Effects of Coffee Consumption on Fasting Blood Glucose and Insulin Concentrations
Randomized controlled trials in healthy volunteers
- 1Department of Nutrition and Health, Faculty of Earth and Life Sciences, Vrije Universiteit, Amsterdam, the Netherlands
- 2Physiological Sciences Department, TNO Nutrition and Food Research, Zeist, the Netherlands
- 3Wageningen Center for Food Sciences, Nutrition and Health Program, Wageningen, the Netherlands
- 4Division of Human Nutrition, Wageningen University and Research Center, Wageningen, the Netherlands
- Address correspondence and reprint requests to Dr. R.M. van Dam, Department of Nutrition and Health, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, de Boelelaan 1085, 1081 HV Amsterdam, Netherlands. E-mail:
Higher habitual coffee consumption was associated with higher insulin sensitivity (1) and a lower risk for type 2 diabetes (2–6) in diverse populations. In contrast, short-term metabolic studies showed that caffeine intake can acutely lower insulin sensitivity (7–9) and increase glucose concentrations (10–15). Randomized intervention studies are needed to examine whether tolerance to these acute effects develops after longer-term consumption (16). We therefore examined the effects of coffee and caffeine on fasting blood concentrations of glucose and insulin over 2–4 weeks in two crossover studies in healthy volunteers.
RESEARCH DESIGN AND METHODS
The studies were approved by the TNO Nutrition and Food Research Medical Ethics Committee, and all participants gave informed consent. The trials were originally designed to study the effects of coffee and caffeine on plasma concentrations of homocysteine, and the study designs have been reported in detail previously (17,18). Participants were regular coffee consumers (more than five cups/day) and did not have known diabetes.
The first study was a 4-week crossover study that compared the effects of regular paper-filtered coffee consumption with that of coffee abstinence. A total of 40 volunteers used 1 l of coffee (70 g coffee grounds) for 4 weeks and abstained from coffee for 4 weeks in random order. Fourteen participants did not complete the trial because of nausea and restlessness (n = …