Objectively Measured Sedentary Time May Predict Insulin Resistance Independent of Moderate- and Vigorous-Intensity Physical Activity

Diabetes, Aug 2009

OBJECTIVE To examine the prospective association between objectively measured time spent sedentary and insulin resistance and whether this association is independent of moderate- and vigorous-intensity physical activity (MVPA) and other relevant confounders. RESEARCH DESIGN AND METHODS This was a population-based study (Medical Research Council Ely study) in 376 middle-aged adults (166 men; 210 women) over 5.6 years of follow-up. Physical activity and sedentary time were measured objectively by individually calibrated minute-by-minute heart rate monitoring at both baseline and follow-up. Sedentary time was calculated as the heart rate observations (in minutes) below an individually predetermined threshold (flex heart rate) and expressed as a percentage of total monitored time during waking hours over 4 days. The percentage of time spent above 1.75 × resting heart rate represented MVPA. Fasting plasma insulin was used as a surrogate measure of insulin resistance. RESULTS Time spent sedentary at baseline was significantly and positively associated with log fasting insulin at follow-up (β = 0.003, 95% CI 0.0006–0.006, P = 0.015) independent of baseline age, sex, fat mass, fasting insulin, smoking status, and follow-up time. After further adjustment for MVPA, this association was somewhat strengthened (β = 0.004, 95% CI 0.0009–0.006, P = 0.009). CONCLUSIONS Time spent sedentary predicts higher levels of fasting insulin independent of the amount of time spent at moderate- and vigorous-intensity activity levels. This highlights the importance of reducing sedentary time in order to improve metabolic health, possibly in addition to the benefits associated with a physically active lifestyle.

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Objectively Measured Sedentary Time May Predict Insulin Resistance Independent of Moderate- and Vigorous-Intensity Physical Activity

Hendrik J.F. Helmerhorst Katrien Wijndaele Sren Brage Nicholas J. Wareham Ulf Ekelund OBJECTIVE-To examine the prospective association between objectively measured time spent sedentary and insulin resistance and whether this association is independent of moderate- and vigorous-intensity physical activity (MVPA) and other relevant confounders. RESEARCH DESIGN AND METHODS-This was a population-based study (Medical Research Council Ely study) in 376 middle-aged adults (166 men; 210 women) over 5.6 years of follow-up. Physical activity and sedentary time were measured objectively by individually calibrated minute-by-minute heart rate monitoring at both baseline and follow-up. Sedentary time was calculated as the heart rate observations (in minutes) below an individually predetermined threshold (flex heart rate) and expressed as a percentage of total monitored time during waking hours over 4 days. The percentage of time spent above 1.75 resting heart rate represented MVPA. Fasting plasma insulin was used as a surrogate measure of insulin resistance. RESULTS-Time spent sedentary at baseline was significantly and positively associated with log fasting insulin at follow-up ( 0.003, 95% CI 0.0006 - 0.006, P 0.015) independent of baseline age, sex, fat mass, fasting insulin, smoking status, and follow-up time. After further adjustment for MVPA, this association was somewhat strengthened ( 0.004, 95% CI 0.0009 - 0.006, P 0.009). CONCLUSIONS-Time spent sedentary predicts higher levels of fasting insulin independent of the amount of time spent at moderate- and vigorous-intensity activity levels. This highlights the importance of reducing sedentary time in order to improve metabolic health, possibly in addition to the benefits associated with a physically active lifestyle. Diabetes 58:1776-1779, 2009 - I nsulin resistance is a precursor of type 2 diabetes and a major characteristic of the metabolic syndrome (1). Hyperinsulinemia and impaired insulin sensitivity are common clinical findings yielding independent health risks, including metabolic, cardiovascular, and neoplastic disorders (2 4). Several etiological factors have been identified for impaired insulin sensitivity, including genotype, body composition, inflammation, and lifestyle factors (57). Low levels of physical activity and lack of moderate- and vigorous-intensity physical activity (MVPA) are associated with insulin resistance (8,9). Sedentary time has been linked to various cardiometabolic health outcomes, sometimes independent of overall physical activity in cross-sectional analyses (10 12). Because the cardiometabolic consequences are suggested to be a unique feature in hazardous physical activity behavior, sedentary behavior should be considered distinctively from physical activity when examining associations with these health outcomes (13). A recent prospective analysis suggested that MVPA but not sedentary time was associated with insulin resistance in high-risk individuals over a 1-year follow-up period (14). Further prospective research is needed to examine these associations and the direction of causality in normal-risk populations with longer duration of follow-up. Therefore, the purpose of the present study was to 1) examine the prospective association between objectively measured sedentary time and fasting insulin, a marker of insulin resistance, in healthy middle-aged Caucasian subjects and 2) examine whether this association is independent of MVPA and other confounding variables. RESEARCH DESIGN AND METHODS This study is part of the Medical Research Council Ely study, a prospective population-based cohort study of the etiology and pathogenesis of type 2 diabetes and related metabolic disorders. Data were collected in 1994 1996 (baseline) and again in 20012003 (median follow-up time 5.6 years). A total of 393 participants with complete data on anthropometry, body composition, and physical activity energy expenditure (PAEE) at both baseline and follow-up were initially selected (15). Participants with missing data on fasting plasma insulin, fat mass, smoking status, or MVPA were excluded. Therefore, the present report comprises 376 (166 male) healthy middle-aged Caucasian subjects. Missing data were random with respect to body composition and physical activity at baseline. Ethics permission for the study was granted by the Cambridge Local Research Committee, and all participants provided written informed consent. Plasma insulin, glucose, and confounding variables. Data collection procedures have been described in detail previously (9,16). In brief, blood samples were taken after an overnight fast. Plasma insulin and glucose levels were determined using standardized protocols. Levels of fasting plasma insulin were used as a surrogate measure for insulin resistance. The homeostasis model assessment of insulin resistance (HOMA-IR) score was calculated by dividing the product of fasting plasma insulin (microunits per milliliter) and fasting (...truncated)


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Hendrik J.F. Helmerhorst, Katrien Wijndaele, Søren Brage, Nicholas J. Wareham, Ulf Ekelund. Objectively Measured Sedentary Time May Predict Insulin Resistance Independent of Moderate- and Vigorous-Intensity Physical Activity, Diabetes, 2009, pp. 1776-1779, 58/8, DOI: 10.2337/db08-1773