Stroke fell from the third leading cause of death in the U.S. for the first time in 50 years. (Pablo Martinez Monsivais/Associated Press)

American life expectancy has fallen slightly after years of increases.

A baby born in 2008 could expect to live 77.8 years, down from a high of 77.9 years the year before, according to preliminary data published by the U.S. Centers for Disease Control and Prevention in Atlanta.

The change of about a month is "minuscule," said the report's lead author, Arialdi Minino of the CDC's National Center for Health Statistics.

The cause of the slight decline in overall life expectancy is unclear.

"It's something to keep our eyes on," said Ken Thorpe, a health policy professor at Emory University in Atlanta, who suggested it could be related to rising obesity rates.

In comparison, Statistics Canada reported in February that a Canadian's life expectancy at birth reached 80.7 years during the three-year period from 2005 through 2007.

Overall, American women were expected to live 80.3 years and men 75.3 years, according to the latest data.

The preliminary infant mortality rate for 2008 was 6.59 deaths per 1,000 live births, a 2.4 per cent decline from the 2007 rate of 6.77 and an all-time low, the CDC said.

Canada's infant mortality rate was 5.1 per 1,000 live births in 2007, according to Statistics Canada.

The CDC report showed that stroke fell from the third leading cause of death in the U.S. for the first time in 50 years. It moved behind chronic lower respiratory diseases, which include asthma, emphysema and chronic bronchitis. These ailments increased, although they were counted differently in the latest report.

Dr. Ralph Sacco, president of the American Heart Association, said the group was "heartened to see a continuing decrease in stroke mortality."

Sacco attributed the drop to better prevention, increased use of clot-busting drugs in stroke patients, and medications to prevent strokes.

Other highlights of the report included:

• Death rates fell for six of the 15 top causes of death in the U.S. — heart disease, cancer, stroke, diabetes, homicide and accidents.
• Deaths from Alzheimer's, flu and pneumonia, high blood pressure, suicide and kidney disease all rose in 2008.
• Heart disease and cancer, the two leading causes of death, still accounted for nearly half (48 per cent) of all deaths in 2008.

The report was based on death certificates reported to the agency.

With files from The Associated Press