Association between calcium intake and sleep quality: a systematic review.

Background: As the prevalence of sleep disorders has grown, studies on sleep quality are increasingly required. Recent evidence suggests that calcium intake may influence sleep quality and duration, but few studies have investigated factors associated with sleep quality. This systematic review aimed to examine and synthesise existing evidence on the association between calcium intake and sleep quality and sleep duration. Methods: We searched randomised controlled trials, case-control studies, cohort studies and cross-sectional studies from multiple databases, including PubMed, Web of Science, Cochrane Library, Scopus and CINAHL Plus, followed by keyword search at Google Scholar and reference review of included articles. Results: A total of seven independent studies presented in nine reports met the inclusion criteria. Six of them were cross-sectional studies. The studies suggested a positive association between calcium intake and sleep quality, although the results were not statistically significant in some cases. Studies also indicated that lower calcium intake was associated with inappropriate sleep duration. We decided not to conduct a meta-analysis because of the insufficient number of studies. Conclusion: The findings suggest a potential positive relationship between calcium intake and sleep quality, though the quality of evidence is unsatisfactory. To test the effectiveness of calcium intake on sleep quality, a randomised controlled trial is required, including many countries from different regions.