Abstract
The escalating effects of climate change, particularly global warming, are posing an increasing burden on human health. Older adults are particularly susceptible to the impact of extreme heat. Adequate water intake is essential to prevent dehydration in hot environments. Therefore, it is important to understand water turnover (WT) and intake. WT of older adults in hot environments remains unknown. This study aimed at investigating the seasonal effects on WT, total energy expenditure (TEE), and physical activity using doubly labeled water (DLW) and a triaxial accelerometer. A total of 26 older Japanese adult males and females aged ≥ 65 years participated in the study. WT and TEE were measured using DLW in May and August 2012. The mean values of maximum, mean, and minimum temperatures and mean humidity of the measurement days were 24 °C, 19 °C, 14 °C, and 57% in May (spring) and 35 °C, 29 °C, 25 °C, and 66% in August (summer) 2012, respectively. The mean (standard deviation, SD) age of the participants was 73.7 (5.4) years. Total body water increased significantly from 31.1 (4.6) to 31.9 (5.2) kg (+ 0.8 kg, P = 0.009) from May to August. TEE decreased significantly from 2271 (280) to 2123 (470) kcal/day (- 149 kcal/d, P = 0.036), while WT increased significantly from 2.939 (0.625) to 3.579 (0.943) L/day (+ 0.640 L/d, P < 0.001). WT increased by 640 mL/day during summer compared to that during spring, when the average temperature was 19 °C. Our findings indicate that WT increases during hot weather in older adults, reflecting seasonal adaptation.
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The original contributions of this study are included in this article. Further inquiries can be directed to the corresponding author, Yosuke Yamada.
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Acknowledgements
The authors would like to express our gratitude to all individuals who participated in the Kyoto–Kameoka Study as examiners for their valuable contributions to this work. We also acknowledge the administrative staff of Kameoka City and Kyoto Prefecture for their support. Finally, we express our sincere gratitude to all participants for their cooperation in this study. We would like to thank all investigators and volunteers who participated in this study, as well as Editage (www.Editage.jp) for English language editing.
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This work was supported by the Japan Society for the Promotion of Science (KAKENHI grant numbers 24240091 to K.M. and 15H05363, 24H00683 to Y.Y.) and Suntory Holdings Limited, Osaka, Japan. The funding source had no role in the study design, data collection, analysis, interpretation, article writing, or decision to submit the article for publication.
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The authors’ responsibilities are as follows: Y.Y., H.-K.K., and M.K.: conceptualization; Y.Y., T.Y., E.Y., H.N., and H.-K.K.: data curation; H.-K.K., A.I., and Y.Y.: formal analysis; Y.Y., T.Y., Yui.N., K.Y., H.S., and M.K.: investigation; Y.Y., H.-K.K., T.Y., Y.W., R.O., and M.K.: methodology; Y.Y. and M.K.: project administration; Y.Y., R.T., Y.N., N.T., and M.K.: resources; Y.Y. and M.K.: supervision; H.-K.K.: visualization; H.-K.K. Yui.N., and Y.Y.: writing—original All the authors have read and approved the final manuscript.
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R.T., Y.N., and N.T. are employees of Suntory Holdings Limited. Y.Y. received a research grant from Suntory Holdings Ltd. The other authors declare no competing interests.
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Kim, HK., Nakayama, Y., Yoshida, T. et al. Hydration, water requirements, and energy balance from spring to summer in free-living older adults: a doubly labelled water study. Sci Rep (2026). https://doi.org/10.1038/s41598-026-38832-w
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DOI: https://doi.org/10.1038/s41598-026-38832-w
