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BACKGROUND AND PURPOSE: Napping is a widespread practice worldwide and has in recent years been linked to increased abdominal adiposity. Lipase E or encodes the protein hormone-sensitive lipase (HSL), an enzyme that plays an important role in lipid mobilization and exhibits a circadian expression rhythm in human adipose tissue. We hypothesized that habitual napping may impact the circadian expression pattern of , which in turn may attenuate lipid mobilization and induce abdominal fat accumulation.METHODS: Abdominal adipose tissue explants from participants with obesity (n = 17) were cultured for a 24-h duration and analyzed every 4 h. Habitual nappers (n = 8) were selected to match non-nappers (n = 9) in age, sex, BMI, adiposity, and metabolic syndrome traits. Circadian expression rhythmicity was analyzed using the cosinor method.RESULTS: Adipose tissue explants exhibited robust circadian rhythms in expression in non-nappers. In contrast, nappers had a flattened rhythm. amplitude was decreased in nappers as compared with non-nappers (71% lower). The decrease in amplitude among nappers was related to the frequency of napping (times per week) where a lower rhythm amplitude was associated with a higher napping frequency (r = -0.80; = 0.018). Confirmatory analyses in the activity of 's protein (i.e., HSL) also showed a significant rhythm in non-nappers, whereas significance in the activity of HSL was lost among nappers.CONCLUSION: Our results suggest that nappers display dysregulated circadian expression as well as dysregulated circadian HSL activity, which may alter lipid mobilization and contribute to increased abdominal obesity in habitual nappers.