Abstract
OBJECTIVES: This scoping review summarizes and evaluates evidence from Japan on prospective relationships of sedentary behavior (too much sitting, as distinct from too little physical activity) with health outcomes, forming the basis for Japan's new sedentary behavior guidelines. It also identified evidence gaps and provided recommendations for future public health guidelines. METHODS: A systematic search was conducted in PubMed, Web of Science, CINAHL, and MEDLINE for English-language, peer-reviewed longitudinal studies on sedentary behavior and health outcomes in apparently healthy Japanese adults published between 2000 and 2023. The search strategy was developed based on sedentary behavior measures, study design, and study population. Two independent reviewers screened titles, abstracts, and full texts. Data were synthesized narratively, with a quality assessment performed. RESULTS: Twenty-seven relevant studies were identified, all but one published after 2013. About half focused on middle-aged and older adults, primarily using self-report questionnaires. Many studies were large cohorts (>10,000 participants) with follow-ups of more than 10 years. Studies varied widely in physical activity indicators, confounders, time classifications, and cutoff values for sedentary behavior. The studies examined 29 health outcomes, primarily all-cause mortality, cancer incidence, and cancer mortality. Most studies reported at least partial evidence of harmful associations between sedentary behavior and health outcomes, though only eight were rated as good quality. CONCLUSION: There is sufficient evidence to support minimizing sedentary time to promote health in Japanese adults. However, due to the limited number of high-quality studies, the specificity and dose-response relationship between sedentary behavior and health outcomes remain unclear.