Associations between short-term exposure to ambient temperature and renal disease mortality in Japan during 1979-2019: A time-stratified case-crossover analysis.

Background: Previous studies have indicated that renal disease mortality is sensitive to ambient temperatures. However, most have been limited to the summer season with inconclusive evidence for changes in population vulnerability over time. Objective: This study aims to examine the association between short-term exposure to ambient temperatures and mortality due to renal diseases in Japan, and how this association varied over time. Methods: We conducted a two-stage, time-stratified case-crossover study from 1979 to 2019 across 47 prefectures of Japan. We obtained the data of daily mortality counts for all renal diseases, acute renal failure, and chronic renal disease. We fitted a conditional quasi-Poisson regression model with a distributed lag nonlinear model. A random-effects meta-analysis was applied to calculate national averages. We performed additional analyses by four subperiods, sex, and age groups. Results: We analyzed 997,590 renal mortality cases and observed a reversed J-shaped association. Lower temperatures were associated with increased mortality in all renal disease categories. The cumulative relative risks at 2.5th percentile compared to the minimum mortality temperature percentile were 1.34 (95% confidence interval [CI] = 1.29, 1.40), 1.51 (95% CI = 1.33, 1.71), and 1.33 (95% CI = 1.24, 1.43) for all renal, acute renal failure, and chronic renal disease mortality, respectively. The associations were observed in individuals of both sexes and aged 65 years and above. The associations of kidney mortality with low temperature remained consistent, while the associations with high temperature were pronounced in the past, but not in recent periods. Conclusions: Protection for individuals with impaired renal function from exposure to low temperatures during cold seasons is warranted.