MEN with low levels of testosterone could be at greater risk of developing diabetes than first thought.

Researchers from Edinburgh University found low testosterone levels are linked to a resistance to insulin, the hormone that controls blood sugar levels.

Testosterone is present throughout the body and low levels are associated with increased obesity, a known risk factor for developing type 2 diabetes. However, scientists said the study provided evidence of increased risk "even when body mass is not affected".

Dr Kerry McInnes, from the university's endocrinology unit, said: "We know men with low testosterone levels are more likely to become obese and as a result, develop diabetes.

"This study shows low testosterone is a risk factor for diabetes no matter how much a person weighs. As men age their testosterone levels lower. This, along with increasing obesity, will increase the incidence of diabetes."

A total of 237,468 people in Scotland were diagnosed with diabetes in 2011, according to the latest official figures. Some 56% of them were men, who were also more likely than women to develop type 2 diabetes.

The research team said the study was the first to directly show how low testosterone levels in fat tissue could be "instrumental" in the onset of the condition. They said the findings showed that mice with impaired testosterone function in fat tissue were more likely to be insulin-resistant.

However, they also revealed insulin resistance occurred in mice when testosterone function was impaired regardless of body weight.

Researchers said the findings could help explain why older men are more at risk of developing diabetes because testosterone levels fall in men as they age.

The scientists believe a protein called RBP4 plays a crucial role in regulating insulin resistance when testosterone is impaired. They found levels of the protein were higher in mice with decreased testosterone.

Now, the team hopes the findings could lead to treatments that regulate production of RBP4 and reduce the risk of diabetes in men with less testosterone.

Researchers are planning to study patients with type 2 diabetes to see if their levels of testosterone correlate with levels of RBP4.

Testosterone acts on fat cells through molecules known as androgen receptors. These enable the hormone to activate genes which are linked to obesity and diabetes.

The study, funded by Diabetes UK, showed mice without androgen receptors in fat tissue, to which testosterone can attach, were more likely to show signs of insulin resistance.