Passage of time reduces smoking mortality risk for women who quit

3 min read

For lung cancer, 30 years needed to completely eliminate increased mortality risk

Women who quit smoking significantly reduce their risk of
death from coronary heart disease within 5 years and have about a 20
percent lower risk of death from smoking-related cancers within that
time period, according to a study by researchers at the Harvard School of Public Health (HSPH).

“Tobacco use remains the leading preventable cause of death in the
United States. Globally, approximately 5 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 authors write in the May 7 issue of JAMA – the Journal of the American Medical Association.

Stacey A. Kenfield, an HSPH research fellow and colleagues assessed the relationship between cigarette smoking and smoking cessation on total and cause-specific mortality in women by analyzing data from the Nurses’ Health Study, an observational study of 104,519 female participants, with follow-up from 1980 to 2004. A total of 12,483 deaths occurred in this group, 4,485 (35.9 percent) among never smokers, 3,602 (28.9 percent) among current smokers, and 4,396 (35.2 percent) among past smokers.

The researchers found a significant 13 percent reduction in the risk of
all-cause mortality within the first 5 years of quitting smoking
compared with continuing to smoke, and the excess risk decreased to the
level of a never smoker 20 years after quitting, with some causes taking
more or less time. “Significant trends were observed with increasing
years since quitting for all major cause-specific outcomes. A more rapid
decline in risk after quitting smoking compared with continuing to smoke
was observed in the first 5 years for vascular diseases compared with
other causes.”

“Much of the reduction in the excess risk for these causes of death were
realized within the first 5 years for coronary heart disease and
cerebrovascular disease. Sixty-one percent of the full potential benefit
of quitting in regard to coronary heart disease mortality and 42 percent
of the full potential benefit of quitting in regard to cerebrovascular
mortality was realized within the first 5 years of quitting smoking,
when comparing hazard ratios for recent quitters of less than 5 years
with long-term quitters of 20 years or greater. For death due to
respiratory disease, an 18 percent reduction in risk of death was
observed 5 to 10 years after quitting smoking, with the risk reaching
that of a never smoker’s risk after 20 years.”

For lung cancer mortality, a significant 21 percent reduction in risk
was observed within the first 5 years compared with continuing smokers,
but the excess risk did not disappear for 30 years. Past smokers with 20
to less than 30 years of cessation had an 87 percent reduction in risk
of lung cancer mortality compared with current smokers. When including
the other smoking-related cancers, the excess risk approached a never
smoker’s risk more than 20 years after quitting smoking.

Significant trends were observed for earlier age at initiation of
smoking for total mortality, respiratory disease mortality, and all
smoking-related cancer mortality. The data also suggested that smoking
is associated with an increased risk of colorectal cancer mortality but
not ovarian cancer mortality. The researchers also found that
approximately 64 percent of deaths among current smokers and 28 percent
of deaths among former smokers were attributable to cigarette smoking.

“Early age at initiation is associated with an increased mortality risk
so implementing and maintaining school tobacco prevention programs, in
addition to enforcing youth access laws, are key preventive strategies.
Effectively communicating risks to smokers and helping them quit
successfully should be an integral part of public health programs,” the
authors conclude.