Sedentary Behaviour and Cardiovascular Disease

Sedentary behaviour is ubiquitous in high-income countries and increasingly so in low- to middle-income countries. Sedentary behaviour research has made substantial progress in the last 15 years, including a consensus on the definition of sedentary behaviour, the development and standardisation of methods that acknowledge displacement effects and a plethora of mechanistic studies. Despite such progress, our understanding of the independent effects of sedentary behaviour on cardiovascular health and cardiovascular disease occurrence is still incomplete. Multiple methodological and interpretational issues hinder a confident translation of available research into interventions and guidelines aimed at the primary prevention of cardiovascular disease. Such issues include a paucity of prospective longitudinal studies measuring actual posture, the influence of pre-existing illness and reverse causation, the dependence of sedentary behaviour effects on physical activity levels, the exaggerated benefits of replacing siting with standing and the causal interpretations of poor sedentary behaviour markers such as television viewing. In young people, the overwhelming majority of the evidence examining the links between objectively assessed sedentary behaviour and surrogate markers of cardiovascular health is cross-sectional and the few prospective studies point towards no associations. The best available epidemiological evidence on self-reported sitting time in adults suggests that the risk for incident cardiovascular disease is elevated at around 10 h/day and over. Considering that self-reported measures underestimate actual sitting times considerably, it is likely that the ‘true’ threshold is higher. The causality of sitting time and cardiovascular disease is far from established. Besides, the biological mechanisms that would explain any ‘independent’ effect of sitting time are not proven in humans, despite a plethora of proposed hypotheses (e.g. endothelial damage, lipoprotein lipase activation). The association between high sedentary time and cardiovascular disease appears to be modified by physical activity; equivalents of approximately 45–60 minutes of moderate intensity activity per day appear to largely offset cardiovascular events risk. Since such an amount of daily physical activity may be beyond the reach of large parts of the population, advocates of the sedentary behaviour paradigm recommend to replace sitting with physical activity of any intensity for cardiovascular health benefits, particularly among the most physically inactive middle aged and older population groups and those who are likely to be resistant or unable to increase physical activity of moderate-to-vigorous intensity. Further research efforts are warranted for optimising the device-based measurement of sedentary behaviour in large-scale observational studies and consortia, for understanding better its independent cardiovascular effects and mechanisms of action – if any such mechanisms exist.