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Wednesday, May 7, 2008

Women Who Quit Smoking Quickly Reduce Heart Risk But Lungs Take Longer

Women who quit smoking significantly reduce risk of death from coronary heart disease within 5 years, but impact on risk of death from lung and other cancers take longer.

These are the findings of Dr. Stacey A Kenfield, of the Harvard School of Public Health, Boston, USA, and colleagues in a new study published in the May 7th issue of the Journal of the American Medical Association, JAMA.

According to the World Health Organization, about 5 million deaths were smoking related in 2000, and estimates suggest that by 2030, this figure will rise to 10 million worldwide, 7 million of which will be in developing countries, wrote the authors, who also said that tobacco use is the leading cause of death in the United States.

But while the link between smoking and increased risk of death from a range of diseases has been well established, the effect of quitting compared to continuing to use tobacco has not.

Kenfield and colleagues examined data from the Nurses' Health Study on over 100,000 women who were followed from 1980 to 2004. In this group there were nearly 12,500 deaths, with nearly 4,500 among never smokers (36 per cent), 3,600 among current smokers (29 per cent) and just under 4,400 among past smokers (35 per cent).

They calculated the relative risks (as hazard ratios) among the three subgroups of death from any cause, and from specific diseases such as cardiovascular, respiratory, lung and other cancers, and other causes.

The results showed that:

* There was a 13 per cent reduction in the risk of death from any cause within the first 5 years of quitting compared to continuing to smoke.

* This risk reduced to the same level as the never smokers after 20 years of quitting.

* Within this overall 20 year figure some causes took less time to go down to the never smokers' risk level and others took longer.

* Vascular disease showed the most rapid reduction in risk to the never smokers' level, with much of it showing in the first 5 years of quitting.

* These included coronary heart disease (62 per cent of excess risk gone in first 5 years of quitting) and cerebrovascular disease (42 per cent of excess risk gone in first 5 years of quitting).

* These figures were obtained from comparing the hazard ratios of recent quitters of less than 5 years with long term quitters of 20 years or more.

* Death from respiratory diseases showed an 18 per cent reduction in risk of death 5 to 10 years after quitting, going down to the never smokers' level after 20 years.

* Risk of death from lung cancer showed a significant 21 per cent reduction in the first 5 years of quitting compared to continuing to smoke, but the excess risk did not go away for 30 years.

* Past smokers who had quit for 20 but less than 30 years, had an 87 per cent reduction in risk of death from lung cancer compared to current smokers.

* When risk of death from other smoking-related cancers was included, this figures approached the never smokers' risk level more than 20 years after quitting.

* Risk of death from all causes, respiratory diseases, and smoking related cancers, was significantly higher among women who started smoking at a younger age.

* The figures also showed smoking was linked to increased risk of death from colorectal cancer but not ovarian cancer.

* About 64 per cent of deaths among current smokers and 28 per cent among past smokers were linked to cigarette smoking.

The authors concluded that:

"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."

They added that:

"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 cause-specific mortality. These data suggest that smoking is associated with an increased risk of colorectal cancer mortality but not ovarian cancer mortality."

The researchers emphasized the importance of maintaining school programs on preventing tobacco use and enforcing laws that deny young people access to tobacco, given that early initiation is linked to higher risk of death. They also wrote that:

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

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