Testosterone treatment appears to improve the underlying problem in some men with type 2 diabetes, according to a study funded by U.K. drugmaker ProStrakan.

The problem — called "insulin resistance" — is that the body doesn't know how to use insulin to process sugar. Researchers found that applying testosterone in a gel reduced this problem in diabetic men who had low levels of testosterone to begin with, or in similar men without diabetes but with a cluster of heart disease risk factors called metabolic syndrome.

It also lowered their cholesterol levels and had some impact on their sexual function, as compared with a gel that looked the same but had no testosterone in it.

Writing in the journal Diabetes Care, Dr. T. Hugh Jones of Barnsley Hospital in the U.K. and colleagues say their findings support testosterone treatment in men with low testosterone and type 2 diabetes or metabolic syndrome.

In the new study, the researchers tested ProStrakan's testosterone gel Tostran against a dummy gel in 220 middle-aged and older men. The men used the gel once a day for a year.

The insulin resistance went down by 16 percent in men on Tostran, despite the fact that many were already taking metformin, a drug that helps control blood sugar levels.

Still, there was no difference overall between the fake gel and testosterone in terms of blood sugar control, the ultimate goal in diabetes care.

The researchers also found the general sexual function improved slightly with the testosterone gel, but there was no difference in erectile dysfunction or overall sexual satisfaction.

The side effects were similar between the dummy gel and Tostran, although testosterone may sometimes cause swelling around the joints and in the breasts.

Testosterone is already used to treat sexual problems in men whose levels of the hormone are lower than normal. The gels can cost more than $250 per month, and experts disagree about how low testosterone levels in the body should drop before they prescribe treatment.

With millions of prescriptions every year in the U.S., some experts believe it's being overused.
"We need a lot less testosterone for sexual function than people used to think," Dr. Michael Marberger, who heads the urology department at the University of Vienna Medical School in Austria, told Reuters Health last year. "Obesity impacts sexual function much more."