title: Objectively measured sedentary time may predict insulin resistance independent of moderate- and vigorous-intensity physical activity.
abstract: 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.
  
  
  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 x 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 (beta = 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 (beta = 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.
authors.affiliation: Medical Research Council Epidemiology Unit, Cambridge, UK.
authors.forename: Hendrik J F
authors.initials: HJ
authors.lastname: Helmerhorst
authors.forename: Katrien
authors.initials: K
authors.lastname: Wijndaele
authors.forename: Søren
authors.initials: S
authors.lastname: Brage
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Wareham
authors.forename: Ulf
authors.initials: U
authors.lastname: Ekelund
mesh_terms: D000332:Aerobiosis; D001786:Blood Glucose / Q000378:metabolism; D001823:Body Composition; D015331:Cohort Studies; D004734:Energy Metabolism; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate; D006801:Humans; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000502:physiology*; D008019:Life Style; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D010809:Physical Fitness; D011446:Prospective Studies; D012146:Rest / Q000502:physiology*
chemical_list: D001786:Blood Glucose; D007328:Insulin