CNN  —  Consider three hypothetical women in their mid-70s, all living alone in identical economic circumstances with the same array of ailments: diabetes, arthritis and high blood pressure. Ms. Green stays home most of the time and sometimes goes a week without seeing people. But she’s in frequent touch by phone with friends and relatives, and she takes a virtual class with a discussion group from a nearby college. Ms. Smith also stays home but rarely talks to anyone. She has lost contact with friends, stopped going to church and spends most of her time watching TV. Ms. Johnson has a wide circle of friends and a busy schedule. She…