Smoking and Risk on Women’s Mortality Rates

CLINICAL CONTEXT
Smoking is widely recognized as the most important modifiable risk factor in preventing adult mortality in Western countries, but there has been little attention paid overall to sex-based differences in health outcomes of smokers. Huxley and Woodward addressed this issue in a systematic review comparing cardiovascular outcomes associated with smoking among women and men. Their results, which were published in the October 8, 2011, issue of the Lancet, demonstrate that the risk for cardiovascular events associated with current smoking was more profound among women compared with men. There was no sex-based difference in the cardiovascular risk of former smokers.

Long-term data analysis on the health risks of smoking among very large groups of women has only recently been possible. The current study reports on mortality outcomes based on cigarette use in the Million Women Study.

STUDY SYNOPSIS AND PERSPECTIVE
Women who smoke lose at least 10 years from their lifespan. In particular, women who continue smoking past the age of 40 years have 10 times the hazards of those who quit smoking before that age.

Kirstin Pirie, MSc, from the Cancer Epidemiology Unit at the University of Oxford in the United Kingdom, and colleagues presented results from the Million Women Study in an article published online October 27 in the Lancet. Women were recruited for the study between the ages of 50 and 65 years and were followed up for between 9 and 15 years. The women in the study had a relatively low absolute death rate, possibly because various previous illnesses were excluded and possibly because the study included relatively healthy volunteers.

The study examined women in the United Kingdom and found that smoking accounted for two thirds of all deaths of smokers in their 50s, 60s, and 70s. Women smoking at baseline had a 12-year mortality rate of 2.76 (95% confidence interval, 2.71 - 2.81) when compared with never-smokers. For smokers younger than 70 years, the probability of death was 24% compared with 9% for never-smokers of the same age (absolute difference, 15%).

Women who stopped smoking by age 30 years avoided more than 97% of the lifetime hazard from smoking. Women who smoked until age 40 years and stopped had substantial hazards but were able to avoid more than 90% of the excess mortality caused by continuing to smoke. Women who stopped smoking at age 50 years avoided approximately two thirds the excess mortality seen in women who continue smoking at a later age. Women who quit smoking at the age of 40 years still have a mortality rate 1 to 2 times that of the never-smokers, however, and this increased mortality rate lasts for the next few decades of life.

Smokers typically experienced excess mortality from lung cancer, chronic lung disease, heart disease, and stroke, as well as other neoplastic, respiratory, or vascular conditions. For many of these diseases, the study identified a proportional excess risk in smokers that was even higher than that identified in previous studies.

The UK population was useful for studying because it includes a generation of women who smoked through adult life and reached old age. The authors seek to use the data from this study to predict the effect of smoking on female mortality outside the United Kingdom.

In a linked comment, Rachel Huxley, DPhil, from the University of Minnesota in Minneapolis and Mark Woodward, PhD, from Johns Hopkins University in Baltimore, Maryland, write, "The substantial hazards of smoking and the remarkable benefits of stopping now being seen among women in the UK emphasise the need for effective sex-specific and culturally-specific tobacco control policies that encourage adults who already smoke to quit and discourage children and young adults from starting to smoke."