Smoking is more likely to give women heart disease than men, a study has found.

Toxic chemicals in tobacco smoke may have a more potent effect on women due to biological differences, scientists believe.

US researchers analysed pooled data on around 4 million individuals from 86 studies. After adjusting for other risk factors, they found the increased risk of heart disease linked to smoking was 25% higher for women.

The longer a woman smoked, the greater her heart disease risk was compared with that of a man who had smoked for the same length of time. A woman's extra risk increased by 2% for every additional year she had been smoking.

The findings are published on Thursday in an online edition of The Lancet medical journal.

Authors Dr Rachel Huxley, from the University of Minnesota, and Dr Mark Woodward, from Johns Hopkins University, of Maryland, wrote: "Women might extract a greater quantity of carcinogens and other toxic agents from the same number of cigarettes than men.

"This occurrence could explain why women who smoke have double the risk of lung cancer compared with their male counterparts.

"Physicians and health professionals should be encouraged to increase their efforts at promotion of smoking cessation in all individuals.

"Present trends in female smoking, and this report, suggest that inclusion of a female perspective in tobacco-control policies is crucial."

In the UK, 21% of women and 22% of men smoke cigarettes.

Ellen Mason, senior cardiac nurse at the British Heart Foundation, said: "It's alarming to see such a large study confirm that women are so much more at risk of heart disease from smoking than men.

"Despite women generally smoking fewer cigarettes a day than men, women appear to be substantially more at risk of getting heart disease. Biologically, women seem more susceptible to the dangers of smoking and passive smoking.

"There is free support widely available on the NHS to help both men and women quit but more effort needs to be made to encourage women not to smoke in the first place – particularly the many young women who take up this addictive and harmful habit every day.

"This is very timely research as tobacco companies are increasingly targeting women with slim brands and slick packaging."