Light Physical Activity Relates to Insulin Sensitivity and Earlier Time of Day in Metabolic Syndrome

PURPOSE: Low insulin sensitivity is linked to metabolic syndrome (MetS). However, whether the time of day when light physical activity (LPA) occurs affects insulin sensitivity is unclear. We tested the relationship between LPA time of day and insulin sensitivity in MetS. METHODS: Thirty adults with MetS were classified as morning (MOR, n = 11, 9F), midday (MID, n = 9, 6F), or afternoon (AFT, n = 10, 6F) by active LPA time using 7-d tri-axial hip-worn accelerometry (Actigraph). Time of day was defined by which part of the day had the highest percentage (>50%) of LPA. Peripheral insulin sensitivity (M-value between 90-120 min) was measured using a 2-hr hyperinsulinemic-euglycemic clamp (40 mU/m2/min, 90 mg/dl), while hepatic (HOMA-IR), and adipose (Adipose-IR) insulin resistance were estimated from fasting glucose, FFA, and insulin, respectively. Aerobic fitness (VO2max), anthropometrics (BMI, waist circumference), and inflammation (TNF-α, CRP and IL-8 at 0 and 120 min) were also examined. RESULTS: There were no differences amongst groups in age (P = 0.60), ATP III criteria (P = 0.91), or VO2max (P = 0.76). While time in sedentary (P = 0.44) and moderate-to-vigorous activity (P = 0.66) were similar amongst groups, MOR (21.3 ± 1.7%, P = 0.03) and MID (21.1 ± 1.3%, P = 0.01) had increased time in LPA compared to AFT (16.5 ± 1.2%). Further, MOR had a lower BMI (33.1 ± 1 vs. 38.6 ± 1.8 vs. 41 ± 2 kg/m2, P = 0.004) and waist circumference (107.9 ± 1.8 vs. 115.3 ± 3.8 vs. 123.1 ± 5.4 cm, P = 0.02). Although clamp-derived insulin sensitivity (P = 0.43), HOMA-IR (P = 0.30), and adipose-IR (P = 0.81) were similar across groups, higher LPA (%) related to increased peripheral insulin sensitivity (r = 0.33, P = 0.04) and lower adipose-IR (r = -0.36, P = 0.02). There were no group differences in fasting or change (i.e. 120-0 min) in TNF-α (P = 0.55), CRP (P = 0.41) or IL-8 (P = 0.07). However, higher LPA (%) related to insulin stimulated reductions in IL-8 (r = -0.42, P = 0.01). These changes in IL-8 also correlated with a higher adipose-IR (r = 0.37, P = 0.03). CONCLUSION: Time spent in LPA relates to insulin sensitivity and earlier times of day. Future work should look at whether time of day influences body weight regulation and cardiovascular health to optimize disease prevention/treatment. Funding: NIH RO1-HL130296