Morning coffee is a common remedy following disrupted sleep yet each factor can independently impair glucose tolerance and insulin sensitivity in healthy adults. Remarkably, the combined effects of sleep fragmentation and coffee on glucose control upon waking per se have never been investigated.
In a randomised cross-over design, 29 adults (Mean ± SD; age: 21 ± 1 years, BMI: 24.4 ± 3.3 kg·m-2) underwent three oral glucose tolerance tests (OGTT). One following a habitual night of sleep (Control; in bed, lights-off trying to sleep ~2300-0700 h) the others following a night of sleep fragmentation (as Control but waking hourly for 5 min), once with and once without morning coffee ~1 h after waking (~300 mg caffeine as black coffee 30 min prior to OGTT).
Peak plasma glucose and insulin concentrations were unaffected by sleep quality but were higher following coffee consumption (Mean [normalised confidence interval] for Control, Fragmented, and Fragmented+Coffee, respectively; Glucose: 8.20 [7.93-8.47] mmol∙L-1versus 8.23 [7.96-8.50] mmol∙L-1versus 8.96 [8.70-9.22] mmol.L-1; Insulin: 265 [247-283] pmol∙L-1; and 235 [218-253] pmol∙L-1; and 310 [284-337] pmol∙L-1). Likewise, iAUC for plasma glucose was higher in the Fragmented+Coffee trial compared to Fragmented.
Whilst sleep fragmentation did not alter glycaemic or insulinaemic responses to morning glucose ingestion, if a strong caffeinated coffee is consumed then a reduction in glucose tolerance can be expected.