Lifespan depends on month of birth

Month of birth influences adult life expectancy at ages 50+. Why? In two co untries of the Northern Hemisphere-Austria and Denmark-people born in autum n (October-December) live longer than those born in spring (April-June). Da ta for Australia show that, in the Southern Hemisphere, the pattern is shif ted by half a year. The lifespan pattern of British immigrants to Australia is similar to that of Austrians and Danes and significantly different from that of Australians. These findings are based on population data with more than a million observations and little or no selectivity. The differences in lifespan are independent of the seasonal distribution of deaths and the social differences in the seasonal distribution of births. In the Northern Hemisphere, the excess mortality in the first year of life of infants born in spring does not support the explanation of selective infant survival. In stead, remaining life expectancy at age 50 appears to depend on factors tha t arise in utero or early in infancy and that increase susceptibility to di seases later in life. This result is consistent with the finding that, at t he turn of the last century, infants born in autumn had higher birth weight s than those born in other seasons. Furthermore, differences in adult lifes pan by month of birth decrease over time and are significantly smaller in m ore recent cohorts, which benefited from substantial improvements in matern al and infant health.