Effects of plain water intake before bedtime on sleep and depressive mood among middle-aged Japanese men

Sep 29, 2026

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Adequate water intake during the day supports mental health, but its role during sleep is unclear. The study examined how drinking plain water before bedtime affects sleep parameters and depressive mood among middle-aged Japanese men. A survey of 2,000 participants assessed associations using CES-D (Study 1), and a controlled comparison tested 280 mL of plain water versus no beverages for at least 2 hours (Study 2). Plain water reduced morning depressive mood, affected REM sleep, and increased nocturia likelihood.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages15

Reading Time38 min

AccessFree to download

Abstract

Introduction

Water and hydration physiology

Dehydration and depressive mood

Study rationale and objectives

OPEN ACCESS Citation: Kaida K, Itoi K, Soeta Y, Ooie T, Oishi K (2026) Effects of plain water intake before bedtime on sleep and depressive mood among middle-aged Japanese men. PLoS One 21(1): e0340490. [https://doi.org/10.1371/](https://doi.org/10.1371/)[ ](https://doi.org/10.1371/)[journal.pone.0340490](journal.pone.0340490) Editor: Yosuke Yamada, National Institute of Biomedical Innovation Health and Nutrition, JAPAN Received: May 19, 2025 Accepted: December 21, 2025 Published: January 6, 2026 Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: [https://doi.org/10.1371/journal](https://doi.org/10.1371/journal). pone.0340490 Copyright: © 2026 Kaida et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, RESEARCH ARTICLE Effects of plain water intake before bedtime on sleep and depressive mood among middle-aged Japanese men Kosuke Kaida1*, Kazane Itoi1, Yoshiharu Soeta2, Toshihiko Ooie3,4, Katsutaka Oishi3,5,6 1 Institute for Information Technology and Human Factors, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan, 2 Molecular Biosystems Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka, Japan, 3 Cellular and Molecular Biotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan, 4 Medilux Research Center, Nara Institute of Science and Technology (NAIST), Ikoma, Nara, Japan, 5 Department of Applied Biological Science, Graduate School of Science and Technology, Tokyo University of Science, Noda, Chiba, Japan, 6 Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba, Japan * [kaida.kosuke@aist.go.jp](kaida.kosuke@aist.go.jp) Abstract Although adequate water intake during the day enhances mental health, its effects during sleep remain unknown. We aimed to define the impact of plain water intake before bedtime on sleep parameters and depressive mood. We surveyed 2,000 Japanese using a questionnaire to determine associations between pre-bedtime water intake and depressive mood measured using the Center for Epidemiologic Studies Depression Scale (CES-D; Study 1) . We also compared the effects of consuming 280 mL of plain water immediately before bedtime and of not consuming any beverages for at least 2 hours before bedtime (Study 2) . The findings of Study 2 indicated that plain water intake immediately before bedtime decreased depressive mood in the morning, prolonged REM sleep latency, and reduced the duration of REM sleep. However, plain water intake also increased the likelihood of nocturia. Although balancing advantages and disadvantages is essential, the practice of consuming plain water before bedtime is a simple and effective way to enhance subjective wellbeing. Introduction Water accounts for 50%–70% of human body weight [ 1] . Water is crucial for survival and a critical physiological issue in terms of hypohydration, or dehydration [2] . The physiological water content is associated with blood pressure regulation [3] and all animals require water to rehydrate and alleviate thirst [4] . Adult humans should drink at least 2 L of plain water daily to prevent dehydration and maintain hydration. Water constantly evaporates from the surface of the body not only while awake, but also during sleep [5] . This means that 400–700 mL of water evaporate from PLOS One | [https://doi.org/10.1371/journal.pone.0340490](https://doi.org/10.1371/journal.pone.0340490) January 6, 2026 1 / 15 and reproduction in any medium, provid

FAQs

What was the main aim of the study?

To determine the impact of plain water intake before bedtime on sleep parameters and depressive mood among middle-aged Japanese men.

How were participants assessed for depressive mood and its relationship to water intake?

Depressive mood was measured using the Center for Epidemiologic Studies Depression Scale (CES-D) based on a questionnaire survey of 2,000 Japanese participants (Study 1).

What were the key findings regarding sleep and depressive mood after drinking water before bed?

Consuming plain water immediately before bedtime decreased depressive mood in the morning, prolonged REM sleep latency, and reduced REM sleep duration, while also increasing the likelihood of nocturia (Study 2).

Sep 29, 2026

Uploaded by OmBimo