Energy expenditure in narcolepsy patients and controls

Abstract

Introduction Hypocretin deficiency causes narcolepsy, a condition characterized by excessive daytime sleepiness, cataplexy, and fragmented nocturnal sleep. Co-morbid overweight is present in two thirds of narcolepsy patients. Moreover one third of them is obese. Why narcolepsy patients gain weight is not known. They do not seem to eat and/or sleep more during 24 h than controls. This study was performed to detect a possible decrease in energy expenditure that could be the cause for the overweight in narcolepsy. This is the first study using a respiration chamber to measure Energy Expenditure in narcolepsy. Materials and methods Nine hypocretin deficient male patients with narcolepsy-cataplexy, and nine sex, age and body mass index (BMI) matched controls were enrolled. Energy Expenditure was measured for 24 h in a respiration chamber. Spontaneous physical activity was measured by a radar system based on Doppler principle. Subjects were given a diet to maintain energy balance based on the Harris–Benedict equation. Total Energy Expenditure (TEE), Overnight Metabolic Rate (OMR) and lowest Sleeping Metabolic Rate (SMRmin) were calculated. In addition, measured SMR was compared with SMR calculated with a prediction equation based on body composition. Results Narcolepsy patients did not differ from controls in BMI (27.4 ± 3.9 vs. 27.5 ± 4.2; P = 9.4) or age (38.1 ± 16.0 vs. 36.8 ± 15.2; P = .86) respectively. There were no differences in TEE (10.6 ± 1.2 vs. 10.6 ± .80 MJ/d; P = .99) OMR (5.7 ± .73 vs. 6.0 ± .55 MJ/d; P = .35), SMRmin (5.4 ± .76 vs. 5.4 ± .51 MJ/d; P = .99) and spontaneous activity between narcolepsy patients and matched controls (2862 ± 514 vs. 2732 ± 245 counts/d; P = .50). For both groups, measured SMR was closely related to SMR predicted from body composition. Conclusion Energy expenditure in narcolepsy patients is similar to matched controls. It is conceivable that we were not close enough to onset of the disease, when patients usually gain weight, to detect a possible difference before a new metabolic set point establishes. Acknowledgement This study was supported by a grant from UCB Pharma.