Syst Rev. 2026 Mar 4. doi: 10.1186/s13643-026-03108-x. Online ahead of print.
ABSTRACT
BACKGROUND: Chronic diseases (cardiovascular, cancer, respiratory, diabetes and chronic kidney disease) account for over 80% of global mortality and remain a leading public health challenge. Although water intake is essential to physiological function and homeostasis, its role in the long-term prevention of chronic diseases remains underexplored. Current guidelines are vague, inconsistent, and aimed at preventing acute dehydration, without robust evidence supporting benefits for chronic disease prevention. This study outlines a preliminary systematic review designed to synthesise existing literature on plain water intake and chronic disease risk, with the aim of laying the groundwork for future public health recommendations.
METHODS: This review will include English-language randomised controlled trials, cross-sectional studies, case-control studies, and cohort studies assessing the relationship between plain water intake and the incidence of chronic diseases in healthy adults. Only studies measuring oral plain water consumption will be included. Adequate water intake is defined as 2 to 3.7 l daily, based on current international and national recommendations. Eligible studies must report on the risk of developing one or more major chronic diseases and provide quantifiable outcomes (e.g. odds ratios, or relative risks with 95% confidence intervals). A meta-analysis will be conducted where appropriate, and subgroup and sensitivity analyses will explore potential sources of heterogeneity.
DISCUSSION: This systematic review is the first to collate evidence on the collective relationship between plain water intake and multiple chronic disease outcomes. By adopting a binary classification (adequate versus inadequate intake), this preliminary synthesis aims to generate practical and actionable insights that are accessible to the general public. Recognising the fragmented nature of existing research, the findings will serve as a foundation for future studies to refine thresholds and inform clinical and public health guidelines. Limitations such as self-reported data, residual confounding, exclusion of non-English studies, and variability in intake measurement, will be transparently addressed in the interpretations of results.
SYSTEMATIC REVIEW REGISTRATION: PROSPERO; CRD420251021321. It can be accessed from https://www.crd.york.ac.uk/PROSPERO/view/CRD420251021321.
PMID:41776702 | DOI:10.1186/s13643-026-03108-x