Acute caffeine ingestion reduces insulin sensitivity in healthy subjects: a systematic review and meta-analysis

Systematic review and meta-analysis of 7 randomized controlled trials involving 70 healthy adults without diabetes. Participants were mostly young, lean, non-smoking men, although some trials included sedentary and obese adults; studies used either hyperinsulinemic-euglycemic clamp or OGTT-based indices to assess insulin sensitivity.

This systematic review evaluated acute caffeine exposure, most often as single oral doses of 4.45 to 6 mg/kg or 5 mg/kg, with one intravenous dose of 3 mg/kg and one caffeinated coffee condition. Interventions were compared with placebo or decaffeinated coffee in short-term randomized crossover trials.

Acute caffeine ingestion reduced insulin sensitivity in healthy subjects. Across trials, the pooled insulin sensitivity index was lower with caffeine versus placebo or control (SMD -2.06, 95% CI -2.67 to -1.44; I2 = 49%; P for heterogeneity = 0.07). The authors concluded that short-term caffeine exposure may shift glycemic homeostasis toward hyperglycemia and that longer-term trials are needed to understand chronic effects and coffee's potential anti-diabetic role.

The evidence base was small, with only 7 short-term trials and 70 participants total. Trials were heterogeneous in caffeine form, route, dose, and insulin sensitivity measurement method, and the population was narrowly limited to mostly young, healthy, male participants, reducing generalizability. Arm-level dietary, ethnicity, and adverse-event data were not reported in the provided text.