Life expectancy is rising in much of the world. But doctors are seeing another trend that is disturbing. Some people are choosing lifestyles that result in early death. A new US study looks at four lifestyle choices that prevent people from staying healthy and living longer. It used to be rare for people to live to 100. But babies born in the US today can hope to live that long. In the 20th century, life expectancy in wealthy nations increased by as much as 30 years. Average life expectancy for Americans is 78. But doctors are seeing people adopt bad habits that can cut their life short, such as eating too much or eating too much junk food, exercising too little and smoking cigarettes. These habits increase the risk for cancer, heart disease and stroke. Researchers at Harvard University and the University of Washington wanted to find out how many years are lost with these lifestyle choices. "What we found was that high blood pressure, smoking, overweight account for five years of loss of life expectancy in men and about four years in women at the national level," Goodarz Danaei, one of the principal researchers said. The researchers broke down the data into race, income and location, and they found even greater differences. Middle-income whites have the best blood pressure. But Asian-Americans have fewer bad habits and the best health. "They are not getting heart disease because of low blood pressure. They are not getting cancer because they have low risk factors for cancer, including smoking," Danaei said.