The appropriate limit to the amount of daily sedentary time (ST) required to minimize mortality is uncertain. This meta-analysis aimed to quantify the dose-response association between daily ST and all-cause mortality and to explore the cut-off point above which health is impaired in adults aged 18–64 years old. We also examined whether there are differences between studies using self-report ST and those with device-based ST. Prospective cohort studies providing effect estimates of daily ST (exposure) on all-cause mortality (outcome) were identified via MEDLINE, PubMed, Scopus, Web of Science, and Google Scholar databases until January 2018. Dose-response relationships between daily ST and all-cause mortality were examined using random-effects meta-regression models. Based on the pooled data for more than 1 million participants from 19 studies, the results showed a log-linear dose-response association between daily ST and all-cause mortality. Overall, more time spent in sedentary behaviors is associated with increased mortality risks. However, the method of measuring ST moderated the association between daily ST and mortality risk (p < 0.05). The cut-off of daily ST in studies with self-report ST was 7 h/day in comparison with 9 h/day for those with device-based ST. Higher amounts of daily ST are log-linearly associated with increased risk of all-cause mortality in adults. On the basis of a limited number of studies using device-based measures, the findings suggest that it may be appropriate to encourage adults to engage in less sedentary behaviors, with fewer than 9 h a day being relevant for all-cause mortality.

A number of cross-sectional studies have suggested that higher levels of sedentary behavior (SB) are associated with worse cognitive abilities in older age. There is a paucity of longitudinal studies investigating this relationship utilizing objectively assessed SB. This study investigated the relationship between objectively assessed SB and future cognitive abilities in a cohort of older adults. A longitudinal study over 22.12±1.46months including 285 community-dwelling older adults across 14 regions in Taiwan was undertaken. Cognitive ability was ascertained using a Chinese version of the Ascertain Dementia 8-item Questionnaire (AD8) and SB captured by 7days accelerometer data. Multivariable negative binomial regression models adjusted for confounders were undertaken. 274 community-dwelling older adults finished the study (age=74.6±6.2, % female=54.4%). At baseline, 20.1% (n=55), 48.5% (n=133) and 31.4% (n=86) of the sample engaged in high (11+h), medium (7-10.99h) and low (<7h) of SB respectively. In the fully adjusted model, higher levels of SB were associated with an increased risk of worse cognitive ability at follow up (adjusted rate ratio (ARR)1.09 (95%CI:1.00-1.19)), with the strongest relationship evident in those engaging in over 11h of SB (ARR 2.27 (95%CI:1.24-4.16)). The relationship remained evident after adjusting for depressive symptoms and physical activity. Our data suggests that objectively assessed SB, particularly when over 11h a day, is independently associated with worse cognitive ability over a two year period. Our data adds to the pressing reasons to reduced SB in older age.

Background: This meta-analysis aimed to estimate the shape of the dose-response association between objectively-assessed daily sedentary time (ST) and all-cause mortality, and to explore whether there is a threshold of ST above which there is an increase in mortality risk in older adults. Methods: Searches for prospective cohort studies providing effect estimates of daily ST (exposure) on all-cause mortality (outcome) were undertaken in five databases up to 31 March 2019. A random-effects meta-regression model was conducted to quantify the dose-response relationship between daily ST and all-cause mortality. Sensitivity analyses were also performed to test the stability of the results. Results: Our analysis of pooled data from 11 eligible studies did not reveal a consistent shape of association between ST and mortality. After excluding three studies with potential confounding bias, there was a log-linear dose-response relationship between daily ST and all-cause mortality. Overall, higher amounts of time spent in sedentary behaviors were associated with elevated mortality risks in older adults. Visual assessments of dose-response relationships based on meta-regression analyses indicated that increased mortality risks became significant when total ST exceeded approximately 9 h/day. Conclusions: Based on a limited number of studies, this meta-analysis provides a starting point for considering a cut-off of daily sedentary time, suggesting older adults spend less time in daily sitting.