Atlanta ? U.S. life expectancy has risen to a new high, now standing at nearly 78 years, the government reported Wednesday.

The increase is due mainly to falling death rates in almost all the leading causes of death. The average life expectancy for babies born in 2007 is nearly three months greater than for children born in 2006.

The new U.S. data is a preliminary report based on about 90 percent of the death certificates collected in 2007. It comes from the National Center for Health Statistics, part of the Centers for Disease Control and Prevention.

Life expectancy is the period a child born in 2007 is expected to live, assuming mortality trends stay constant. U.S. life expectancy has grown nearly one and a half years in the past decade, and is now at an all-time-high.

Last year, the CDC said U.S. life expectancy had inched above 78 years. But the CDC recently changed how it calculates life expectancy, which caused a small shrink in estimates to below 78.

The United States continues to lag behind about 30 other countries in estimated life span. Japan has the longest life expectancy: 83 years for children born in 2007, according to the World Health Organization.

Heart disease and cancer together are the cause of nearly half of U.S. fatalities. The death rate from heart disease dropped nearly 5 percent in 2007, and the cancer death rate fell nearly 2 percent, according to the report.