Life expectancy in the U.S. lags behind other prosperous nations and smoking and obesity are to blame, explains a new report from the National Research Council.

While over the last 25 years, U.S. life expectancy at age 50 has been on the rise, it's still behind such nations as Australia and Japan, despite outspending them on health care, the report explains. Concerned about the trend, the National Institute on Aging asked a global team of researchers for answers. The result is a massive report that delves into the differences and blames much of the disparities on Americans' past smoking habit and the nation's obesity epidemic.

That smoking is to blame in the states may sound odd, considering smoking bans are all the rage in the U.S. while Europe is just catching on. Well, Americans' smoking habit goes back some fifty years when smoking rates were higher here than in Europe or Japan. The consequences of that unhealthy behavior are playing out now, explains a summary of the report.

Nevertheless, the report predicts good news could be down the pike. Since major efforts to reduce smoking are underway now, life expectancy likely will improve 20 to 30 years from now. 

Rising obesity rates, however, paint a gloomier picture. Obesity alone accounts for between a fifth and a third of the shortfall in American's lifespans. And if that problem doesn't improve, it could offset the gains in life expectancy expected from people quitting smoking.