Women who smoke have a 25% higher risk of heart disease than men who smoke, and the longer they smoke, the bigger this risk becomes relative to men who smoke for the same number of years, according to a new pooled data study published today, 11 August in The Lancet. The researchers suggest physiological differences between the sexes, or perhaps because women smoke differently to men, means women are more strongly affected by the cancer-causing chemicals in tobacco smoke.

The British Heart Foundation said they found the study’s results “alarming”, especially as women tend to smoke fewer cigarettes than men, reports BBC News.

Dr Rachel R. Huxley, of the division of epidemiology at the University of Minnesota, and Dr Mark Woodward, of Johns Hopkins University in Maryland, both in the US, conducted a systematic review and meta-analysis of prospective cohort studies.

They reviewed studies that measured smoking and heart risk in men and women published between between 1966 and 2010 and found 75 data sets covering 2.4 million participants where researchers had done three things that met their criteria: (1) they had measured Relative Risk (RR) of coronary heart disease for men and women separately, (2) examined how it varied with current smoking compared with not smoking, and (3) adjusted for cardiovascular risk factors other than coronary heart disease.

When they analyzed the pooled data, Huxley and Woodward adjusted the figures to eliminate, as far as possible, the effect of sex differences in other major risk factors.

They expressed their results in RRRs: Relative Risk Ratios. The Relative Risk bit is the risk of a smoker developing heart disease, compared to a non-smoker. Then, by comparing results for men and women, they calculated ratios to express how the relative risk of being a smoker varies between the sexes.

Note that they did not take into account the number of cigarettes that men and women smoked, they just examined the risk of being a smoker relative to being a non-smoker.

They found that:

  • The pooled, adjusted RRR of smoking compared with not smoking for coronary heart disease was 1.25 (95% CI ranged from 1·12 to 1·39, p

The researchers also found data in 53 studies that had compared previous smokers with never smokers. When they pooled data from these, they found no evidence of a difference between men and women, comparing the relative risk of previous smokers with never smokers (RRR 0·96, 95% CI 0·86 to 1·08, p=0·53).

They concluded that it was not clear whether these differences in risk of coronary heart disease between men and women smokers are due to biology or differences in smoking behaviour.

“Tobacco-control programmes should consider women, particularly in those countries where smoking among young women is increasing in prevalence,” they urged.

Written by Catharine Paddock PhD