According to the Journal of the American Medical Association, Women who quit smoking cut the biggest risks of death from heart disease “significantly” within five years and have a 20 percent lower chance of dying from related cancers in that time.

The study’s authors, led by Stacey A. Kenfield of Harvard University’s School of Public Health in Boston, analyzed post- 1980 data from the Nurses’ Health Study, a survey of almost 105,000 nurses conducted starting in 1976. The study will be published in the May 7th issue of JAMA

Researchers found that the risk of death was reduced by 13 percent within the first five years after quitting smoking, mostly due to a lower chance of dying from coronary heart disease, and dropped to the level of a person who had never smoked after 20 years.

“Our main message here is that the harms of smoking are reversible,” Kenfield said in a telephone interview from Boston yesterday. “For some causes of death, the reduction is much higher within the first five years. So it’s never too late to quit smoking. But we also saw a reduction in other diseases, so the message is that it’s never too late to stop even though you may have been smoking for many, many years.”

Smoking is the leading preventable cause of death across the globe, with more than 5 million people dying from lung cancer, heart disease and other illnesses annually, according to the World Health Organization. That figure may rise to 10 million a year by 2030.

Follow-Up Studies

The chance of dying from lung cancer dropped 21 percent within five years after quitting when compared with people who continued to smoke, although additional risk didn’t disappear for 30 years, the study said.

Former smokers who had quit 20 to 30 years earlier had an 87 percent lower chance of dying from lung cancer when compared with current smokers, the study said. The risk dropped to the same level as a person who had never smoked after 20 years for all smoking-related cancers, which include lip, mouth and stomach cancers.

The risk of death from respiratory disease dropped 18 percent within a decade after quitting, and approached the same level as a person who had never smoked after 20 years.

Unlike previous studies, the authors followed up with the survey respondents every two years to ask about their smoking status, which Kenfield said made the findings more accurate.

Other studies “did not see a drastic decrease in risk especially with people that had quit smoking for a long time,” Kenfield said. For chronic obstructive pulmonary disease and lung cancer, “we saw a very nice decline in risk down to the level of a non-smoker over time.”