BackgroundThe 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.MethodsProspective 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.ResultsBased 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.ConclusionsHigher 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.Electronic supplementary materialThe online version of this article (10.1186/s12916-018-1062-2) contains supplementary material, which is available to authorized users.

CV fitness exhibits stronger longitudinal associations with academic performance than other forms of fitness or BMI for adolescents.

Objective (246/250)Physical activity (PA), especially moderate-to-vigorous intensity, could protect older adults from cognitive impairment. However, most literature is based on self-reported PA which is limited by recall bias. Light PA is popular among older adults, but a paucity of objective longitudinal data has considered the relationship between light PA and cognitive ability. We examined if a higher level of objectively measured light PA, independent of moderate-to-vigorous physical activity (MVPA), was prospectively associated with better cognitive ability in older adults. MethodsA longitudinal study over 22.12 (±1.46) months including 274 community-dwelling older adults across 14 regions in Taiwan was undertaken. Cognitive ability was obtained using a Chinese version of the Ascertain Dementia 8-item Questionnaire (AD8) and light PA and MVPA captured by 7 days accelerometer positioned on waist. Multivariable negative binomial regression adjusted for confounders were undertaken. ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T ConclusionOur data suggest that light PA may offer a protective influence of future cognitive ability in community dwelling older adults. The promotion of light PA may be a valuable means to maintain cognitive ability in older age.

These findings confirm an adverse effect of social isolation on the sleep quality of older adults, but indicate that this effect is independent of loneliness. Social isolation and loneliness seem to have distinct pathways in affecting the sleep quality of older adults.