Sedentary time as predictor of insulin resistance, independent of moderate or vigorous physical activity
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Both skeletal muscle mass/phenotype and fat mass/distribution modulate insulin sensitivity, while sedentary lifestyle is a behavioural variable which markedly influences body composition. This population-based study involving 376 middle-aged adults aimed to examine the prospective association between objectively-measured time spent sedentary and insulin resistance, and whether this association was independent of moderate and vigorous physical activity (MVPA). Duration of follow-up was 5.6 years. At both baseline and follow-up, physical activity and sedentary time were measured individually using calibrated minute-by-minute heart rate (HR) monitoring. Sedentary time was computed as the HR observations (minutes) below an individually predetermined threshold, and expressed as a percentage of total monitored time during waking hours over 4 days. MVPA was expressed as the percentage of time spent above 1.75 x resting HR. Fasting plasma insulin was used as a surrogate measure of insulin resistance, as reciprocal fasting insulin captures insulin sensitivity in non-hyperglycaemic states. Independent of other confounding factors and follow-up time, time spent sedentary at baseline was significantly and positively associated with log fasting insulin at follow-up. When further adjusting for MVPA, this association was strengthened. According to these results, time spent sedentary predicts higher levels of fasting insulin, independent of the amount of time spent at moderate and vigorous intensity activity levels, thus stressing the importance of reducing sedentary time on top of increasing MVPA in order to improve metabolic health.
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