For the first time since the 1918 Spanish flu pandemic, life expectancy for a significant proportion of the United States is on the decline largely because of an increase in chronic diseases related to obesity, smoking and high blood pressure.

Although life expectancy for all other Western nations and for most of the U.S. has continued to improve over the past several decades, researchers at Harvard University and the University of Washington say many of the worst-off here are getting much worse.

One of every five American women, and one of every 25 men, are either dying at a younger age or seeing no improvement in life span. Although this deadly trend is mostly centered in the southern parts of the nation, several largely rural counties in Washington -- Cowlitz, Lewis, Benton and Grays Harbor -- are also on the verge of seeing a decline in overall life span.