SAN DIEGO — Women are more susceptible to the lung-damaging effects of smoking, compared with men, results from a large case-control study demonstrated.
The gender effect seemed to be most pronounced when the level of smoking exposure was low and decreased in magnitude with an increasing number of pack-years, lead investigator Dr. Dawn L. DeMeo reported in a poster session at an international conference of the American Thoracic Society.
“This is crucial, especially from a public health standpoint, because many people feel that one, two, or five cigarettes per day is fine,” Dr. DeMeo, assistant professor of medicine at Harvard Medical School and the Channing Laboratory, Boston, said in an interview. “What we want to promulgate from this study is that there is no safe exposure to cigarette smoke, especially for young women.”
She and her associates evaluated data from a case-control study performed at Haukeland University Hospital in Bergen, Norway, between 2003 and 2005 that involved 583 men and 371 women with chronic obstructive pulmonary disease (COPD). To be eligible for the trial, participants had to be white, at least 40 years of age, and current or ex-smokers with a history of 2.5 pack-years or more, and they had to have no severe alpha-1 antitrypsin deficiency.
The researchers observed no differences between men and women with respect to lung function and COPD severity, but the women were younger (a mean of 64 vs. 66 years) and had smoked significantly less than men (a mean of 24 vs. 32 pack-years).
Dr. DeMeo and her associates then restricted the analysis to two subgroups: an early-onset group of 316 patients who were younger than age 60 at the time of the study and a lower-exposure group of 241 patients with a smoking history of fewer than 20 pack-years. Analysis of these subgroups revealed that females had a later smoking onset and fewer pack-years compared with males.
Women in the study also had a more severe reduction of forced expiratory volume in 1 second for lower levels of smoking exposure, but after 25–30 pack-years the curves for males and females converged and showed a similar dose-response relationship.
“There seems to be a female predominance for the lung-damaging effects of cigarette smoke, but it seems to be most pronounced when the cigarette smoke exposure is on the lower end,” said Dr. DeMeo, who is also with Brigham and Women's Hospital's lung transplantation program and the COPD center at the Center for Chest Diseases.
Reasons for the gender differences remain unclear, but could be related to the fact that women have smaller lungs than men. “That likely doesn't explain all of the potential impact here,” she commented.
“There have been hormonal arguments cited and also social constructs associated with gender differences. Perhaps women are underreporting [their cigarette smoking]. One of the goals of our research group at the Channing Laboratory is to address what may be going on from genetic and epigenetic points of views. More research is needed,” she said.
For now, Dr. DeMeo added, “the onus is on clinicians to think about COPD early, especially in women who report lower exposures to cigarette smoking.”
She acknowledged certain limitations of the study, including its retrospective design and the fact that it was conducted only in Norwegian whites.
The study received funding from the Research Council of Norway, GlaxoSmithKline, and the Foundation for Respiratory Research at Haukeland University Hospital. Dr. DeMeo was supported by a grant from the National Institutes of Health and an award from the Doris Duke Charitable Foundation.
In smokers with similar COPD severity, women had less exposure to cigarettes. ©