Exercise seems to help the body manage glucose, so doctors routinely tell everyone at risk of diabetes to get more exercise.
Exercise causes the cells to release oxidants, which do lots of molecular damage and may (or may not) be one of the main causes of aging.
So maybe the way to get the best outcome would be to exercise more but also take lots of anti-oxidants, like Vitamin C and E, to curb the damage caused by oxidants.
Alas, a new study seems to show that if you take lots of anti-oxidants, exercise no longer has any effect on your body's ability to handle glucose. The potentially harmful release of oxidants seems to be key to the healthful effects of exercise on diabetes.
Whenever I read that this or that (anti-oxidants, say) is the key to health, I roll my eyes, because our bodies are machines of a complexity far beyond anything we can really understand. Tinkering with one system may cause a whole cascade of changes to others. Better, I think, just to focus on the things we understand from millennia of experience: that an active life, a moderate diet, and a positive attitude all correlate with health and long life.