Women who smoke are 25 percent more likely than their male counterparts to develop heart disease, and the risk increases the longer women maintain the habit, according to research published Thursday in the Lancet medical journal.
The higher risk could be because the toxins in cigarettes have a more potent effect on women than they do on men, researchers from the University of Minnesota and Johns Hopkins University wrote after surveying data from 4 million people in 86 studies spanning 45 years.
Women account for one in five of the world's 1.1 billion smokers and almost one in three tobacco-related deaths, the authors wrote.
Women also are taking up smoking faster than men in some developing nations where smoking has traditionally been a male habit, according to the World Health Organization.
"What makes the realization that women are at increased risk worrisome is that the tobacco industry views women as its growth market," Matthew Steliga, a thoracic surgeon at the University of Arkansas for Medical Sciences, and Carolyn Dresler, director of Arkansas' Tobacco Prevention and Cessation Program, wrote in an editorial accompanying the study.
Previous studies have produced conflicting evidence about whether there is a difference in heart-disease risk between men and women who smoke, the researchers said.
Rachel Huxley, from the University of Minnesota, and Mark Woodward, from Johns Hopkins, scoured four online databases for studies about smoking and heart disease published between 1966 and 2010.
From an initial list of 8,005 articles, they found 26 that contained information from 86 studies involving 3.9 million people around the world.
Compared with nonsmokers, women who light up have a 25 percent greater chance of coronary heart disease than male smokers, independent of other risk factors, the authors found.
The risk increases 2 percent every year they continue smoking, they wrote.
While male smokers consume more cigarettes on average than women, female smokers may extract more carcinogens and other poisons from cigarettes than men, the researchers said.
That may also explain why female smokers have twice the risk of developing lung cancer, they said.
"Cigarette smoking is one of the main causes of coronary heart disease worldwide and will remain so as populations that have so far been relatively unscathed by the smoking epidemic begin to smoke to a degree previously noted only in high-income countries," Huxley and Woodward said in an emailed statement.
"This expectation is especially true for young women with whom the popularity of smoking, particularly in some low-income and middle-income countries, might be on the rise."