Death is a certainty in life, but premature death has become less of a certainty in the United States, according to a new study. Researchers compared the rates and causes of death in the U.S. population between 1969 and 2013 using death certificate data from the National Vital Statistics System. They focused on the top killers during this period: heart disease, cancer, chronic obstructive pulmonary disease, accidents, stroke and diabetes. The researchers found that the…