Physical activity, weight gain, and risk of mortality in adults

Abstract

<p><i>Why:</i> As low physical activity levels associate with ill health and mortality, continuous monitoring of physical activity levels is needed to inform policy. Identifying aetiology causes for the obesity epidemic is important to prevent population weight gain. However, there are still uncertainties on how physical activity and weight at population level associate over time, and how physical activity and sedentary time collectively influence premature death. <p><i>Aims and methods:</i> To describe prevalence of device-measured physical activity in adults (40-84 years) in the Seventh Tromsø Study survey 2015-16 (Tromsø7) (Paper I). To examine accelerometry-criterion validity for two physical activity questionnaires (PAQ)s and one sedentary time questionnaire (Paper II). To examine whether occupational (Paper III) and leisure time physical activity (Paper IV) changes from one examination to the next are associated with subsequent body mass index (BMI) changes from the second to a third examination, across Tromsø Study surveys from 1974 to 2016 in prospective cohort designs. To examine associations between device-measured physical activity, sedentary time, and mortality in a one-step individual participant data meta-analysis of four prospective cohort studies (Tromsø7, The Healthy Ageing Initiative 2012-2019, The Norwegian National Physical Activity Survey 2008-09, The National Health and Nutrition Examination Survey 2003-06) (Paper V). <p><i>Findings and conclusions:</i> About 70% of all adults met current lower-limit physical activity guidelines of 150 minutes per week of moderate and vigorous physical activity (Paper I). Processing PAQs in crude groups may attenuate biases associated with self-reported physical activity as it provided clearer patterns of higher device-measured physical activity by higher grouped ranking, while continuous scales of the PAQs showed small correlation magnitudes with device-measured physical activity (Paper II). Population levels of occupational (Paper III) and leisure time (Paper IV) physical activity appear insufficient to prevent weight gain but rather it appears the association is reverse, population weight gain leads to physical activity declines (Paper IV). Physical activity, at any intensity, associates with a substantial lower mortality risk and meeting current lower-limit guidelines ameliorates the higher mortality risk associated with high sedentary time (Paper V). <p><i>Importance:</i> This thesis highlights the public health gain of increasing population levels of physical activity, and of preventing population weight gain to avoid physical activity declines.