented above suggests it does.

Although the economic significance of our measure of the risk of vitamin D deficiency (if taken at face value) is relatively strong, it is also clear that its ability to account for cross-country variation in life expectancy is modest. However, if current movements of people continue, which to a large extent represent movements from ‘South to North’, much more variation is likely to become visible during the 21st century. As such, vitamin D deficiency may become an increasing public health issue in the years to come, at least in the absence of preventive public health measures.

We believe the present study could be usefully extended in the direction of studying within country migration. For example, Black et al. (2015) find that the Great Migration within the USA reduced the health of African Americans significantly. While the authors suggest that some of the impact may be linked to changes in the intake of alcohol and cigarette smoking, it is worth noting that migrants also experienced changes in the environment. For example, moving from Georgia to New York would imply a reduction in ambient UV-R of roughly 43%, implying in turn a considerable increase in the risk of vitamin D deficiency for an African American. Whether a vitamin D mechanism could be contributing to the decline in health outcomes in the aftermath of the Great Migration seems to be an interesting topic for future research.