Long-term exposure to specific humidity and cardiovascular disease hospitalizations in the US Medicare population

Abstract

BACKGROUND AND AIM: Most studies that evaluate associations of weather on human health focus on temperature. Less is known about health effects of humidity. We evaluated associations of long-term exposure to specific humidity with cardiovascular disease (CVD), coronary heart disease (CHD) and cerebrovascular disease (CBV) hospitalization. METHODS: We constructed an open cohort consisting of all fee-for-service Medicare beneficiaries, aged ≥65, living in the contiguous US from 2000 through 2016 (~63 million individuals). We assessed zip code level annual (January-December), summer (June-August) and winter (December-February) average specific humidity and specific humidity variability (standard deviation) for each year, based on daily specific humidity estimates from the Gridded Surface Meteorological dataset (~4km spatial resolution). To estimate associations of specific humidity with first CVD, CHD and CBV hospitalization, we used Cox-equivalent Poisson models. RESULTS:After adjustment for individual and area-level indicators and temperature, higher annual and summer average specific humidity and lower winter average specific humidity were associated with an increased risk of CVD, CHD and CBV hospitalization. For summer average specific humidity, we found HRs of 1.07 (95%CI: 1.07, 1.08) for CVD hospitalization, 1.08 (95%CI: 1.08, 1.09) for CHD hospitalization and 1.07 (95%CI: 1.07, 1.08) for CBV hospitalization per IQR increase (4.0 g of water vapor/kg of dry air). Higher annual, summer and winter specific humidity variability were also associated with increased risk of CVD, CHD and CBV hospitalization. Associations of annual and summer average specific humidity were strongest for beneficiaries eligible for Medicaid and for beneficiaries with an unknown or other race. CONCLUSIONS:Among this cohort of US Medicare beneficiaries, higher annual and summer average specific humidity and higher annual, summer and winter specific humidity variability were positively associated with CVD, CHD, and CBV hospitalization. Associations were modified by race and Medicaid eligibility. KEYWORDS: humidity, cardiovascular diseases, climate