Background Circadian rhythm is altered in individuals with obesity and insulin resistance, showing a smaller amplitude, less stability, and increased intradaily variation. Objective We compared reproducibility of circadian-rhythm parameters over time and under free-living vs. controlled conditions in participants with obesity and pre-diabetes after 2- and 3-year weight-loss maintenance during the 3-year PREVIEW (PREVention of diabetes through lifestyle intervention and population studies In Europe and around the World) study. Associations of obesity and insulin resistance with circadian-rhythm parameters were assessed. Subjects and methods Circadian-rhythm parameters were determined using continuous wrist-temperature measurements in free-living environments at year 2 (n = 24; age 56.8 +/- 10.3 y; body mass index (BMI) = 30 +/- 3.9 kg/m(2); homeostatic model assessment of insulin resistance (HOMA-IR) 2.4 +/- 1.1), at year 3 (n = 97; age 61.7 +/- 7.8; BMI = 29.7 +/- 3.9; HOMA-IR 2.9 +/- 2.1), and at year 3 in a controlled condition (n = 38; age 63.4 +/- 6.7; BMI = 28.7 +/- 3.9; HOMA-IR 3.8 +/- 1.4). Reproducibility was assessed by analyzing repeatability coefficients (CR), differences, and associations, over time as well as between conditions. Associations of BMI and HOMA-IR with circadian-rhythm parameters were assessed at y-3 in both conditions using factor analysis, followed by Pearson's correlations. Results Reproducibility of circadian-rhythm parameters over time in the free-living environments was high (CR 0.002-5.26; no significant differences; associated amplitudes r = 0.57; p < 0.01). In contrast, reproducibility between different conditions was low (CR 0.02-11.36; significant differences between most parameters (p < 0.05); yet associated amplitudes r = 0.59; p < 0.01). In the controlled vs. free-living condition circadian-rhythm was more stable; BMI and HOMA-IR were associated with the physiological amplitude-related parameters (r = -0.45; p < 0.01; r = -0.33; p < 0.05). In the free-living environment, BMI and behavioral circadian-rhythm parameters indicating circadian alignment, contributed most to the explained variation (47.1%), and were inversely associated (r = -0.22; p < 0.05), while HOMA-IR was inversely associated with stability-related circadian-rhythm parameters (r = -0.21; p < 0.05). Conclusions Circadian rhythm was highly reproducible over time in the free-living environments, yet different under different conditions, being more stable in the controlled condition. BMI may play a significant role in circadian alignment and vice versa in the free-living environment.
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