Quantifying individual and city level modification of the health effects of air pollution in older adults

Although the health risks of ambient air pollution have been well quantified in the United States, we do not yet have sufficient understanding of the underlying mechanisms. Effect modifying factors may provide insight, so we address three related issues. We develop and implement a two-step method to identify modifiers of the acute association between ambient air pollution and daily mortality counts in a subset of U.S. cities. We find amplified particulate matter effects in cities with a larger proportion of the population over the age of 65. To study the potential surrogacy of older age for health status, we investigate whether gerontologic frailty (a measure of health status in older adults) modifies the health effects of ambient air pollution. Low physical activity, a key component of a widely applied frailty definition, is assessed using a lengthy questionnaire and is frequently administratively missing. We develop and apply methods to identify and evaluate surrogate definitions of low physical activity that satisfy the dual goals of streamlining screening and filling in missing information. Using a frailty surrogate, we develop and apply models that relate individual level ambient air pollution exposure history and frailty status history to repeated measurements of lung function. We find that older adults who have spent a greater number of years being frail are more susceptible to the negative effects of cumulative pollution exposure on forced vital capacity.