A new Harvard study provides even further incentive to quit smoking. It finds that women can reduce their risk of dying from smoking-related causes within just a few years after swearing off cigarettes.

Researchers from the Harvard School of Public Health found that within five years of quitting smoking, a woman's overall risk of death dropped by 13 per cent. Twenty years after quitting, her risk of death dropped to be on par with that of a woman who has never smoked.

"Tobacco use remains the leading preventable cause of death in the United States," the study's authors wrote.

"Globally, approximately five million premature deaths were attributable to smoking in 2000. The World Health Organization projects by 2030 that tobacco-attributable deaths will annually account for 3 million deaths in industrialized countries and 7 million in developing countries."

The research team analyzed data from over 100,000 women who participated in the Nurse's Health Study who were followed up for more than 20 years, beginning in 1980. The study was published in the Journal of the American Medical Association.

The researchers also found:

  • the risk of death from respiratory disease dropped by 18 per cent between five and 10 years after quitting smoking, and was comparable to that of a never smoker after 20 years.
  • the risk of death from lung cancer dropped by 21 per cent within the first five years of quitting smoking, with an 87 per cent reduced risk of death between 20 and 30 years after quitting.
  • 20 years after quitting, a smoker's risk of death from all smoking-related cancers dropped to be the same risk as that of a never smoker.
  • the risk of death for smokers was 22 per cent higher among women who picked up the habit before age 17 versus those who started smoking at age 26 or later.

"Effectively communicating risks to smokers and helping them quit successfully should be an integral part of public health programs," the authors concluded.

Abstract:

Smoking and Smoking Cessation in Relation to Mortality in Women

Stacey A. Kenfield, ScD, Meir J. Stampfer, MD, DrPH, Bernard A. Rosner, PhD, Graham A. Colditz, MD, DrPH

Context: Smoking is associated with an increased risk of total and cause-specific death, but the rate of mortality risk reduction after quitting compared with continuing to smoke is uncertain. There is inadequate or insufficient evidence to infer the presence or absence of a causal relationship between smoking and ovarian cancer and colorectal cancer.

Objective: To assess the relationship between cigarette smoking and smoking cessation on total and cause-specific mortality in women.

Design, Setting, and Participants: Prospective observational study of 104 519 female participants in the Nurses' Health Study with follow-up from 1980 to 2004.

Main Outcome Measure: Hazard ratios (HRs) for total mortality, further categorized into vascular and respiratory diseases, lung cancer, other cancers, and other causes.

Results: A total of 12 483 deaths occurred in this cohort, 4485 (35.9%) among never smokers, 3602 (28.9%) among current smokers, and 4396 (35.2%) among past smokers. Compared with never smokers, current smokers had an increased risk of total mortality (HR, 2.81; 95% confidence interval [CI], 2.68-2.95) and all major cause-specific mortality. The HR for cancers classified by the 2004 surgeon general's report to be smoking-related was 7.25 (95% CI, 6.43-8.18) and 1.58 (95% CI, 1.45-1.73) for other cancers. Compared with never smokers, the HR for colorectal cancer was 1.63 (95% CI, 1.29-2.05) for current smokers and 1.23 (95% CI, 1.02-1.49) for former smokers. A significant association was not observed for ovarian cancer. Significant trends were observed for earlier age at initiation of smoking for total mortality (P=.003), respiratory disease mortality (P=.001), and all smoking-related cancer mortality (P=.001). The excess risk for all-cause mortality decreases to the level of a never smoker 20 years after quitting, with different time frames for risk reduction observed across outcomes. Approximately 64% of deaths among current smokers and 28% of deaths among former smokers were attributable to cigarette smoking.

Conclusions: Most of the excess risk of vascular mortality due to smoking in women may be eliminated rapidly upon cessation and within 20 years for lung diseases. Postponing the age of smoking initiation reduces the risk of respiratory disease, lung cancer, and other smoking-related cancer deaths but has little effect on other causespecific mortality. These data suggest that smoking is associated with an increased risk of colorectal cancer mortality but not ovarian cancer mortality.