Seasonal average temperature differences and CVD incidence: results from the US-based Nurses' Health study, Nurses' Health Study II, and the Health Professional Follow-up study.

Background: Climate change is one of the greatest health threats facing humanity. Multiple studies have documented the impact of short-term temperature exposure on human health. However, long-term temperature exposures are far less studied.

Objectives: We examined whether exposure to higher or lower summer and winter average temperatures compared to long-term average temperatures were associated with cardiovascular disease (CVD) incidence in three US-based cohorts.

Methods: We followed 276,618 participants from the Nurses' Health Study (NHS, 1991-2018), the NHSII (1994-2017), and the Health Professionals' Follow-Up Study (1991-2015). We used data (1986-2018) from PRISM Spatial Climate Datasets (800 × 800m spatial resolution) to calculate differences between the summer (June-August) and winter (December-February) average temperatures and the previous 5-year summer and winter average temperatures at residential addresses of each participant. CVD incidence was defined as first nonfatal or fatal MI or nonfatal or fatal stroke. Cox proportional hazard models were used to examine associations with between average temperatures and CVD incidence. Hazard ratios (HRs) and 95% confidence intervals (95%CI) were pooled using random effect meta-analysis. We also examined associations in the populations aged <65 and 65+ years.

Results: After pooling HRs, we found no association of summer average temperatures higher than the previous 5-year average temperature, with CVD incidence. A winter average temperature lower than the previous 5-year average was associated with CVD incidence (HR = 0.96 per 2.7°C increase, 95%CI: 0.94, 0.98). Among persons aged <65 years, we observed increased CVD risks with higher summer average temperatures (pooled HR = 1.03 per 1.3°C increase, 95%CI: 1.00, 1.07) and lower winter average temperatures (pooled HR = 0.91 per 2.7°C increase, 95%CI: 0.87, 0.94) compared to the previous 5-year average temperature.

Discussion: Exposure to a winter average temperature lower than the previous 5-year average was associated with an increased CVD risk. Exposure to a summer average temperature higher than the previous 5-year average was associated with CVD incidence in the population aged <65 years, but not in the full population. https://doi.org/10.1289/EHP14677.