The authors, led by Rachel Huxley of the University of Minnesota, reviewed studies published between 1966 and 2010 on 2.4 million people, including 44,000 cardiac events.

They found female smokers to have a 25 percent greater risk for coronary heart disease then male smokers -- and the difference in risk for male and female smokers increased by 2 percent for each year they smoke.

 

"Prevalence of smoking is increasing in women in some populations and is a risk factor for coronary heart disease," wrote Huxley and her colleagues in The Lancet.

 

"Whether mechanisms underlying the sex difference in risk of coronary heart disease are biological or related to differences in smoking behaviour between men and women is unclear. Tobacco control programmes should consider women, particularly in those countries where smoking among young women is increasing."

 

A fifth of the world's 1.1 billion smokers are women, and an analysis released in March said millions of women in developing countries risked disease and death as their rising economic and political status leads them to smoke more.

 

"It hasn't been widely recognized that there had been this sex difference," Huxley said. "For example, there are some data that indicate women will absorb more of the harmful agents in cigarettes compared to men. Women may inhale more smoke or they may smoke more intensively."