Smoking-specific mortality risk reversible after cessation

May 6, 2008

NEW YORK (Reuters Health) - Smoking-related deaths are substantially reduced within 5 years after smoking cessation, according to long-term prospective follow-up of the Nurses' Health Study cohort, reported in the Journal of the American Medical Association for May 7th.

"Because there is a rapid decline in risk for some diseases, it's never too late to quit smoking," Dr. Stacey A. Kenfield of the Harvard School of Public Health in Boston told Reuters Health. "However, a former smoker's risk for other diseases does not decline to the level of nonsmokers for 20 or more years, so it is never too early to quit smoking, either."

Dr. Kenfield and her team analyzed outcomes for 104,519 women who were 34 to 59 years old in 1980. Subjects' information was updated every 2 years through 2004.

A total of 12,483 deaths occurred. Compared with never smokers, the risk of all-cause mortality was nearly 3-fold higher among current smokers, and the risk of mortality from smoking-related cancers was increased 7-fold.

"Studies that do not update smoking status of their participants during follow-up are likely to overestimate the amount of time needed to reduce one's risk to the level of a non-smoker," Dr. Kenfield noted.

For example, after 5 years of smoking cessation, mortality due to coronary heart disease is reduced by almost half, and mortality from lung cancer is about 20% lower. "This rapid decline in risk for some diseases can help provide motivation to (smokers) who are thinking about quitting," she said.

Other studies that did not update participants' records after baseline "found that the risks of COPD and lung cancer remained highly elevated even after 20 years," she continued. "We found that the risks decreased to the level of non-smokers after 20 years for COPD and 30 years for lung cancer."

The large cohort size and length of follow-up permitted the researchers to re-examine causal associations for which previous evidence had been inconclusive.

"Importantly, we found a 58% increase in risk of dying from other cancers that are not thought to be associated with smoking," Dr. Kenfield said. "One of these cancers is colorectal cancer, where current smokers had a 63% increased risk of dying and former smokers had a 23% increased risk of dying, compared to non-smokers."

Public health initiatives to keep teenagers from smoking should considerably reduce smoking-related mortality. "We found that postponing age at starting to smoke had a huge impact on reducing risk of respiratory diseases and smoking-related cancers."

The research team believes their findings can also be applied to men with a similar smoking profile as the women in the Nurses Health Study.

"Data on the speed at which risk decreases after stopping may help smokers understand the value of stopping smoking and the health benefits they will gain from succeeding," Dr. Kenfield concluded.