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Physical behaviours and their association with type 2 diabetes risk in urban South African middle-aged adults: An isotemporal substitution approach

Introduction: To examine the associations between physical behaviours and type 2 diabetes mellitus (T2DM) risk in middle-aged South African men and women. Research design and methods: This cross-sectional study included middle-aged men (n=403; age: median [IQR], 53.0 [47.8 to 58.8] years) and women (n=324; 53.4 [49.1 to 58.1] years) from Soweto, South Africa. Total movement volume (average movement in milli-g) and time (minutes/day) spent in different physical behaviours, including awake sitting/lying, standing, light intensity physical activity (LPA) and moderate to vigorous intensity physical activity (MVPA), were determined by combining the signals from two triaxial accelerometers worn simultaneously on the hip and thigh. All participants completed an oral glucose tolerance test, from which indicators of diabetes risk were derived. Associations between physical behaviours and T2DM risk were adjusted for sociodemographic factors and body composition. Results: Total movement volume was inversely associated with measures of fasting and 2-h glucose and directly associated with insulin sensitivity, basal insulin clearance, beta-cell function, but these associations were not independent of fat mass, except for basal insulin clearance in women. In men, replacing 30 minutes of sitting/lying, standing or LPA with the same amount of MVPA time was associated with 1.2 to 1.4 mmol/L lower fasting glucose and 12.3 to 13.4 mgl2/mUmin higher insulin sensitivity. In women, substituting sitting/lying with the same amount of standing time or LPA was associated with 0.5 to 0.8 mmol/L lower fasting glucose. Substituting 30 minutes sitting/lying with the same amount of standing time was also associated with 3.2 mgl2/mUmin higher insulin sensitivity, and substituting 30 minutes of sitting/lying, standing or LPA with the same amount of MVPA time was associated with 0.25 to 0.29 ng/mIU higher basal insulin clearance in women. Conclusion: MVPA is important in reducing T2DM risk in men and women but LPA appears to be important in women only. Recommendations for PA may differ by sex.