Smoking causes half a million deaths each year in the U.S., killing slightly more men than women, new statistics show.

The rates of smoking-related deaths in men were comparable to what’s been found in other recent analyses. The numbers for the women, however, were higher than expected.

The study, published in the journal Epidemiology, is “an important reminder that this huge epidemic…needs ongoing measurement,” said Dr. Prabhat Jha, who studies smoking mortality and heads the Center for Global Health Research at St. Michael’s Hospital in Toronto.

“We just can’t assume that we know enough about where this epidemic is going,” Jha, who was not involved in the current study, told Reuters Health.

For the new report, Dr. Brian Rostron, then of the University of California, Berkeley, used data from a national health survey that asked nearly 250,000 people if and how much they smoked currently and in the past.

Participants were tracked for 2 to 9 years after filling out the survey. By the time the study ended, in 2006, about 17,000 of them had died.

Rostron, who now works at the Food and Drug Administration, calculated the odds of dying for smokers and non-smokers of different ages and genders.

Then he applied the extra risks due to smoking to the total U.S. population. According to his calculations, there were an average of about 290,000 smoking-related deaths in men each year between 2002 and 2006 and 230,000 in women - a total of over half a million deaths.

In all, about 2.5 million people in the U.S. die every year, according to the Centers for Disease Control and Prevention.

Among all current and former smokers, the greatest increase in risk of a tobacco-related death was seen between the ages of 65 and 74. Once other factors such as weight and alcohol consumption were taken into account, people in that age group were three times as likely to die from any cause if they currently smoked between one and two packs of cigarettes a day, compared to if they had never smoked.

As evidence of the risks of smoking has accumulated and spread, the number of current smokers in the U.S. has dropped over the past few decades.

A new study in The Journal of the American Medical Association confirms that trend: about 7 percent of adults in the U.S. were heavy smokers in 2007, compared to 23 percent in 1965. The researchers on that study, led by Dr. John Pierce of the University of California, San Diego, defined “heavy smoking” as 20 or more cigarettes a day.

Despite that good news, Jha said the new estimates show the need for more information on how smoking affects women. “It might well be that in women the effects are greater and more severe, but we need more evidence,” he said.

Jha added that while rates of smoking and deaths from smoking have been falling over the long term in the U.S., they’ve been rising in low-income countries. Because of that, “overall the number of smoking-related deaths worldwide is bound to increase,” Jha said.

Currently, there are about 5 to 6 million smoking-related deaths each year worldwide, he said.

SOURCE: Epidemiology, online March 3, 2011 and The Journal of the American Medical Association, March 16, 2011.