Adding years can result in an extended middle age—and those years can become a double-edged sword, medical experts say. Increased longevity is a huge blessing for many. But with more years, there is an increased chance to develop chronic diseases, such as heart disease, cancer and forms of dementia. The gift of more middle age years might be changing our lifespans and adding a more productive and creative period. Just don’t let it lead to an expanded waistline and an increasingly sedentary lifestyle.