Research on physical activity and health has pointed clearly to increasing the time that adults spend doing moderate to vigorous intensity activities: 30 minutes a day is generally recommended. However, recent evidence underlines the importance of also focusing on sedentary behaviours—the high volumes of time that adults spend sitting in their remaining “non-exercise” waking hours. We provide a brief overview of recent evidence for the distinct relationships between ‘too much sitting’ and biomarkers of metabolic health and, thus, with increased risk of type 2 diabetes, cardiovascular disease and other prevalent chronic health problems. Particular concerns for this new field include the challenges of changing sedentary behaviours in the context of ubiquitous environmental and social drivers of sitting time; examining the effects of interventions for reducing or breaking-up sitting time and identifying the most relevant implications for clinical and public health practice.

Increasing participation in leisure time physical activity (LTPA) in adult populations is a central tenet of strategies for preventing major chronic diseases (type 2 diabetes, cardiovascular disease, breast and colon cancer) and obesity in developed and developing nations.1 2 To date, clinical practice, community programmes, mass-media campaigns and population strategies have focused mainly on encouraging and supporting individuals to be more active, largely during discretionary or leisure time, but more recently (and to a lesser extent) also in travel time.2 While these approaches have met with some success, our recent body of work has identified sedentary behaviour (time spent sitting) as a novel and potentially important risk factor for the development of chronic disease. Even if people meet the current recommendation of 30 minutes of physical activity on most days each week, there may be significant adverse metabolic and health effects from prolonged …