Men with low levels of testosterone could be at greater risk of developing diabetes, a study has suggested.
Researchers from the University of Edinburgh 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.
But scientists said the study provides evidence of increased risk ‘even when body mass is not affected’.
Dr Kerry McInnes, from the university’s endocrinology unit, said: ‘We know that men with low testosterone levels are more likely to become obese and as a result, develop diabetes.
‘This study shows that 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.’
The research team said the study is the first to directly show how low testosterone levels in fat tissue can be ‘instrumental’ in the onset of the condition.
They said the findings show that mice with impaired testosterone function in fat tissue were more likely to be insulin-resistant. However, they also reveal that insulin resistance occurs 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 are higher in mice with decreased testosterone.
Now, the team hopes its 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, shows that mice without androgen receptors in fat tissue to which testosterone can attach were more likely to show signs of insulin resistance than other mice.
The researchers said mice without androgen receptors also become fatter than other mice and develop full insulin resistance when fed a high-fat diet.
Dr Iain Frame, director of research at Diabetes UK, said: ‘We already know that low testosterone levels are associated with increased obesity and therefore with increased risk of developing type 2 diabetes, but this study provides evidence that there can be increased risk even when body mass is not affected.
‘Yet while testosterone-impaired mice developed insulin resistance whatever diet they were given, the effect was considerably more pronounced on those fed on a high-fat diet. This reinforces Diabetes UK advice that a healthy balanced diet is important for everyone and particularly for those already at high risk of developing type 2 diabetes.’
He added that further work is needed to translate the findings into clinical practice, as results in mice may not necessarily have direct relevance for humans.