Byline: Bloomberg

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 in The Lancet 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 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's Tobacco Prevention and Cessation Program, wrote in an editorial accompanying the study.

Previous studies have produced conflicting evidence about whether there's 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. …