Impaired glucose tolerance in patients with narcolepsy

Recent studies have focused on the interaction between sleep regulation and metabolism, owing to the important role of the orexin system in sleep regulation and pathophysiology of narcolepsy. To address this issue we performed glucose tolerance tests in narcoleptic patients. We have examined 7 male and 2 female patients with narcolepsy and cataplexy (mean age 34.4±10.8y; mean BMI 25.8±3.2kg/m2) and 9 healthy controls matched for sex, age and BMI. Blood glucose, insulin, HbA1c, cortisol, ACTH, cholesterol, triglyceride levels were assessed. At 0800h the subjects were offered either a 75g/300ml glucose or a similar sorbitol sweetened drink, followed by drawing blood samples for glucose at 0, 30, 60, 120, 180, 240min. 4 of the 9 narcoleptic but no healthy subjects had a 120min blood glucose level above 140mg/dl indicating a pathological glucose tolerance. The AUC for the glucose condition was significantly higher in patients suffering from narcolepsy than in healthy controls (28248.3 vs. 25676.7min·mg/dl; t[8]=2.662; p=0.029; effects size d=0.8). The percentage of HbA1c was found to be significant higher in narcoleptic patients than in controls (5.41% vs. 5.01%, t[8]=2.353; p=0.049; effects size d=0.7), however the other metabolic and endocrine parameters did not differ between the groups. The glucose tolerance in narcoleptic patients is impaired. HbA1c shows a slight but significant increase in that group. Disturbed glucose metabolism might be a genuine feature of narcolepsy.