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Barbara Davis Center for Childhood Diabetes (J.K.S.-B., G.L.K., M.R.) and Departments of Preventive Medicine and Biometrics (D.D., L.G.O., J.E.H.) and Medicine (J.E.), University of Colorado at Denver and Health Sciences Center, Denver, Colorado 80045; and George Washington University Medical Center (J.E.), Washington, D.C. 20037
Address all correspondence and requests for reprints to: Janet K. Snell-Bergeon, Barbara Davis Center for Childhood Diabetes, University of Colorado at Denver and Health Sciences Center, P.O. Box 6511, Mail Stop A-140, Aurora, Colorado 80045. E-mail: janet.snell-bergeon{at}uchsc.edu.
| Abstract |
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Objective: The purpose of this study was to determine whether coronary artery calcium (CAC) is associated with menstrual dysfunction and BC use in women with T1D.
Materials and Methods: This was a prospective cohort study, and participants were followed up for an average of 2.4 yr.
Patients: Patients included 612 women (293 T1D, 319 Non-DM) between the ages of 19 and 55 yr who had CAC measured twice by electron beam tomography.
Results: Irregular menses and amenorrhea were more common in T1D than Non-DM women (22.1 vs. 14.9%, P < 0.05 and 16.6 vs. 7.0%, P < 0.001). T1D women reported less BC use than Non-DM women (79.8 vs. 89.9%, P < 0.001) and reached menarche at an older age (13.1 ± 1.8 vs. 12.8 ± 1.5 yr, P < 0.05). Use of BC was associated with less CAC progression in all women, but this association was stronger in T1D women (P value for interaction = 0.02). Irregular menses were associated with greater CAC progression only among T1D women.
Conclusions: A prior history of BC use is associated with reduced CAC progression among all women, with a stronger association in T1D than in Non-DM women. Women with T1D who report irregular menses have increased CAC progression, compared with those with regular menses.
| Introduction |
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Differences in conventional risk factors do not explain all of the increased CAD risk associated with T1D in women, and these women lose the normal premenopausal protection against CAD (2). The reason for this loss of normal premenopausal protection against CAD is presently unknown. Ovarian dysfunction and irregular menstrual cycles have been shown to be associated with increased CAD risk in nondiabetic women (8) and are more common in women with T1D than women without diabetes (9, 10, 11). Previous studies have shown that women with T1D who have abnormal menstrual cycles and no residual insulin secretion have reduced estrogen and estradiol levels, in addition to low levels of LH, suggesting suppression of ovarian function (12). A recent study of angiographic CAD among premenopausal women found a more than 7-fold increase in CAD associated with hypoestrogenemia due to hypothalamic suppression of ovarian function (13). Given this evidence, it is possible that at least part of the increased risk of CAD in women with T1D may be related to hypoestrogenemia.
The use of exogenous estrogen may have beneficial effects on CAD risk in premenopausal women with low estrogen. However, there has been some concern that oral contraceptives may not be appropriate for use in women with T1D or other metabolic problems (14, 15) because there is some evidence they may increase insulin resistance (16), lipoprotein abnormalities, and microalbuminuria (17). Several studies have supported the use of oral contraceptives in T1D, showing that the use of oral contraceptives does not appear to affect glycemic control or insulin resistance (14, 18, 19). The American College of Obstetrics and Gynecology practice bulletin states that hormonal contraception in diabetes should be limited to nonsmoking women younger than 35 yr old with no hypertension or vascular disease, including retinopathy and nephropathy (20). As a result, women with T1D are less likely to use hormonal birth control than nondiabetic women (10).
It is now increasingly recognized that women with T1D have more menstrual dysfunction than women without diabetes (9, 10, 11, 21, 22, 23), and alterations in menstrual function and reproductive hormone levels have been shown to be associated with increased CAD risk in nondiabetic women (8, 24, 25). However, to our knowledge no studies have yet examined whether menstrual dysfunction is associated with CAD in women with T1D, and the long-term relationship between exogenous hormone use and CAD in these women is poorly understood. Several small studies reported a protective effect of oral contraceptive use on CAD risk in women with T1D (26, 27), but the effect of oral contraceptive use or other hormonal contraceptives on long-term risk of CAD in women with T1D needs further study. The purpose of this study was to determine whether menstrual irregularity is associated with increased coronary artery calcium (CAC) progression in women with and without T1D, whether HBC therapy is associated with decreased CAC progression in women with and without T1D, and whether these relationships differ by diabetes status.
| Subjects and Methods |
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A total of 1420 people, including 737 women, were enrolled in the Coronary Artery Calcification in Type 1 Diabetes study. The purpose of this study was to determine which factors predict a significant increase in coronary artery calcium or the development of clinical CAD in people with T1D. An additional study goal was to investigate potential explanations for the relatively greater impact of diabetes on CAD risk in women than men. One female participant and three male participants did not meet the inclusion criteria and were dropped from the study as previously described (28). Of the 736 female study participants, 612 completed two visits with coronary calcium measurements. Study participants were 293 women with T1D and 319 women who reported never having been diagnosed with diabetes, including gestational diabetes, and were recruited from among the spouses and friends of the participants with diabetes. All participants were 19–55 yr of age and had no history of myocardial infarction, coronary artery bypass surgery, or angioplasty. Inclusion criteria for participants with diabetes were diagnosis before the age of 30 yr or positive antibodies or a clinical course consistent with T1D; insulin therapy within 1 yr of diagnosis; and long-standing diabetes (mean duration 24 yr, range 4–52 yr). Despite the use of these entrance criteria, it is possible that some women had type 2 diabetes. All participants provided informed consent, and the study protocol was approved by the Colorado Combined Institutional Review Board.
Examination and laboratory measurements
Participants completed a baseline examination between March 2000 and April 2002, and a follow-up examination between December of 2002 and March of 2005. At each visit, participants came to the clinic after a 12-h fast for blood collection, anthropometric measurements, and examination as previously described (6). Hypertension was defined as a blood pressure 140/90 mm Hg or greater or current antihypertensive treatment as outlined in the National Cholesterol Education Program Adult Treatment Panel III final report (29). Participants self-reported their smoking history and reproductive history.
CAC measurement by electron beam computed tomography (EBCT)
At each visit, two sets of high-resolution, noncontrast, contiguous 3-mm tomographic images were acquired at 100-msec exposure on an Imatron C-150XLP EBCT scanner (Imatron, San Francisco, CA) as previously described (6). The two sets of scans were acquired within 5 min.
Hormonal birth control use
Women were asked a single question regarding use of hormonal methods of birth control, which asked them whether they had ever used oral contraceptives, Norplant, or Depo-Provera. It is therefore not possible to separate out these methods. However, this study is ongoing and women are now being asked about their lifetime history of use of each of these methods separately. Based on the 506 women who have returned for an additional visit to date, the use of Norplant was rare, with only one woman reporting the use of Norplant and never having used oral contraceptives. Similarly, the use of Depo-Provera was uncommon, with only six women reporting the use of Depo-Provera and no use of oral contraceptives. Among the 506 women, the use of oral contraceptives before the baseline visit when assessed separately from other hormonal birth control methods was reported in 422 of women overall (83.4%): 197 of the 245 women with T1D (80.4%) and 225 of the 261 women without diabetes (86.2%).
Statistical analysis
Continuous variables were examined for a linear relationship with CAC progression. CAC scores were positively skewed, with a high frequency of zero values. Coronary calcium interpolated volume from each scan was square root transformed to reduce the variance across coronary calcium scores (30), and the square root transformed volumes were averaged for each visit. The difference between mean square root transformed coronary calcium volumes was calculated from the baseline visit to the follow-up visit. Progression of coronary calcium was defined as an increase in square root transformed coronary calcium volume 2.5 or greater over the course of the two visits (30) or development of clinical CAD between the baseline and follow-up visit (myocardial infarction, coronary artery bypass graft surgery, or angioplasty). Variables of interest were compared between women with and without T1D using a two-sample t test for continuous variables and a
2 test for categorical variables.
The change in square root transformed coronary artery calcium volume over the follow-up period was examined using linear regression. Logistic regression was used to examine the age-adjusted association between variables of interest and progression of CAC. All statistical tests were two sided, with P < 0.05 considered statistically significant.
| Results |
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Menstrual history differed significantly by diabetes status, with women with T1D reporting significantly later menarche, longer menstrual cycles, more irregular menstrual periods, and more amenorrhea. Altogether, 30.5% of women with T1D reported menstrual dysfunction (irregular periods and/or amenorrhea), compared with 19.0% of nondiabetic women (P < 0.001).
The proportion of women who had ever been pregnant did not differ by diabetes status, and neither did the total number of pregnancies reported. However, the number of live births was significantly lower among women with T1D. The percentage of women who were postmenopausal by self-report did not differ by diabetes status.
Characteristics of the study participants by diabetes and history of hormonal birth control (BC) use is shown in Table 2
. Among women with T1D, those who had never used BC were older and had longer diabetes duration, were more likely to be hypertensive, and had a later average age at menarche. In addition, women with T1D who had never used BC had higher CAC scores at baseline, a greater change in coronary calcium volume, and were more likely to have significant progression of CAC than women with T1D who had used BC. The only significant difference among women without diabetes by BC status was a higher number of total pregnancies and live births among never BC users than among BC users.
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| Discussion |
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Irregular menstrual periods were associated with increased progression of CAC only among women with T1D in this study. To our knowledge, no prior studies have reported on an association of irregular menstrual periods with CAD among women with T1D. However, the Nurses Health Study reported that in their cohort irregular and very irregular menstrual periods were associated with increased risk of fatal and nonfatal CAD (8). Irregular and long menstrual cycles are indicative of underlying disturbances of the reproductive axis, and sex hormones have both direct and indirect effects on the vasculature. Irregular and anovulatory cycles are a marker of polycystic ovary syndrome (PCOS), an endocrine condition associated with elevated testosterone levels and obesity.
Elevated androgen levels are associated with increased CAD risk factors, although prospective mortality studies have not demonstrated an increased risk of fatal CAD. Androgens affect the vasculature through increasing proliferation of smooth muscle cells and adhesion molecules. Whereas menstrual cycle irregularity is a common finding in women with T1D, reproductive hormone levels associated with irregular, long, or anovulatory cycles in these women have not been well characterized. PCOS and elevated androgen levels have been reported to be common among women with T1D, with PCOS reported in 19% of women with T1D, compared with an estimated 6% of women in the general population.
Amenorrhea in women with T1D is associated with low levels of estrogen, suggesting suppression of ovarian function (12, 32). It appears that this may be due to disturbances in the GnRH pulse generator rather than pituitary insufficiency because stimulated gonadotropin levels are normal in amenorrheic women with T1D (33). In a study of amenorrheic vs. normally menstruating women with T1D, la Marca et al. (33) found that 24-h cortisol levels were elevated, and LH, FSH, and estradiol were lower in women with amenorrhea than normally menstruating women. This suggests that chronic stress could increase cortisol releasing hormone, leading to inhibition of GnRH secretion and hypogonadotrophic amenorrhea. Low estrogen levels are associated with increased angiographic coronary artery disease (13), and it has been demonstrated that estrogen increases nitric oxide uptake by the endothelium and also has effects on lipids, which can inhibit the formation of fatty streaks and thereby prevent the development of atherosclerosis (34, 35).
Evidence from primate animal studies demonstrates that combination oral contraceptives protect against atherosclerosis in female monkeys with stress-induced estrogen deficiency, which suggests a possible mechanism for a protective effect of oral contraceptive use in women with T1D (36), who are at risk of hypoestrogenism (32, 33). Furthermore, premenopausal stress was shown to increase atherosclerosis in postmenopausal female monkeys, and intake of oral contraceptives during the premenopausal period ameliorated the effect of stress on postmenopausal atherosclerosis (37), which is consistent with the theory that earlier exposure to estrogen can prevent future development of coronary artery disease.
The results from this study also confirm prior reports (10) that women with T1D, when compared with nondiabetic women, are significantly less likely to use hormonal birth control and more likely to experience menstrual dysfunction, including irregular periods, amenorrhea, and long menstrual cycles. In addition, we found that women with T1D experienced later menarche (10, 38).
A limitation of this study is that the use of hormonal birth control was assessed in a single question regarding use of oral contraceptives, Depo-Provera, and Norplant. As described in Subjects and Methods, the use of Norplant and Depo-Provera by themselves are rare in this cohort. As a result, whereas there may be some misclassification, the main hormonal birth control method used by women in this cohort is oral contraceptives. The effect seen in this study would be biased in the direction of the null if some users of progestin are misclassified as oral contraceptive users.
In conclusion, the results of this study suggest that hormonal birth control therapy may be associated with a reduction in the development of atherosclerosis in all women, and the strength of this association may be greater in women with T1D. This finding is important because women with T1D are at increased risk for CAD and may also be more likely to have estrogen deficiency, menstrual dysfunction, elevated androgens, and early menopause. In addition, our data also suggest that hormonal birth control use in premenopausal women may protect against the development of fatty streaks, thus reducing the development of atherosclerosis and calcified plaque in the coronary arteries later in life.
| Acknowledgments |
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| Footnotes |
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Disclosure Statement: J.K.S.-B., D.D., L.G.O., J.E.H., G.L.K., and M.R. have nothing to disclose. J.E. is a current shareholder and previously employed by Colorado Heart Imaging, LLC, owner of the EBCT scanner.
First Published Online March 18, 2008
Abbreviations: BC, Birth control; CAC, coronary artery calcium; CAD, coronary artery disease; EBCT, electron beam computed tomography; HDL, high-density lipoprotein; LDL, low-density lipoprotein; PCOS, polycystic ovary syndrome; T1D, type 1 diabetes.
Received September 10, 2007.
Accepted March 6, 2008.
| References |
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