April 19 (Bloomberg) -- The U.S. death rate for 2004 fell to the lowest level ever recorded, and life expectancy at birth rose to a new high, federal officials said.

The death rate, adjusted for the changing age distribution of the population, fell 3.8 percent to 801 per 100,000 in 2004, led by declines in heart disease mortality, according to the National Center for Health Statistics, based in Hyattsville, Maryland. Life expectancy at birth rose to a record 77.9 years from 77.5, researchers said in a report released today.

The agency didn't cite reasons for the changes. ``We really don't know -- we can't pin it down,'' said Arialdi Minino, a 41- year-old statistician and lead author of the report, in a telephone interview.

The age-adjusted mortality rate for heart disease, the leading cause of death, fell 6.4 percent to 217.5 in 2004, the agency said. While the heart disease rate goes a long way toward explaining the total figures, Minino said, he doesn't know why mortality from heart disease is declining.

``Year-to-year variations need to be treated with caution,'' said Wayne Rosamond, a professor of epidemiology at the University of North Carolina in Chapel Hill, in a telephone interview. U.S. mortality from heart disease has been falling from a peak in 1968, he said.

``The decline reflects a combination of treating people better and preventing the disease from happening in the first place,'' said Rosamond, 48, who also heads the statistics committee of the Dallas-based American Heart Association, a research and advocacy group.

Prevention

Prophylactic measures such as weight loss, cessation of smoking and blood-pressure control through drugs may account for half the drop in mortality, Rosamond said.

Definitive national studies don't exist on how many people get heart disease, he said.

People of both sexes, and from all racial and ethnic groups tracked by researchers, had lower death rates, according to the report. Heart disease remained the leading cause of death, followed by cancer, stroke, chronic lower-respiratory disease, accidents and diabetes, the researchers said.

The 15 leading causes of death were the same in 2004 as in 2003, except that Alzheimer's disease became No. 7, passing the category comprising influenza and pneumonia.

The gap in life expectancy between whites and blacks closed a bit, as did the gulf between women and men, according to the report. After the narrowing, the life span was 5.2 years higher for females than for males, the smallest such difference since 1946. Life expectancy was 5 years higher for whites than for blacks.

The report was based on about 90 percent of death records for 2004, covering 2.4 million deaths. The data were collected from the 50 states, plus the District of Columbia, while excluding Puerto Rico and other U.S. territories.

To contact the reporter on this story: Jeffrey Tannenbaum in New York at jtannenbaum@bloomberg.net.

Last Updated: April 19, 2006 17:41 EDT