Effects of Chronic Caffeine Administration on Blood Glucose Levels and on Glucose Tolerance in Healthy and Diabetic Rats

OBJECTIVE: To analyse the effect of chronic caffeine use on risk reduction and prognosis of diabetes mellitus. METHODS: In this 60-day study, five groups of 11 healthy male Wistar rats were selected to receive one of four doses (37.5, 56.2, 75.0 or 93.0 mg/kg per day) of caffeine orally or no caffeine (control). The effect of caffeine on glycaemia and glucose tolerance was evaluated. After 15 days, each group was treated with 60 mg/kg of streptozotocine to induce diabetes mellitus, and glycaemia and glucose tolerance were assessed for a further 45 days. RESULTS: In nondiabetic rats, caffeine had no effect on blood glucose. Compared with controls, the fasting blood glucose levels declined significantly in two caffeine-treated groups (93.0 mg/kg per day and 56.2 mg/kg per day) during the first 15 days following diabetes induction. Glucose tolerance was significantly improved 120 min after glucose loading in all caffeine-treated groups. The mean ± SE half-maximal effective concentration of caffeine was 35.79 ± 2.44 mg/dl. CONCLUSIONS: Blood glucose levels decreased, and glucose tolerance improved, in diabetic rats administered increasing doses of caffeine.