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 ears 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
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).