For those common diseases, such as skin disease, impotence, diabetes, or senile dementia, many people do not care much. "When you are old, those seemingly minor diseases may cost your life because your body's ability to resist these diseases will be lower," said Dr. Kane. He is a world-renowned expert in physical health and safety management at the Vanderbilt University Law School. Here is a list of diseases that you need to pay most attention to (from 1-star to 5-star). They are your health's biggest killers.