Investigators believe
teachers tend to share certain lifestyle and environmental factors that may
help protect them from cancer or increase their risk.
They found these
characteristics among participating teachers and compared them to similar
women throughout California:
They found these
characteristics among participating teachers and compared them to similar
women throughout California:
|
Teachers
|
California women |
Average age at
first menstruation |
12.5 years |
12.9 years |
Never pregnant
|
21 percent |
14 percent |
Average age at
first pregnancy |
26.4 years |
23.7 years |
Average number of
live births |
2.3 |
2.7 |
Has had a
hysterectomy |
24 percent |
29 percent |
Body mass index
less than 25 |
61 percent |
53 percent |
Has never smoked
cigarettes |
67 percent |
55 percent |
One factor that
increases breast cancer risk in teachers is alcohol consumption. "It's
important to note, however, that the increased risk for breast cancer was
for women consuming two or more glasses of an alcoholic beverage a day.
Consuming one glass a day, which research has found is good for a woman's
heart, does not increase the risk of breast cancer," says Pamela Horn-Ross,
Ph.D., senior research scientist at NCCC and lead author of a previous
report from the study that appeared in Cancer Causes and Control
earlier this year.
No one knows exactly
why, but women with more education and income are at higher risk for breast
cancer. This is at least partly because women who delay having their first
child and have fewer children until after college or starting a career,
for example are at increased risk.
Breast, ovarian and
endometrial cancers share some of these reproductive risk factors. Teachers
in the study tended to have their first baby later and had fewer children in
total. Teachers also had high rates of use of hormone replacement therapy,
which may be linked to breast cancer. These factors, however, do not appear
to entirely explain the excess risk.
Meanwhile, cervical
cancer, a disease occurring less frequently among teachers, can be prevented
through Pap testing and a substantial 91 percent of participants reported
having a Pap test sometime within the previous two years. Smoking was low
among teachers, which might explain the reduced lung cancer incidence among
them.
In the coming years,
the investigators will continue to follow the women in the study and look at
family history, diet and environment. Horn-Ross, for one, will examine
relationships between dietary patterns including isoflavones, the
phytoestrogens that are present in soy and the risk of breast, endometrial
and other cancers.
Teachers have long
been suspected to be at high risk for breast cancer. The study grew out of
reports of excess incidence of breast and other cancers among women in
California school systems.
Although no one can
prevent cancers from occurring in the population, people can take steps to
lower their risks. General recommendations include avoiding smoking, eating
a healthy diet and exercising. More information on cancer risk reduction is
available from the National Cancer Institute's Cancer Information Service
(1-800-4-CANCER), which in California is operated by the NCCC.
The study was
supported by the California Breast Cancer Act of 1993 (tobacco tax), the
California Department of Health Services and the National Cancer Institute.
# # #
Leslie Bernstein,
Mark Allen, Hoda Anton-Culver, Dennis Deapen, Pamela L. Horn-Ross, David
Peel, Richard Pinder, Peggy Reynolds, Jane Sullivan-Halley, Dee West,
William Wright, Al Ziogas and Ronald K. Ross, "High breast cancer incidence
rates among California teachers: results from the California Teachers Study
(United States)." Cancer Causes and Control. September 2002, Vol. 13,
No. 7.
2002 Northern California Cancer Center, NCCC Web Team