Caffeine Before Oral Glucose Tolerance Test Impairs Blood Glucose

Caffeine ingestion negatively affects insulin sensitivity during an oral glucose tolerance test (OGTT). The effects of caffeine ingestion on insulin and glucose homeostasis in obese men with type 2 diabetes was examined. Men 2 diabetes (age = 49 ± 2 y, BMI = 32 ± 1 kg/m2) underwent 2 trials, 1 wk apart, in a randomized, double-blind design. Each trial was conducted after withdrawal from caffeine, alcohol, exercise, and oral hypoglycemic agents for 48 h and an overnight fast. Subjects randomly ingested caffeine (5 mg/kg body weight) or placebo capsules and 1 h later began a 3 h 75 g OGTT. Caffeine increased serum insulin, proinsulin, and C-peptide concentrations during the OGTT relative to placebo. Insulin area under the curve was 25% greater after caffeine than after placebo ingestion. Despite this, blood glucose concentration was also increased in the caffeine trial. After caffeine ingestion, blood glucose remained elevated at 3 hour post glucose load compared with baseline
The insulin sensitivity index was lower (14%) after caffeine than after placebo ingestion. Overall, despite elevated and prolonged proinsulin, C-peptide, and insulin responses after caffeine ingestion, blood glucose was also increased, suggesting an acute caffeine-induced impairment in blood glucose management in men with type 2 diabetes.

The American Society for Nutritional Sciences J. Nutr. 134:2528-2533, October 2004

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