People who quit smoking will see a rapid decline in the risk of death from coronary heart disease (CHD) and other vascular disorders, a new analysis of the Nurses' Health Study shows [1].

And although the study participants were all women, lead author Dr Stacey Kenfield (Harvard Medical School, Boston, MA) told: "We feel that we can generalize our findings to men who have a similar smoking profile."

Kenfield and colleagues report their findings in the May 7, 2008 issue of the Journal of the American Medical Association.

They found that 61% of the full benefit of quitting in regard to CHD mortality and 42% of the full benefit of quitting in regard to cerebrovascular deaths was realized within the first five years of stopping smoking.

"The harms of smoking are reversible, but for some causes of death, the reduction takes many years, so it's never too early to quit smoking.

On the other hand, for some diseases—eg, CHD—there is a rapid decline in risk, so it's never too late to stop smoking, even if you've been smoking for many, many years," Kenfield noted.

It's never too late to stop smoking, even if you've been smoking for many, many years

In their analysis, the researchers have included an additional 16 years of follow-up from the original Nurses' Health Study cohort report, including a total of 12 483 deaths, and updated estimates for total mortality, further categorized into CHD, cerebrovascular disease, respiratory disease, chronic obstructive pulmonary disease (COPD), a range of cancers, and other causes.

They point out that the smoking status of participants was updated every two years, enabling a more accurate evaluation of the detrimental effects from long-term smoking and the risk reduction over time from sustained cessation.

Other studies—which have not updated smoking exposure over time or used smoking information just before diagnoses—may obscure the harms of continuing to smoke and the benefits of cessation, they note, "because current smokers may quit smoking over time and some past smokers may resume smoking."

Participants were classified as never, past, or current smokers, with current smokers split into categories of one to 14 cigarettes per day, 15 to 24, 25 to 34, and 35 or more.

The relationship between an increasing risk of death with increasing numbers of cigarettes smoked per day varied by disease outcome—the trend was less pronounced for vascular disease, suggesting that the first few cigarettes account for most of the increased risk; in contrast, an increased number of cigarettes smoked per day substantially increased the risk of death from respiratory disease.

• a. All covariates, including smoking, updated until diagnosis of disease
• b. Includes CHD and cerebrovascular disease

Smokers were also categorized with regard to the age at which they started smoking: 17 years or younger, 18 to 21, 22 to 25, and 26 years or older. For vascular disease, the age of starting smoking seemed to play less of a role in determining the risk of death than it did for respiratory disease, lung cancer, and other smoking-related cancer mortality.

• a. All covariates, including smoking, updated until diagnosis of disease
• b. Includes CHD and cerebrovascular disease
• c. Adjusted for age, follow-up period, history of hypertension, diabetes, high cholesterol, body-mass index, change in weight from age 18 to baseline (1980), alcohol intake, physical activity, previous use of oral contraceptives, postmenopausal estrogen therapy use and menopausal status, parental history of MI at age 65 years or younger, cigarettes smoked per day during the period prior to quitting, and age at starting smoking

For the cessation analysis, past smokers were classified into categories of time since quitting: less than five years, five to less than 10 years, 10 to less than 15 years, 15 to less than 20 years, and 20 or more years.

A more rapid decline in risk after quitting smoking compared with continuing to smoke was observed in the first five years for vascular diseases compared with other causes: 61% of the full benefit of quitting with regard to CHD death and 42% of the benefit of quitting with regard to cerebrovascular death was realized within five years of stopping smoking.

In contrast, it took much longer for the excess mortality risk associated with respiratory disease and smoking-related cancers to approach that of a never smoker: 20 years for COPD and 30 years for lung cancer.

• a. All covariates including smoking updated until diagnosis of disease
• b. Adjusted for age, follow-up period, history of hypertension, diabetes, high cholesterol, body-mass index, change in weight from age 18 to baseline (1980), alcohol intake, physical activity, previous use of oral contraceptives, postmenopausal estrogen therapy use and menopausal status, parental history of MI at age 65 years or younger, cigarettes smoked per day during the period prior to quitting, and age at starting smoking
• c. Includes CHD and cerebrovascular disease

Kenfield concluded:

"We want current smokers to stop smoking, and if we can't prevent people from starting to smoke at all, we at least need to postpone the age at which they start.

Other studies show the earlier someone starts smoking, the higher his or her chances are of becoming a regular smoker and the less likely he or she is to quit."

1. Kenfield SA, Stampfer MJ, Rosner BA, et al. Smoking and smoking cessation in relation to mortality in women. JAMA 2008; 299: 2037-2047.