Critique 019: Both alcohol and caffeinated coffee are associated with lower risk of diabetes in African-American Women ……………… 27 September 2010

Boggs DA, Rosenberg L, Ruiz-Narvaez EA, Palmer JR.  Coffee, tea, and alcohol intake in relation to risk of type 2 diabetes in African American women.  Am J Clin Nutr 2010;92:960–966.

Authors’ Abstract

Background: Numerous studies have reported inverse associations of coffee, tea, and alcohol intake with risk of type 2 diabetes, but none has reported results separately among African American women.

Objective: We prospectively examined the relation of coffee, tea, and alcohol consumption to diabetes risk in African American women.

Design: The study included 46,906 Black Women’s Health Study participants aged 30–69 y at baseline in 1995.  Dietary intake was assessed in 1995 and 2001 by using a validated food-frequency questionnaire.  During 12 y of follow up, there were 3,671 incident cases of type 2 diabetes.  Relative risks (RRs) and 95% CIs were estimated by using Cox proportional hazards models adjusted for diabetes risk factors.

Results: Multivariable RRs for intakes of 0–1, 1, 2–3, and ≥4 cups of caffeinated coffee/d relative to no coffee intake were 0.94 (95% CI: 0.86, 1.04), 0.90 (95% CI: 0.81, 1.01), 0.82 (95% CI: 0.72, 0.93), and 0.83 (95% CI: 0.69, 1.01), respectively (P for trend = 0.003).  Multivariable RRs for intakes of 1–3, 4–6, 7–13, and ≥14 alcoholic drinks/wk relative to never consumption were 0.90 (95% CI: 0.82, 1.00), 0.68 (95% CI: 0.57, 0.81), 0.78 (95% CI: 0.63, 0.96), and 0.72 (95% CI: 0.53, 0.98), respectively (P for trend , 0.0001).  Intakes of decaffeinated coffee and tea were not associated with risk of diabetes.

Conclusion: Our results suggest that African American women who drink moderate amounts of caffeinated coffee or alcohol have a reduced risk of type 2 diabetes.

Forum Comments

While a rather striking inverse association between moderate drinking and the risk of developing diabetes mellitus (DM) has been shown in most epidemiologic studies of the general population1-3, specific associations among large cohorts of African-Americans have not been reported.  This could be important since African-Americans, especially women, tend to drink little alcohol yet are at markedly increased risk of DM. 

Further, some studies have shown less effect of moderate drinking on the risk of cardiovascular disease and mortality among African-Americans than seen among other ethnic groups.  Klatsky et al4, using data from the Kaiser Permanente Study, found similar J-shaped curves for the association between alcohol and heart failure for whites, Asians, and African-Americans.  On the other hand, Freiberg et al5, using data from the large Women’s Health Initiative, showed that all white women and African-American women who were hypertensive had the expected J-shaped curve, but the non-hypertensive African-American women did not show lower mortality to be associated with moderate alcohol consumption5.

This study of a very large number of subjects shows very similar results (a lower risk of DM) for moderately drinking African-American women as have been shown among whites.  The risk of DM for consumers of 4-6 drinks/week was about 30% lower than that of non-drinkers, a lower risk that is very similar to what has been shown in previous meta-analyses based primarily on other ethnic groups.  It would be interesting to see a more detailed analysis of other dietary habits (e.g. consumption of vegetables, fruit, nuts, unsaturated versus saturated fats as an index of less meat and dairy consumption, etc.), which could be confounding the apparently clear conclusion that a daily alcoholic drink reduces risk of diabetes.  Further, as with all observational studies, there is always the risk of the results being affected by unknown confounders, although this study seems particularly thorough in adjusting for such.

Obesity is a key factor in the development of adult-onset DM.  It is interesting that this paper shows almost identical reductions in the risk of DM for subjects consuming ≥ 4 drinks/week whether they had a BMI < 25 kg/m2, 25-29 kg/ m2, or ≥ 30 kg/ m2.  This is unlike the Nurses’ Health Study6 in which a strong inverse association between alcohol drinking and body weight explained much of the apparent protective effect of alcohol.  In that study, however, even after adjustment for Quetelet index [weight (kg)/height (m)2], family history of diabetes, total caloric intake, and age, the relative risk of diabetes for consumers of 15+ g per day was 0.6 (95% CI 0.3-0.9) in comparison with that of non-drinkers6.

The study also supports previous studies showing an inverse association between caffeinated coffee intake and DM.  (As one Forum member commented, it appears we are describing Irish coffee.)  The study found no association between decaffeinated coffee or tea and the risk of DM.

Summary:  In a very large cohort of African-American women in the US, the association between the consumption of alcohol, tea, and coffee was related to the development of type 2 diabetes mellitus over a follow-up period averaging 12 years.  Tea and decaffeinated coffee showed no relation with diabetes, but the intake of both caffeinated coffee and alcohol showed a significant inverse association. 

This paper is particularly important because some previous studies have not shown a strong association between alcohol and the risk of cardiovascular disease among African-Americans.  African-Americans, especially women, tend to drink little alcohol, yet are at markedly increased risk of diabetes.  In the present study, the approximately 30% lower risk for moderate alcohol drinkers was about the same in these African-American women as has been found in many previous studies of whites.

References from Forum Review

1.  Koppes LL, Dekker JM, Hendriks HF, et al. Moderate alcohol consumption lowers the risk of type 2 diabetes: a meta-analysis of prospective observational studies. Diabetes Care 2005;28:719–725.

2.  Carlsson S, Hammar N, Grill V. Alcohol consumption and type 2 diabetes.  Meta-analysis of epidemiological studies indicates a U-shaped relationship. Diabetologia 2005;48:1051–1054.

3.  Baliunas DO, Taylor BJ, Irving H, et al. Alcohol as a risk factor for type 2 diabetes: a systematic review and meta-analysis. Diabetes Care 2009;32:2123–2132.

4.  Klatsky et al, Alcohol drinking and risk of hospitalization for heart failure with and without associated coronary artery disease.  Am J Cardiol 2005;96:346-351.

5Freiberg MS, Chang Y-F, Kraemer KL, Robinson JG, Adams-Campbell LL, Kuller LL.  Alcohol consumption, hypertension, and total mortality among women.   Am J Hypertens 2009; 22:1212-1218.

6.  Stampfer MJ, et al.  A prospective study of moderate alcohol drinking and risk of diabetes in women.  Am J Epidemiol 1988;128:549-558.

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Comments included in this critique by the International Scientific Forum on Alcohol Research were provided by the following:

Erik Skovenborg, MD, Scandinavian Medical Alcohol Board, Practitioner, Aarhus, Denmark

Ross McCormick PhD, MSC, MBChB, Associate Dean, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand

Harvey Finkel, MD, Hematology/Oncology, Boston University Medical Center, Boston, MA, USA

R. Curtis Ellison, MD, Section of Preventive Medicine & Epidemiology, Boston University School of Medicine, Boston, MA, USA

Roger Corder, PhD, MRPharmS, William Harvey Research Institute, Queen Mary University of London, UK