Objectively measured sedentary time may predict insulin resistance, independent of moderate and vigorous 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 physical activity (MVPA) and other relevant confounders.

Research Design and Methods: Population-based study (MRC 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 (HR) monitoring at both baseline and follow-up. Sedentary time was calculated as the HR observations (minutes) below an individually predetermined threshold (flex HR), 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 HR 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 (ß = 0.003, 95% CI: 0.0006 to 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 (ß = 0.004, 95% CI: 0.0009 to 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.