If you're a man over 40 with low testosterone and you take testosterone therapy, your erectile function will improve no matter how old you are, how much you weigh, if you have diabetes, or how low your testosterone was to start — but if you're older or heavier, your overall function might still be lower than someone younger or leaner.

In men 75 and older, having more testosterone in the blood is linked to a lower chance of having metabolic syndrome — for every little boost of 10 ng/dL in testosterone, their risk drops by about 3%, no matter how much they sleep, exercise, or eat.

In older men, having low testosterone seems to go hand-in-hand with more heart disease, but that’s probably because low testosterone often comes with other issues like being overweight, having high blood sugar, or inflammation — so it’s not necessarily testosterone itself causing the problem.

In older men, having less testosterone seems to go hand-in-hand with having a bigger waist, higher blood sugar, more body inflammation, and lower 'good' cholesterol — all signs of metabolic syndrome — but this doesn’t happen the same way in older women.

For men over 40 with low testosterone, taking testosterone supplements may help improve their sexual function enough to make a real difference in how they feel, compared to not taking anything.

In older men, low testosterone doesn’t seem to directly cause metabolic syndrome—instead, it’s mostly because they tend to have more body fat, insulin problems, inflammation, and bad cholesterol, which are the real culprits.