Caffeine ingestion elevates plasma insulin response in humans during an oral glucose tolerance test.
Level 2 - randomized trial
Individual double-blind randomized crossover trial
What was done
Eighteen young, fit adult males underwent two double-blind oral glucose tolerance tests (OGTT). Participants ingested either caffeine (5 mg/kg) or placebo 1 hour before consuming a 75 g dextrose load. Fasting and post-load serum insulin, C-peptide, blood glucose, lactate, fatty acids, glycerol, and plasma epinephrine were measured.
What was found
Baseline fasting levels of insulin, C-peptide, glucose, and lactate did not differ between conditions. Caffeine increased pre-OGTT serum fatty acids, glycerol, and plasma epinephrine (P <= 0.05). During the last 90 minutes of the OGTT, serum insulin and C-peptide were significantly higher in the caffeine trial (P <= 0.001); total area under the curve (AUC) was 60% greater for insulin (P <= 0.001) and 37% greater for C-peptide (P <= 0.001) compared with placebo. Blood glucose AUC was 24% higher after caffeine, but this difference was not statistically significant (P = 0.20).
Why it matters
This study demonstrates that acute caffeine ingestion substantially exaggerates the insulin response to a glucose challenge without improving glucose clearance, suggesting acute caffeine-induced insulin resistance.
Limits
The sample size was small (n = 18) and limited exclusively to young, fit men, preventing generalization to females or populations with insulin resistance. It examined only a single acute dose of pure caffeine rather than habitual intake or coffee ingestion.
Cited by
- supports Caffeine increases epinephrine levels, which in turn causes acute insulin resistance.