A study from the American Cancer Society reveals improved treatments for chronic illnesses like heart disease and cancer have resulted in a drop in the U.S. death rate since 1970. But Americans today face increasing threats from obesity and smoking.

An analysis of annual U.S. mortality rates found deaths from all causes declined 32 percent from 1,242 deaths per 100,000 in 1970 to 845 per 100,000 people in 2002.

The study also took a look at the six leading causes of death and their mortality rates over three decades. Rates declined 63 percent for strokes, 52 percent for heart disease, 41 percent for accidents and 3 percent for cancer. The death rate from chronic lung disease, however, doubled, rising 45 percent from diabetes.

According to study author Ahmedin Jemal of the American Cancer Society, "While improved detection and treatment for chronic diseases has resulted in declining mortality rates, it has also increased the prevalence of 'treated disease' and an associated increase in health care expenditures."

The report is published in this week's issue of the Journal of the American Medical Association.