Statement on Oral Contraceptive Study from Barbara
Alving, M.D., Director of the Women’s Health
Initiative and Acting Director of the National Heart,
Lung, and Blood Institute
A Women’s Health Initiative (WHI) review of
a recent abstract on the effects of oral contraceptive
use on cardiovascular disease has found flaws in both
the design and interpretation of the WHI data used
in the study. The October presentation of the abstract
at the annual scientific meeting of the American Society
of Reproductive Medicine – and subsequent media
coverage – may have created the impression that
OC use is linked to lower risk of cardiovascular disease
(CVD). However, the WHI review of the abstract shows
no evidence that OC use is linked to lower risk of
CVD.
The abstract used information provided by WHI participants
at baseline when they first joined the study. Such
analyses are limited and considered exploratory and
they should not be used to reassure women about OC
use. There is a large and reputable body of higher
scientific evidence linking current OC use to future
increases in risk of stroke and heart attack, especially
in older women and in smokers. The abstract bears
no relationship to the findings from the WHI clinical
trials of hormones, which showed that postmenopausal
hormone use clearly does not reduce, and in fact may
increase the risk for CVD.
The presentation of the abstract was not made on behalf
of the Women’s Health Initiative (WHI) and it
had not been reviewed by WHI or by the National Heart,
Lung, and Blood Institute (NHLBI) prior to presentation
in Philadelphia. The data in the abstract have now
been reviewed by senior statisticians at the WHI Clinical
Coordinating Center. They repeated the analysis for
OC and CVD in the WHI baseline data. They controlled
for age and other factors and could not find a relationship
between OC use and cardiovascular disease. The statisticians
also doubt the validity of a separate cancer abstract
which used WHI baseline data to examine OC cancer
risks. They conclude that the cancer analyses have
the same potential for finding misleading results
as occurred with the CVD analysis. Therefore, these
kinds of data are not suitable for the exploration
of any link between OC use and cancer.
In general, randomized controlled clinical trials
provide the highest quality evidence to answer scientific
questions. Analyses using baseline data, such as the
one described in the recent presentation, have biases
and errors that raise doubts about the validity of
any associations found in the exploratory analyses.
It is important to understand that WHI data come only
from postmenopausal women who were 50 to 79 years
of age when they joined the study. The recent presentation
was based on women’s recall of their past OC
use and diseases they thought they developed. Because
people can forget details, the best studies try to
collect these data as close to the event as possible
and to confirm any report of disease with hospital
records.
For any valid analysis of the effect of OC use on
cardiovascular disease it would be important to control
adequately for factors such as age, body weight, blood
pressure, smoking, high blood cholesterol, and diabetes.
All of these factors may be related to whether women
used OCs and whether they had CVD. The age of women
when they enrolled is particularly important, since
OCs were not available to older women and CVD is strongly
related to age. For a more complete discussion of
these points, see the WHI
study website (www.whi.org/news/).
Other research studies have found that women who take
OCs have a small increased risk for CVD, like blood
clots, heart attacks, and stroke. These studies provide
better scientific data than the recent analysis because
they focused on specific questions about OCs and CVD.
Research conducted in the past to answer specific
questions about OCs and breast cancer has shown an
increased risk of breast cancer in women who have
recently used OCs. Past research has also shown a
decreased risk of ovarian cancer and a slight decreased
risk of endometrial (uterine) cancer in women who
use some types of OCs. Information on risks and side
effects of OCs is available from the U.S.
Food and Drug Administration (www.fda.gov) and
from the National
Cancer Institute (www.nci.nih.gov).
WHI is funded by the National Heart, Lung, and Blood
Institute and conducted in collaboration with the
National Institute on Aging, the National Cancer Institute,
the National Institute for Arthritis, Musculoskeletal
and Skin Disorders, and the NIH Office of Women's
Health Research.
NHLBI is part of the National Institutes of Health
(NIH), the Federal Government’s primary agency
for biomedical and behavioral research. NIH is a component
of the U.S. Department of Health and Human Services.
Additional information on menopausal hormone therapy,
including the WHI estrogen-plus-progestin study, can
be found on the NIH Website
(www.nih.gov), on the NHLBI
Website (www.nhlbi.nih.gov), and on the FDA
Website (www.fda.gov).
For more information:
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