Early Life Health and Cognitive Function in Old Age.

Abstract

Child health in the United States improved dramatically over the twentieth century. Data from the National Center for Health Statistics indicate the infant mortality rate was 23 times greater in 1900 than in 2004. The mortality rate of one-to four-year-old children, although lower in absolute terms, had a larger proportionate decline: the value in 1900 was 66 times that in 2004. The proximate cause of the mortality decline was a reduction in infectious disease. Between 1900 and 1998, the percentage of deaths of children age 1 to 19 due to infectious disease is estimated to have declined from 61.6 percent to 2 percent (Bernard Guyer et al. 2000). Major causes of child death included diarrhea, pneumonia and other respiratory infections, diphtheria, typhoid, measles, scarlet fever, whooping cough, and tuberculosis (Guyer et al. 2000). The mortality decline was accompanied by reductions in morbidity among surviving children. There were also declines in the prevalence of a host of illnesses, such as hookworm and trachoma, which were not deadly but which impaired children’s quality of life (C. Hoyt Bleakley 2007; Shannen K. Allen and Richard D. Semba 2002). Early life exposures to infectious disease may also have adverse effects on health and well-being into old age. If true, then the benefits of the twentieth century decline in infectious disease in the United States are still being realized. We examine whether the disease environments experienced by American children in the first half of the twentieth century are associated with their cognitive abilities at older ages. We match region-level historical data on mortality from a variety of infectious diseases, as well as total infant mortality, with information on the cognitive function of older Americans followed by the Health and Retirement Study (HRS). We find evidence that the burden of disease in early life—measured using either mortality rates by cause or the overall infant mortality rate—is significantly associated with performance on cognitive tests in old age.