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 <or= 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 >or= 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.