The study sample included 1,413 adult men aged 20 years and older, who participated in the morning session of the first phase of the Third National Health and Nutrition Examination Survey (NHANES, a cross-sectional survey of the civilian, non-institutionalized population of the U.S). 

Bio-available and free testosterone levels were calculated from serum total testosterone, sex hormone-binding globulin, and albumin concentrations. 


In multivariable models adjusted for age, race/ethnicity, and adiposity, men with the lowest free testosterone levels (below 9 ng/dl) were over 4 times more likely to have prevalent diabetes compared with men in the highest free testosterone levels (over 14 ng/dl). 

Similarly, men in the lowest levels of bio-available testosterone (below 211 ng/dl) also were close to 4 times as likely to have prevalent diabetes compared with men with the highest (over 302 ng/dl). 

These associations persisted even after excluding men with clinically abnormal testosterone levels defined as total testosterone below 325 ng/dl or free testosterone below 7 ng/dl. 

No clear association was observed for total testosterone after multivariable adjustment. However, a trend was seen for which men with total testosterone levels below 454 ng/dl were 27% more likely to have prevalent diabetes as compared to me with total testosterone levels over 627 ng/dl). 


Low free and bio-available testosterone concentrations in the normal range are associated with diabetes, independently of adiposity. These data suggest that low androgen levels may be a risk factor for diabetes in men. 

Associations of low free and bio-available testosterone levels with diabetes remained even after adjustment for age and known confounding factors like race/ethnicity and adiposity (measured by BMI and waist-to-hip ratio). The association with low free testosterone persisted even after the exclusion of men with clinically low total and/or free testosterone levels, suggesting that this association was not driven by men who exhibit excessively low testosterone levels (ie. hypogonadal men). 

The take home message from this study is that having testosterone levels in the low end of the normal range, even above the threshold for diagnosis of testosterone deficiency, can significantly contribute to the development of insulin resistance and diabetes. 



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