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Date: Wednesday, April 23, 1997 FOR IMMEDIATE RELEASE National Institutes of Health, NCI Press Office (301) 496-6641
The mortality risks associated with cigarette smoking are significantly
greater today than they were when these risks were presented in
the first Surgeon General's
Report in 1964, particularly for women, according to a new report
released by the National Cancer Institute (NCI).
The 565-page monograph, Changes in Cigarette-Related Disease
Risks and Their Implication for Prevention and Control contains
newly analyzed data from five of the world's
largest epidemiologic studies on smoking and health.
Two of the studies began in the 1950s when an understanding of
the health effects of smoking was just beginning to emerge, while
the other three studies started more recently. Study populations
ranged from 60,000 to 1.2 million and the length of follow-up
varied from six to 26 years. A total of nearly 490,000 deaths
was available for analysis across all studies. Taken as a group,
these five studies represent over 20 million person-years of observation.
According to the new monograph, the risks for all smoking-related
causes of death, including lung cancer, other cancers, heart disease,
stroke, and chronic obstructive lung diseases have increased among
both men and women. And while men who smoke still experience higher
risks for these diseases than women, the greatest increases in
risks were found in female smokers. "The findings are extremely troubling for anyone concerned with public
health," said NCI Director Richard D. Klausner, M.D. "Especially
troubling is the large increase in relative risks observed among
women for cancer of the lung and other smoking-related cancer
sites. We must do all we can to continue to keep women fully informed
about the dangers of cigarette smoking."
The increase in mortality risk occurred during a time when significant
declines in machine-measured tar and nicotine yields of cigarettes were being
reported. The average tar level per cigarette has declined nearly
70 percent since 1955, from approximately 38 mg to 12.5 mg today.
Similarly, nicotine levels fell from an average of 2.6 mg per
cigarette to under 0.9 mg over the same time period. Yet the relative
risks for all major smoking-related causes of deaths increased.
David M. Burns, M.D., the monograph's senior editor, of the University of California,
San Diego, said the increase in relative risk was due to a greater
lifetime dose of cigarette smoke received by smokers in the more
recent studies compared with smokers included in the studies from
the 1950s and early 1960s. For example, women in the contemporary
studies started smoking in their teens, while many of those in
the older studies began smoking later in life.
According to Burns, "Smokers in the newer studies consumed more cigarettes per day than smokers
followed in earlier studies, and much of the difference between
the two sets of risks disappears when duration of smoking history
and number of cigarettes smoked per day are held constant."
A substantial literature base also exists which clearly shows
that smokers today are smoking each cigarette more intensively
than smokers did 40 years ago, with larger puffs and deeper patterns
of inhalation, added Burns, but it is unclear to what degree these
differences have contributed to the observed increase in mortality
risks.
In the new analysis, American Cancer Society (ACS) investigators
compared six-year follow-up data from two ACS studies known as
Cancer Prevention Studies (CPS) I and II (see table). CPS I was
initiated in 1959 while CPS II began in 1982. The two studies
used nearly identical study designs and methodologies, and each
included more than 1 million persons. These studies essentially
represent two groups of smokers born approximately a generation
apart.
The difference in lung cancer risk between men who smoked and those who did not smoke doubled between studies. In statistical terms, the relative risk increased from 11.9 to 23.2. Relative risk is a ratio used to compare the probabilities of an outcome such as cancer in two different groups. Smokers studied in CPS I were about 12 times more likely than nonsmokers to die of lung cancer, while smokers studied in CPS II were about 23 times more likely than nonsmokers. Among women, the relative risk increased more than fourfold, from 2.7 in CPS I women to 12.8 in CPS II.
The morality risks for all other smoking-related cancers combined,
which included cancers of the larynx, oral cavity, esophagus,
bladder, kidney, and pancreas, increased from 2.7 to 3.5 in male
smokers and from 1.8 to 2.6 among females smokers. Relative risk
for coronary heart disease (CHD) for men rose from 1.7 in CPS
I to 2.3 in CPS II, while the CHD risks in female smokers rose
from 1.4 to 1.8. Similar increases were noted for other causes
of death.
Results from two other studies that began in the 1970s confirm
the results observed among female smokers in CPS II. Data based
on 36,035 women in the Kaiser Permanente Study and 121,700 women
in the Nurses' Health Study show that women smokers had nearly twice the risk of death
from all causes compared with women who did not smoke. This relative
risk of 1.9 was identical to the relative risk found for women
in CPS II. Among women in the Kaiser Permanente Study, relative
risks for all the major smoking-related diseases were similar
to those found among women in CPS II.
For example, the mortality risk for lung cancer among women smokers
in the Kaiser Permanente Study was 15.1, compared with 12.8 among
CPS II women. For CHD, the relative risks were 1.7 and 1.8 in
Kaiser and CPS II, respectively; and for chronic obstructive lung
disease the relative risks were 9.0 in Kaiser and 12.8 in CPS
II.
"The major prospective studies summarized in the monograph are important cornerstones for documenting smoking-induced diseases," said Donald Shopland, coordinator of NCI's Smoking and Tobacco Control Program, "not only because of the size of the populations involved but because the participants were essentially healthy at the start of the studies."
Shopland added that the findings make clear the enormous risks
posed by cigarette smoking. Preventing adolescent smoking will
have the greatest benefit for society in the long run, however,
the benefits of cessation to adults who currently smoke are substantial,
and declines in smoking among this group could reduce death rates
in as little as five years.
Health professionals may order single copies of Changes in Cigarette-Related Disease Risks and Their Implication for Prevention and Control from the NCI's Cancer Information Service at 1-800-4-CANCER. A summary of the publication will also be available.
Attachment: Characteristics of Study Populations for Five Major
Prospective Studies reported in Changes in Cigarette-Related
Disease Risks and Their Implication for Prevention and Control.
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Characteristics of Study Populations for Five Major Prospective Studies
Study Year Initiated | Total Size of cohort | % of females in cohort | Years of follow up | Approx. number of deaths |
U.S. Veterans 1954 | 300,000 |
< 1% | 26 years | 198,000 |
CPS I* 1959 | 1,078,894 |
52% | 12 years | 205,000 |
Kaiser Permanente 1979 | 60,838 | 59% |
6.1 years** | 3,000 |
Nurses Health Study 1976 | 121,700 | 100% | 12 years | 2,800 |
CPS II* 1982 | 1,185,106 |
57% | 6 years | 79,800 |
* CPS = Cancer Prevention Study
** Mean number of years follow up