Infant mortality, season of birth and the health of older Puerto Rican adults

The increasing prevalence of heart disease and diabetes among aging populations in low and middle income countries leads to questions regarding the degree to which endogenous early life exposures (exposures in utero) are important determinants of these health conditions. We devised a test using infant mortality (IMR) to verify if season of birth is a good indicator of early life (in utero) conditions that precipitate adult onset of disease. We linked annual IMR at the municipality (municipio) level from the late 1920s to early 1940s with individual birth year and place using a representative sample of older Puerto Rican adults (n = 1447) from the Puerto Rican Elderly: Health Conditions (PREHCO) study. We estimated the effects of season of birth on adult heart disease and diabetes for all respondents and then for respondents according to whether they were born when IMR was lower or higher, controlling for age, gender, obesity, respondent’s educational level, adult behavior (smoking and exercise) and other early life exposures (childhood health, knee height and childhood socioeconomic status (SES)). The pattern of effects suggests that season of birth reflects endogenous causes: (1) odds of heart disease and diabetes were strong and significant for those born during the lean season in years when IMR was lower; (2) effects remained consistent even after controlling for other childhood conditions and adult behavior; but (3) no seasonality effects on adult health for adults born when IMR was higher. We conclude that in this population of older Puerto Rican adults there is continued support that the timing of adverse endogenous (in utero) conditions such as poor nutrition and infectious diseases is associated with adult heart disease and diabetes. It will be important to test the validity of these findings in other similar populations in the developing world.

► Season of birth, an indicator of early life exposures (poor nutrition and infectious diseases), was strongly associated with heart disease and diabetes among older adult Puerto Ricans (60–74 years old). Being born during the lean season greatly increased the odds of adult heart and diabetes as compared with being born during the harvest season.
► An analysis using IMR suggests that season of birth in this case reflects endogenous (in utero) conditions. Thus, there is continued support that in utero conditions are associated with older adult health.
► Under restricted conditions season of birth may help illuminate the effects of early life on older adult health.
► Replication of these findings in other similar aging populations in low and middle income countries is important.