Coffee, Caffeine, and Risk of Type 2 Diabetes

A prospective cohort study in younger and middle-aged U.S. women

  1. Rob M. van Dam, PHD12,
  2. Walter C. Willett, MD134,
  3. JoAnn E. Manson, MD345 and
  4. Frank B. Hu, MD134
  1. 1Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts
  2. 2Department of Nutrition and Health, Faculty of Earth and Life Sciences, Vrije Universiteit of Amsterdam, Amsterdam, the Netherlands
  3. 3Department of Epidemiology, Harvard School of Public Health, Boston Massachusetts
  4. 4Channing Laboratory, Harvard Medical School and Brigham and Women’s Hospital, Boston, Massachusetts
  5. 5Division of Preventive Medicine, Harvard Medical School and Brigham and Women’s Hospital, Boston, Massachusetts
  1. Address correspondence to Rob M. van Dam, Department of Nutrition, Harvard School of Public Health, 665 Huntington Ave., Boston, MA 02115. E-mail: rvandam{at}hsph.harvard.edu

Abstract

OBJECTIVE—High habitual coffee consumption has been associated with a lower risk of type 2 diabetes, but data on lower levels of consumption and on different types of coffee are sparse.

RESEARCH DESIGN AND METHODS—This is a prospective cohort study including 88,259 U.S. women of the Nurses’ Health Study II aged 26–46 years without history of diabetes at baseline. Consumption of coffee and other caffeine-containing foods and drinks was assessed in 1991, 1995, and 1999. We documented 1,263 incident cases of confirmed type 2 diabetes between 1991 and 2001.

RESULTS—After adjustment for potential confounders, the relative risk of type 2 diabetes was 0.87 (95% CI 0.73–1.03) for one cup per day, 0.58 (0.49–0.68) for two to three cups per day, and 0.53 (0.41–0.68) for four or more cups per day compared with nondrinkers (P for trend <0.0001). Associations were similar for caffeinated (0.87 [0.83–0.91] for a one-cup increment per day) and decaffeinated (0.81 [0.73–0.90]) coffee and for filtered (0.86 [0.82–0.90]) and instant (0.83 [0.74–0.93]) coffee. Tea consumption was not substantially associated with risk of type 2 diabetes (0.88 [0.64–1.23] for four or more versus no cups per day; P for trend = 0.81).

CONCLUSIONS—These results suggest that moderate consumption of both caffeinated and decaffeinated coffee may lower risk of type 2 diabetes in younger and middle-aged women. Coffee constituents other than caffeine may affect the development of type 2 diabetes.

Footnotes

  • A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances.

    • Accepted October 30, 2005.
    • Received August 12, 2005.
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