Associations between sedentary behaviour patterns with body fatness in population-based study of Irish adults.

INTRODUCTION: Studies have reported accelerometer-derived sedentary (SED) time is adversely associated with waist circumference (WC), whilst the number of breaks from SED activities is inversely associated with WC. PURPOSE: To assess whether SED behaviour patterns, including characteristics of breaks, are cross-sectionally associated with WC and whole body fatness. METHODS: A nationally representative group of Irish adults (n=1111, 18-85yrs) wore a uni-axial accelerometer (Actigraph, GTM1) recording 5-sec epochs for 2-4 consecutive days. Removing non-wear times resulted in complete accelerometry data (≥600mins/d for 2 to 4 days) for 894 subjects. There were no significant differences between those with complete data and those without. Subjects taking medications affecting body composition or mobility were removed (n=10). Mean time (mins/day) spent in SED activities and moderate-to-vigorous intensity physical activity (MVPA) was determined using published cut-offs adjusted for epoch length. Number of breaks from SED, break duration and intensity of activity during breaks, number and length of bouts of MVPA ≥10 mins were also calculated.SED was adjusted for length of monitor wear time using a residual method. Waist circumference (WC) was measured and fat mass (kg) determined by bio-electrical impedance, and adjusted for height (fat mass index FMI, kg/m2 ). FMI was log-transformed using natural logs (logFMI). Relationships between MVPA and sedentary patterns with WC and logFMI were examined using multiple linear regression models adjusted for gender, age, smoking status and high alcohol intake and MVPA adjusted for wear time. RESULTS: Monitor mean daily wear time was 842.0 mins (SD 79.3). Majority was spent in SED (median 76.5% IQR (71.1, 81.0) with only median 5.4% spent in MVPA (IQR 3.7, 7.8). SED, break duration and activity intensity during breaks were all associated with WC and log FMI, but not number of breaks. MVPA was inversely associated with WC and logFMI (p<0.001), but not number or length of MVPA bouts. Waist circumference Fat mass index (kg/m2 ) Standardised β-coefficient Β (SE) Standardised β-coefficient Β (SE) SED 0.12 0.03 (0.09)* 0.12 0.001 (0.0003)* Break duration 0.14 35.3 (11.4)* 0.18 1.42 (0.36)* Break intensity -0.21 -2.62 (0.50)* -0.24 -0.09 (0.02)* Adjusted R2 26.3 25.0 *P<0.01 CONCLUSION: These analyses suggest that in a nationally representative group of adults where time spent in MVPA was low, SED behaviour patterns, including time spent in SED, length and intensity of activity in breaks, are associated with body fatness. Supported by Irish Department of Agriculture, Fisheries and Food; Food for Health Research Initiative