Studies like the one by Dandona and colleagues from USA (2010) have found that there may be a correlation between low testosterone levels in men and type 2 diabetes. Other studies like the one by Boyanov and colleagues from Bulgaria (2003) and by Lee and colleagues from China (2005) have found that testosterone supplementation may improve insulin sensitivity and blood sugar control if the diabetics have low testosterone levels. An analysis by Ginsburg and colleagues from USA found low incidence (%) of adverse effects of testosterone supplementation over long term. So it may be useful for you as a diabetic to take testosterone supplements if you know that you have low testosterone levels. However, testosterone is a hormone and should be taken carefully after consultation with your doctor.