Caffeine Impairs Glucose Metabolism in Type 2 Diabetes

  1. James D. Lane, PHD,
  2. Christina E. Barkauskas, AB,
  3. Richard S. Surwit, PHD and
  4. Mark N. Feinglos, MD
  1. From the Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, North Carolina
  1. Address correspondence and reprint requests to James D. Lane, PhD, P.O. Box 3830, Duke University Medical Center, Durham, NC 27710-0001. E-mail: james.lane{at}

Caffeine is a widely used drug despite evidence that it has deleterious consequences for health, including diabetes (1). In 1967, a study reported that drinking two cups of instant coffee significantly impaired glucose tolerance in a small group of men with “maturity-onset diabetes” (2). Recent studies showed that caffeine acutely decreased insulin sensitivity in young, nondiabetic adults (3–5). This study tested how oral caffeine affects carbohydrate metabolism in patients with type 2 diabetes, for whom decreases in insulin sensitivity might result in exaggerated hyperglycemic responses to glucose and other carbohydrates, which would aggravate the glycemic dysregulation found in the disease. We tested the effects of caffeine on fasting glucose and insulin levels and on glucose and insulin responses to a mixed-meal tolerance test (MMTT).


The research protocol, approved by the medical center’s Institutional Review Board, employed a double-blind, placebo-controlled, cross-over design. The study group comprised of 14 habitual coffee drinkers (11 men and 3 women, age 61 ± 9 years [means ± SD]), who had at least a 6-month history of type 2 diabetes. Based on self-reports, daily caffeine intake from all beverages averaged 526 ± 144 mg/day. Mean fasting plasma glucose was 7.5 ± 1.6 mmol/l. Three of the subjects managed diabetes with diet and exercise, …

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