Acute caffeine ingestion does not impair glucose tolerance in persons with tetraplegia

Acute caffeine (Caf) ingestion impairs glucose tolerance in able-bodied humans during an oral glucose tolerance test (OGTT). The mechanism responsible for this effect remains unclear, however, it is suggested to be due to the accompanying increase in epinephrine concentration. We examined whether or not Caf would elicit a glucose intolerance in persons with tetraplegia (TP) who do not exhibit an increased epinephrine response following Caf ingestion. All TP [ n = 14; 9 incomplete (Inc) lesion, 5 complete (Com) lesion] completed two OGTT 1 h after consuming either gelatin (Pl) or Caf capsules (dose = 4 mg/kg). Blood samples were collected at baseline (time = 0 min), 1 h after capsule ingestion (time = 60 min), and every 30 min during the OGTT (time = 90–180 min). Glucose, insulin, proinsulin, and C-peptide responses were similar ( P > 0.05) between treatments, demonstrating no effect of Caf on glucose tolerance. This lack of a Caf effect may be due to the low epinephrine concentration that remained unchanged ( P > 0.05) throughout all experiments. Interestingly, the Com exhibited a 50% higher glucose response ( P ≤ 0.05) and a 46% ( P > 0.05) lower insulin response (vs. Inc), suggesting a more pronounced glucose intolerance within this subgroup. Furthermore, nine TP (5 Com, 4 Inc) had glucose levels of ≥ 7.8 mM at the end of the OGTT (time = 180 min), classifying them as glucose intolerant. In summary, acute Caf ingestion does not increase epinephrine concentration or impair glucose tolerance in TP.