Risk of lung cancer death has risen dramatically among women smokers in recent decades

The researchers analyzed 7 cohort studies -- studies that follow a large group of people over time -- to compare women's smoking patterns and risk of death from smoking-related diseases to that of men over the past 50 years. In total the study included more than 2.2 million adults age 55 years and older. They found that as women began to smoke more like men, by starting younger and smoking more cigarettes per day, their risk of death rose to equal that of men.

The study was published in the January 24, 2013 issue of the New England Journal of Medicine.

Effects of smoking take decades

Men in the US began smoking cigarettes in large numbers in the early 20th century, but it wasn't until decades later that large numbers of women began smoking regularly. In addition, women who began smoking in the 1950s or later started smoking at an earlier age and smoked more heavily. Daily cigarette consumption peaked during the 1970s among male smokers and during the 1980s among female smokers. Since then, smoking for both groups has decreased.

As lifetime smoking behaviors for men and women have become increasingly similar, risks of death from smoking have also become similar. The relative risks of death from lung cancer, COPD, stroke, and heart disease are now nearly identical for female and male smokers. The risk of death from lung cancer appears to have stabilized among male smokers since the 1980s, but continues to increase among female smokers.

For women who smoked in the 1960s, the risk of dying from lung cancer was 2.7 times higher than that of nonsmokers. The risk of dying from COPD was 4 times higher among smokers than nonsmokers. From 2000-2010, the risk of female smokers dying from lung cancer was 25.7 times higher than the risk in nonsmokers. The risk of dying from COPD was 22.5 times higher than that for nonsmokers. About half the increase in risk of both conditions occurred during the last 20 years.

The rate of death from all causes is also now nearly identical for male and female smokers. For men over 55 and women over 60, the rate of death from all causes combined is now at least 3 times greater among current smokers as among people who have never smoked.

More long-term implications

The study also found that the risk of death from COPD among male smokers continues to increase, even though male smokers' lung cancer death rate has remained about the same since the 1980s. Lead researcher Michael J. Thun, MD, who recently retired as vice president emeritus of the American Cancer Society, said changes in cigarette design may have contributed to this increase. Thun said diluted smoke from cigarettes labeled as "light" and "mild" is inhaled more deeply, exposing more of the lung tissue to the smoke.

Dr. Thun said this study has important implications for developing countries, where smoking has increased relatively recently among men. He said, "Our study shows the full effects of smoking don't become apparent for 50 or more years. The increased risk developing countries are observing now is a small prelude to the risk they can expect to observe later. Smoking killed about 100,000 people worldwide in the 20th century. If current patterns persist, it will kill about a billion people in the 21st century. Preventive measures to reduce smoking among men and prevent the uptake of smoking among women is a massive opportunity for prevention."

The study also confirms that quitting smoking at any age dramatically lowers the risk of death from all major smoking-related diseases, and that quitting altogether is much more effective than smoking fewer cigarettes.