I think the facts have been out for a while. Those of us with very low T, are, quite simply, unable to keep ourselves fit and healthy without medical intervention.
As an example, Diabetes and blood sugar control are certainly affected by testosterone levels. With higher T being better. I don't want to say T replacement is a magic bullet, it's not. But coupled with exercise and good diet, it's an effective way to get into better physical condition and that results in better health.