Seasonal variation in hydration status among community‐dwelling elderly in Japan

Aim While the heat during the summer season may dehydrate the elderly, little is known about the seasonal variation in dehydration. This study aimed to investigate the seasonal variation in hydration status among the community‐dwelling elderly in Japan. Methods We retrospectively analyzed the data collected after an overnight fast of adults aged ≥65 years who had no advanced kidney disease and underwent an annual health checkup at Nihon University Hospital between January and December 2019. Participants were classified according to their checkup date, whether summer (n = 265) or not summer (n = 638). The not summer group was subdivided into spring (n = 235), autumn (n = 213) and winter (n = 190). Results Among the four seasons, the spring group showed the highest levels of plasma osmolality (306.1 ± 3.9 mOsm/L), urine specific gravity (1.0172 ± 0.0058) and prevalence rates of urine specific gravity ≥1.020 (34.0%). However, seasonal differences were clinically mild, and >90% of participants showed plasma osmolality ≥300 mOsm/L, indicating dehydration, in all four seasons. The summer group showed lower urine specific gravity levels (1.0150 ± 0.0062 vs. 1.0165 ± 0.0064, P