Major Finding: Women who drank more than 4 cups of coffee daily were 56% less likely to develop type 2 diabetes than were those who drank no coffee, a significant difference. After adjustment for SHBG, the difference was not significant.
Data Source: Nested case-control study of 359 women with incident type 2 diabetes and matched controls from the Women's Health Study.
Disclosures: Study supported by a grant from the National Institutes of Health.
SAN FRANCISCO — Sex hormone–binding globulin may be the key to the protective effect of coffee consumption against development of type 2 diabetes, according to an analysis of the Women's Health Study.
Women who drank at least 4 cups of coffee per day were less than half as likely to develop diabetes than were those who drank no coffee, and after adjustment for sex hormone–binding globulin (SHBG), the interaction disappeared.
It has been known for some time that women who drink coffee are significantly less likely to develop type 2 diabetes than are those who do not, and that the relationship between coffee consumption and diabetes is much less pronounced in men.
SHBG is a glycoprotein with a high affinity for testosterone and estradiol. SHBG levels tend to be substantially higher in women than in men, Atsushi Goto, a doctoral candidate at the University of California, Los Angeles, said at a conference sponsored by the American Heart Association. Previous studies have shown that variations in the genes controlling SHBG have a strong association with the development of diabetes and that coffee consumption increases plasma levels of SHBG.
To study this association, Mr. Goto and his colleagues used data from the Women's Health Study, in which nearly 40,000 women were followed for a median of 10 years. During that time, 359 of the women developed diabetes. The investigators matched those women by age, race, and time of blood draw with 359 women who had not developed the disease.
After adjustment for age, smoking, alcohol consumption, physical activity, past use of hormone therapy, total energy intake, fiber intake, body mass index, and plasma testosterone and estradiol levels, the investigators found that women who drank at least 4 cups of caffeinated coffee (500 mg caffeine) daily had significantly higher mean SHBG levels than did nondrinkers: 27.3 nmol/L versus 24.5 nmol/L. Decaffeinated coffee was not significantly associated with SHBG levels.
Furthermore, when controlling for all of the above factors plus education levels and family history of type 2 diabetes, the investigators found that women who drank at least 4 cups of caffeinated coffee daily were 56% less likely to develop diabetes than were nondrinkers. However, when the investigators additionally controlled for plasma SHBG levels, the decrease in risk associated with coffee consumption became nonsignificant. This suggests that it is SHBG that mediates the decrease in risk of developing type 2 diabetes, Mr. Goto commented.