During the past 30 years, a mortality gap developed between Lolland-Falster (the rural-provincial southeastern part) and the rest of Denmark. A main driver was selective in-migration of Danes with a high risk of death, especially of working-ages. In the present study, we determined the role of economic status in this selective in-migration. We used individual-level data from the Central Population Register and data on income source; self- or publicly supported. The study population included people aged 30-64 and living in Denmark at any time between 1992 and 2018. Mortality rate ratios (MRR) were calculated using Poisson regression for three time-periods: 1992-1999, 2000-2009 and 2010-2018. Two in five in-migrants to Lolland-Falster were people on public support. In 2010-2018, they had an MRR of 8.71 (95% confidence interval (CI): 8.05-9.42) compared with self-supported people, and an MRR of 1.49 (95% CI: 1.38-1.61) compared with publicly supported people elsewhere in Denmark. In-migration of working-aged people on public support was a main contributor to the excess mortality in Lolland-Falster as compared with the rest of Denmark. To understand urban-rural differences in health, population movements and national income patterns are important to take into account.
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