If you're sedentary or overweight, you tend to develop type 2 diabetes at an earlier age than you would if you exercised and lost weight. Gerald Bernstein, MD, is an endocrinologist with a family history of the disease. He knew that exercise can help delay the onset of diabetes and started running in his mid-40s. He wasn't diagnosed until he was 65; many of his family members were diagnosed in their 40s.