Caffeine Impairs Diabetics' Insulin, Glucose Function

GUELPH, Ontario--Scientists from the University of Guelph examined the effects of caffeine ingestion on insulin and glucose homeostasis in obese men with Type II diabetes. The randomized, double blind design involved 12 Type II diabetic men with a median age of 49 and with a body mass index (BMI) equal to 32 ± 1 kg/m2. The men underwent two trials, one week apart. Each trial was conducted after a 48-hour withdrawal from caffeine, alcohol, exercise and oral hypoglycemic agents followed by an overnight fast. Subjects then randomly ingested caffeine (5 mg/kg body weight) or placebo capsules and one hour later began a three-hour, 75 g oral glucose tolerance test (OGTT).

Caffeine ingestion increased serum insulin, proinsulin and C-peptide concentrations during the OGTT relative to placebo. Insulin area under the curve was 25 percent greater after caffeine ingestion than after placebo ingestion.

Blood glucose concentration also increased in the caffeine trial. After caffeine ingestion, blood glucose remained elevated at three hours post-glucose load (8.9 ± 0.7 mmol/L) compared with baseline (6.7 ± 0.4 mmol/L). The insulin sensitivity index also was lower (14 percent) after caffeine than after placebo ingestion.

The scientists concluded their findings suggest caffeine impairs blood glucose management in men with Type II diabetes. The study was published in the October issue of the Journal of Nutrition (134:2528-2533, 2004) (www.nutrition.org).