Influence of a perpetual-daylight Arctic environment on periodicity in human cholesterol synthesis.

To identify factors associated with control of human cholesterol synthesis, periodicity in cholesterogenesis, hormonal levels and food consumption behavior were examined in 5 healthy individuals at the beginning and end of 18 d in a perpetual daylight Arctic environment devoid of time cues. At d 2 (phase I) and d 16 (phase II), cholesterol fractional synthesis rate was determined at 6 h intervals over 30 h as deuterium incorporation into plasma free cholesterol. Total plasma cholesterol, insulin and glucose-dependent insulinotropic polypeptide were also measured at each timepoint. Food intake and sleeping patterns were recorded prior to and during each phase. Cholesterol fractional synthesis rate (FSR) exhibited periodicity in all subjects on each phase, but did not differ between phase I (FSR rate = 0.038 +/- 0.038 pools.d-1) and phase II (FSR rate = 0.037 +/- 0.072 pools.d-1) phases. Phase II FSR period length was associated with both the duration between first and last meals (r2 = 0.81, p = 0.037) and total hours spent awake (r2 = 0.99, p = 0.001). Insulin and glucose-dependent insulinotropic polypeptide levels were not associated with FSR periodicity. These results suggest that meal timing and sleep/wake cycles are more important factors than insulin and glucose-dependent insulinotropic polypeptide in controlling the rhythms of whole body cholesterol synthesis.