Impact of physical activity levels on the association between air pollution exposures and glycemic indicators in older individuals

Abstract

BackgroundAir pollution may exacerbate diabetes-related indicators; however, the longitudinal associations between air pollutant concentrations and glycemic markers remain unclear. In this prospective cohort study, we examined the longitudinal associations between air pollution and glycemic indicators among older individuals with normoglycemia at baseline and determined whether these associations differed according to changes in physical activity levels.MethodsOverall, 1,856 participants (mean age, 70.9 years) underwent baseline and 4-year follow-up surveys. We used linear mixed-effect models to examine the associations between previous 1-year exposures to air pollutants and glycemic indicators. We further investigated associations between previous 5-year exposures to air pollutants and glycemic indicators after the inverse probability of treatment weighting (IPTW). We explored effect modifications by the level of physical activity maintenance and changes in metabolic equivalent of task (METs) for physical activity.ResultsLevels of particulate matter with aerodynamic diameters <= 10 mu m (PM10) and <= 2.5 mu m, and nitrogen dioxide (NO2) were significantly associated with increased fasting blood glucose, Hemoglobin A1c, insulin, and homeostatic model assessment for insulin resistance (HOMA-IR) values. After IPTW, the associations remained significant for PM10 and NO2. The positive associations of NO2 with insulin and HOMA-IR remained significant in the maintained inactive group, but not in the maintained moderate-to-vigorous active group. The positive associations of PM10 or NO2 with insulin and HOMA-IR remained significant in the group with increased METs, but not in those with decreased METs. In the post-hoc analysis of non-linear relationships between an increase in METs and glycemic indicators, insulin and HOMA-IR remarkably increased in the higher PM10 and NO2 exposure group from the point of 12,000 and 13,500 METs-min/week increase, respectively.ConclusionsWe demonstrated longitudinal associations between air pollution exposures and increased insulin resistance in older individuals. Maintaining moderate-to-vigorous physical activity may mitigate the adverse effects of air pollution on insulin resistance. In older individuals dwelling in highly polluted areas, an increase of less than 12,000 METs-min/week may be beneficial for insulin resistance. Why did we undertake this study?Air pollution exposures may increase the risk of diabetes mellitus; however, the impacts of changes in physical activity on the associations between air pollution exposures and glycemic indicators remained unclear.What is the specific question(s) we wanted to answer?We investigated the associations of previous 1-year and 5-year air pollution exposures with glycemic indicators in older individuals with normoglycemia and explored the potential impacts of changes in physical activity levels on the associations.What did we find?Previous 1-year exposures to PM10 and NO2 were associated with elevated fasting blood glucose, Hemoglobin A1c, insulin, and insulin resistance. Previous 5-year exposures to PM10 and NO2 were associated with increased insulin resistance. The adverse effects of NO2 existed in those who maintained inactive but not in those with maintained moderate-to-vigorous activity.What are the implications of our findings?Our findings underscore the detrimental impact of air pollution on glycemic health and emphasize that maintaining moderate to vigorous physical activity may mitigate the adverse effects of air pollution on insulin resistance in older individuals.