Until fairly recently, low testosterone in men (I call it "low T") was treated only in patients with severe and obvious T deficiencies, such as men with congenital hormonal conditions that affected their pituitary gland or those who had lost both testicles to trauma, tumors, or infections.  However, as the medical community has learned more about the benefits of T therapy for men with less obvious causes of low T (e.g., improved sexual desire and function, energy, and body composition), there has been concomitant interest in how T relates to other medical conditions, including diabetes.  It turns out that the relationship between low T and diabetes is quite involved, although the final chapter on the ultimate nature of the relationship is still to be written.  

One key observation is that there is a very high prevalence of low T among men with diabetes.  In a study (the HIM study: Hypogonadism in Males) of approximately 300 general medical offices, patients were asked to provide their entire medical history and then underwent a blood test for testosterone.   The fraction of men with T concentrations less than the FDA's threshold for normal T levels (i.e., less than 300 ng/dl) was greatly increased in men with certain medical conditions compared with men without those conditions.  Approximately 50 percent of men with diabetes had low T, and the overall risk of low T in this population was more than double the risk seen in men without diabetes. 

OK- so this study (and others with similar results) suggests that men with diabetes are at higher risk of having low T. So what?  Well, the story gets more interesting.  There is a very sophisticated type of study, called a longitudinal study, in which individuals give a blood sample which is then frozen, and these individuals are subsequently followed for many years.  At the end of the study, the researchers can test the frozen blood samples to determine whether hormone levels like testosterone, for example, predicted the development of medical conditions such as diabetes.  It turns out that men with the lowest 25 percent of T concentrations in the study population were at increased risk of developing diabetes.  In other words, having a relatively low concentration of T in the blood increased the probability of being diagnosed with diabetes sometime later.  The risk was also increased for development of metabolic syndrome, a group of conditions (including diabetes) that predicts subsequent risk of heart attack and stroke. 

The final (so far) piece to this story is that treatment of low T with T therapy appears to improve the body's ability to handle glucose and its partner, insulin.  Because this has been shown in some studies, but not in others, at this point we can say only that the data suggest that normal T is helpful for diabetes control.  A related fact, though, is that T therapy increases muscle mass and lowers body fat, and both of these changes are helpful with blood sugar control.  This piece of the puzzle supports the idea that normalizing T may be helpful for diabetes. 

What's the bottom line, then, regarding T and diabetes?  The practical issue is that men with diabetes are at high risk of already having low T and should therefore be checked for it.  Certainly, if diabetic men have symptoms of low sex drive, weak erections, chronic fatigue, depressed mood, or osteoporosis, they should ask their primary care physician, endocrinologist, or urologist (if they have one) to obtain blood tests for total and free testosterone (the portion that is bioavailable).  If either one is low, then consideration should be given to beginning T therapy.   

Testosterone therapy comes in several forms.  The most common treatment in the United States is a gel applied daily to the skin of the upper arms and shoulders.  Other forms of treatment are skin patches, intramuscular injections, and implantable pellets.     

Given the intriguing and suggestive evidence regarding the relationship of testosterone and blood sugar control, it will be interesting to learn from larger, prospective studies whether one day T therapy may become indicated even in asymptomatic men for overall health and possibly for warding off the risk of future development of diabetes.   

Abraham Morgentaler, MD, is an associate clinical professor of urology at Harvard Medical School and the founder of Men's Health Boston (www.MensHealthBoston.com), a center focusing on sexual and reproductive health for men. Dr. Morgentaler's newest book, Testosterone for Life (McGraw-Hill), is the first consumer book about low T by a specialist in the field, and it explains every aspect of this common medical condition and its treatment.