Purpose: Due to the increased use of screens (smartphone, TV, computer), sedentary (screen) behaviour has become increasingly visible in the lives today’s children and adolescents. The assumption that this has adverse health effects has led to screen time recommendations accompanying an explosion of preventive interventions targeting the reduction of screen and sedentary time. But, is there sufficient evidence justifying a quantitative recommendation for sedentary (screen) time in children and adolescents?

Methods: A scoping review was conducted in PubMed, summarizing studies on the association between sedentary behaviour and health indicators in children and adolescents (0-18 years). A broad search was conducted, including studies with various designs (cross-sectional, prospective, experimental) and with various physical and mental health outcomes. Findings are evaluated by critically considering the methodological quality of included studies.

Results: A number of methodological issues should be considered when examining the literature on potential adverse health effects of sedentary behaviour in children and adolescents. First, evidence is predominantly based on cross-sectional studies, that are obviously not able to distinguish cause and effect. Second, self- or proxy-reported TV viewing time is often used as an indicator of overall sedentary behaviour, while TV viewing is only one of the many sedentary behaviours that children and adolescents engage in. Third, mostly only total time spent in sedentary behaviour is considered – whether or not adjusting for physical activity, ignoring the pattern in which sedentary behaviour and physical activity are accumulated and alternated throughout the day and week. Prospective studies or studies using device-based sedentary behaviour report less consistent findings compared to cross-sectional studies and self- or proxy-reported sedentary behaviour.

Conclusions: The evidence regarding associations of childhood sedentary behaviour and health is inconsistent and varies across study design and type, measurement and analysis of sedentary behaviour. Future youth public health guidelines may need to address the accumulation and alternation of sedentary behaviour and physical activity throughout the day and week.

Purpose: While current sedentary behavior recommendations are typically stated in broad terms, the interplay of emerging evidence from observational and experimental studies may inform more sophisticated messaging, particularly with respect to chronic disease prevention and management. The purpose of this presentation will be to examine the collective evidence in adults, with a specific focus on population groups with heightened chronic disease risk.

Methods: The presentation will be informed by the evidence synthesis undertaken by the 2018 Physical Activity Guidelines Advisory Committee for the 2^ndEdition of the Physical Activity Guidelines for Americans, along with recent reviews we have published that have emphasized the importance of integrating evidence from observational and experimental research to better inform public health strategies. An example of how this evidence triangulation has led to new specific recommendations in the context of type 2 diabetes (T2D) management will be provided.

Results: There is strong evidence that exposure to high volumes of sitting time can significantly increase risk for all-cause and cardiovascular mortality, and incident CVD and T2D. The association between sedentary behavior and all-cause mortality can vary by the amount of moderate-to-vigorous physical activity, being much more pronounced in those who are inactive (i.e., not meeting physical activity guidelines). Interactions of sedentary behavior with physical activity for other health outcomes are not well understood. The concept of ‘breaks in sitting time’, shown in the early observational studies to have beneficial associations with cardiometabolic risk biomarkers, has since been pursued in laboratory trials comparing prolonged sitting to ‘sitting interruptions’ involving brief periods of postural change and/or physical activity. Notably, this experimental evidence has identified cardiometabolic risk benefits to be amplified in those with/at risk of developing T2D. The American Diabetes Association now recommends that at least in adults with T2D, ‘prolonged sitting should be interrupted with bouts of light activity every 30 minutes for blood glucose benefits’. 

Conclusion: Readiness for inclusion of more prescriptive ST recommendations is more advanced for clinical guidelines than for public health guidelines. Addressing the interplay between physical activity and sedentary behaviour will be key for future guideline development.

Purpose: Older adults are the fastest growing segment of the population, are the least likely to achieve minimum recommendations for physical activity, and accumulate the most sedentary time of any other age group. The purpose of this presentation is to examine the relationship between sedentary time (ST) and health, with a focus on outcomes of particular relevance to an older adult population.

Methods: The primary source of data for this presentation is a critical inspection of the literature, including an update to a published review (BJSM, 2017). Cross-sectional, longitudinal observational, and intervention studies were compared to determine if there is consistent evidence of a dose of ST that is associated with significant and meaningful outcomes. In light of estimates that > 65% of older adults have at least two chronic conditions, the outcomes of focus during this presentation will be cognitive function and mobility, as these are highly relevant to longevity and quality of life, even among those with multi-morbidity. Associations with time spent in different sedentary behaviours and breaks in ST were examined and the presentation will consider whether guidelines should focus on specific behaviours, total ST, or patterns of ST.

Results: ST  poses a unique problem for older adults by impacting mobility and cognitive function, thus increasing risk for disability in activities of daily living. There is evidence that suggests reducing ST by 1 hour/day could have clinically meaningful effects on health and mobility. Breaks in ST are positively associated with physical function among older adults, although the evidence is primarily cross-sectional.The type and context of ST may be important; some cognitively engaging sedentary behaviours appear to be associated with less risk of both physical and cognitive impairments compared to passive ST. The impact of ST is most significant among older adults with low physical activity.

Conclusion: Including ST in activity guidelines may be especially important for older adults given their relatively lower participation in physical activity. While guidelines for an optimal pattern of ST may be most appropriate based on the evidence, complicated public health messages have disadvantages that must be considered.