1 Department of Epidemiology and Preventive Medicine, University of California, Davis, CA.
2 Division of Research, Kaiser Permanente, Oakland, CA.
3 Division of Epidemiology, Stanford University, Palo Alto, CA.
4 School of Medicine, University of Pittsburgh, Pittsburgh, PA.
5 Department of Family Medicine, New Jersey Medical School, Newark, NJ.
6 School of Nursing, University of Michigan, Ann Arbor, MI.
7 New England Research Institute, Watertown, MA.
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ABSTRACT |
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ethnic groups; menopause; risk factors; smoking; social class; symptoms and general pathology
Abbreviations: SWAN, Study of Women's Health across the Nation.
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INTRODUCTION |
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In the present study, we investigated the relation of sociodemographic and lifestyle factors to a number of specific symptoms or conditions in a large, multiethnic, community-based sample of women from across the United States who participated in the first phase of the Study of Women's Health across the Nation (SWAN). We hypothesized that: 1) vasomotor and other estrogen-related symptoms would be more frequently associated with factors that result in decreased production of estrogen, such as surgical menopause, smoking, reduced body mass, and physical activity; 2) prevalence of non-estrogen-related symptoms would increase with age, independent of menopausal status; and 3) factors resulting in physiologic, economic, or social stress (lower education, being unmarried, difficulty paying for basics, and unemployment) would be associated with increased symptomatology but that the prevalence of specific symptoms would differ by race/ethnicity.
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MATERIALS AND METHODS |
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Data collection
Ascertainment of symptoms. Since the cross-sectional survey had to be brief, the presence of vasomotor, psychologic, and physical symptoms during the previous 2 weeks was determined from self-reported (yes/no) responses to closed-ended questions. Most interviews were computer-assisted telephone interviews, with about half being in-person at two sites. The specific symptoms included were based primarily on previous epidemiologic work on Caucasian women (57
) and included the following: difficulty sleeping, night sweats, headaches, hot flushes or flashes, forgetfulness, vaginal dryness, leaking urine, feeling tense or nervous, feeling blue or depressed, and irritability or grouchiness. In addition, symptoms such as stiffness or soreness in joints, neck, or shoulders and heart pounding or racing were included, based on previous anthropologic work in the different race/ethnic groups (8
, 9
). Symptoms thought to be associated with menopause, such as hot flashes, night sweats, and vaginal dryness, were interspersed with other symptoms to minimize bias from stereotypic thinking about menopause (10
). The relation of demographic and lifestyle variables to the psychologic symptoms is addressed elsewhere (L. H. Powell et al., Rush Presbyterian-St. Luke's Medical Center, unpublished manuscript), while the relations to physical symptoms are addressed here.
Assessment of independent variables. Independent variables of interest were self-reported current status related to demographic factors (age, race/ethnicity, educational attainment, employment, marital status, number of children, and ability to pay for basics), lifestyle factors (smoking, physical activity), height and weight, and menopausal status.
Race/ethnicity was self-defined as Black or African American, non-Hispanic Caucasian, Chinese or Chinese American, Japanese or Japanese American, or Hispanic (Central American, Cuban or Cuban American, Dominican, Mexican or Mexican American, Puerto Rican, South American or Spanish, or other Hispanic). In addition, respondents could specify a race/ethnicity other than the defined categories or indicate "mixed" or no primary affiliation. Since most extant literature is based on non-Hispanic Caucasians, this was the reference group. Questions about smoking were modified from those of the American Thoracic Society (11). Physical activity was assessed with one question about activity level relative to other women of the respondent's age. The body mass index was calculated from self-reported height and weight and equals weight (kg)/height (m)2.
Menopausal status was based on menstrual characteristics as: surgical, indicating menses had stopped as a result of hysterectomy and/or oophorectomy (thus not necessarily representing cessation of hormonal cycling); postmenopausal, indicating menses had stopped for at least 12 months without surgery; late perimenopausal, indicating menses had occurred in the past 12 months but not in the last 3 months; early perimenopausal, indicating menses had occurred in the past 3 months but had become less predictable; and premenopausal, indicating menses had occurred in the past 3 months with no decrease in predictability. Women whose menstrual periods had stopped because of medication, radiotherapy, pregnancy or lactation, or extreme weight change (n = 311), who reported use of exogenous female hormones in the past 3 months (since such use might reflect greater symptom prevalence or reduced symptom reporting and thus be uninterpretable, n = 1,635), or who reported their race/ethnicity as mixed/other (since this was a very non-homogeneous group, n = 1,694) were excluded, for a total of 12,425 included in the present analyses.
Data analyses
Crude prevalence odds ratios for the association between the selected characteristics and each symptom were computed. Multiple logistic regression was used to adjust prevalence odds ratios simultaneously for site and demographic, lifestyle, and reproductive characteristics (12). As a result of factor analyses (13
), we combined hot flashes and night sweats into one outcome variable of hot flashes and/or night sweats. The odds ratios for the symptoms "difficulty sleeping," "forgetful," and "heart pounding or racing" were also adjusted for reporting irritability, feeling tense, or feeling anxious or depressed. Initial exploratory adjustment for diagnosis or treatment of arthritis was made for the symptom "stiffness or soreness in joints, neck, or shoulders," but this did not modify the results. Exploratory adjustment for language in which the interview was conducted, as an indicator of acculturation, also did not modify the results.
Parity was treated as a continuous variable. Four-year age groups and body mass index (14) were treated as categorical variables, since they were not linearly related to the prevalence of most of the symptoms. All categorical variables were treated as dummy variables in the logistic regression, thus assuming no particular ordering. Goodness-of-fit of models was tested by the Hosmer and Lemeshow procedure (15
). Because sites were not randomly selected and because sampling procedures varied by site to accommodate the difficulties in attaining adequate numbers of each racial/ethnic minority (i.e., formal representative sampling procedures were not exclusively used at two sites), use of estimation procedures based on formal sampling methods was inappropriate. The variance estimates used in the confidence intervals shown here were thus based on simple random sampling, but they should be interpreted with caution for these reasons.
Interactions of race/ethnicity or menstrual status with the association of each factor and symptom were first examined by stratifying on race/ethnicity or menstrual status to determine if the stratum-specific natural logarithms of the odds ratios differed from each other or from the unstratified natural logarithm odds ratio by more than two times the standard error for the unstratified effect. If so, the statistical significance of interaction terms was examined in the multiple logistic regression model.
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RESULTS |
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Multivariate adjusted associations of risk factors to symptoms
Age. After adjustment for the other covariates in table 1, vasomotor symptoms and urine leakage were not related to age in postmenopausal and late perimenopausal women (data not shown).
Menstrual status. Menstrual status had the largest adjusted prevalence odds ratios of any risk factor for most symptoms, particularly vasomotor (table 3). All symptoms were more frequent in women who were not premenopausal. Vasomotor symptoms were particularly frequent in women who were in the late perimenopause, although the numbers in this category were relatively small.
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Race/ethnicity. All symptoms, except heart pounding and forgetfulness, were reported less frequently by Japanese and Chinese women compared with non-Hispanic Caucasians. This finding persisted after adjustment for language as a measure of acculturation (data not shown). Urine leakage and difficulty sleeping were reported significantly less often, but vasomotor symptoms and vaginal dryness were reported significantly more frequently by African-American than by Caucasian women. Hispanic women reported urine leakage, vaginal dryness, heart pounding or racing, and forgetfulness more frequently than did non-Hispanic Caucasian women. All minority ethnic groups reported difficulty sleeping significantly less frequently than did Caucasians after adjusting for other covariates. No marked interaction of race/ethnicity with prevalence odds ratios for risk factors and symptoms was observed.
Body mass index. Hot flashes or night sweats, urine leakage, and stiffness or soreness in joints, neck, or shoulders were reported more frequently in women with a body mass index of 27 kg/m2 or greater compared with women with a body mass index of 1926.9 kg/m2 (or less). This relation was particularly marked for urine leakage, for which prevalence increased more than twofold for women with a body mass index of 32 kg/m2 or greater. However, hot flashes or night sweats were not associated with an increased body mass index in postmenopausal and late peri-menopausal women (data not shown).
Smoking. Past smoking and current smoking were related to prevalence of most symptoms, except vaginal dryness and forgetfulness (the latter being positively related only to past smoking). No clear trends with amount currently smoked were observed.
Physical activity. All symptoms (particularly stiffness or soreness, heart pounding or racing, forgetfulness, and difficulty sleeping) were more frequent among women who reported getting less physical activity compared with women who reported getting much more or somewhat more physical activity than women of the same age. A trend appeared of increasing prevalence of these symptoms with decreasing physical activity.
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DISCUSSION |
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Despite the use of quite varied methodologies, in numerous cross-sectional studies of clinical, psychosocial, and sociodemographic factors associated with the menopausal transition in Caucasian women, a few major findings have emerged. First, vasomotor symptoms, such as hot flashes or flushes and night sweats, are unequivocally linked to hormonal changes (1618
). Longitudinal studies have largely confirmed the relation between vasomotor symptoms and the climacteric (6
, 18
21
), and reports of vasomotor symptoms at peri- or postmenopause have been found to be inversely related to the level of serum estrogens (6
, 16
). Menopause and reduction in endogenous estrogen levels result in atrophic changes of epithelial tissues including the skin and vaginal wall (22
). Other symptoms, such as sleep difficulties, are less consistently associated with menopausal status (23
27
). Further, a subset of women with low socioeconomic status who experience difficulties with personal and social functioning during the climacteric may report more symptoms (17
).
Menstrual status and age
The results from our study indicate that over half of late perimenopausal women report hot flashes or night sweats. This estimate is in agreement with other studies showing that the occurrence of hot flashes increases with irregularity in menses, peaking at 50 percent just prior to menopause, and later declining in the postmenopause (28). The prevalence of hot flashes in perimenopausal women of Anglo-European origin is reported to be 5085 percent (25
, 27
).
The prevalence of vaginal dryness in the present study was 13.1 percent, in agreement with several studies (2932
). However, in a cross-sectional study of 5,990 Swedish women, aged 4662 years, the prevalence of vaginal dryness was 21 percent, with prevalence increasing with age to about 34 percent in 62-year-old women (33
). Wilbur et al. (16
) noted a higher prevalence (29 percent in women aged 3569 years), with the wider age range than our population possibly accounting for the higher prevalence. Another limitation of previous work, however, is using age as a surrogate for menstrual status, whereas the present study used reported bleeding patterns.
Socioeconomic status
In the present study, lower educational attainment and greater difficulty paying for basics were related to increased symptom prevalence. In addition, lack of full-time employment was associated with heart pounding or racing, forgetfulness, and difficulty sleeping. These findings are consistent with those of a number of others (16, 24
, 34
, 35
).
Race/ethnicity
The prevalence of vasomotor symptoms in developed countries in largely Caucasian populations has previously been examined in cross-sectional (22, 25
, 32
, 33
, 36
) and prospective (20
, 21
) studies, with considerable variability in results. The finding in the present study that more African-American women reported hot flashes or night sweats than Caucasian women (37 percent vs. 24 percent) is of interest. In a study of Caucasian and African-American women from a population-based study of reproductive cancers, 71 percent of participants reported experiencing hot flashes at menopause, with no racial differences in prevalence (34
). Our finding of increased reporting of vaginal dryness in African-American women also differs from recent unadjusted findings by Wilbur et al. (16
), which also indicate an increased risk of urine leakage in African-American women, while we found a reduced prevalence of this symptom in this group compared with Caucasians. Also of interest in the present study, Hispanic women reported the highest prevalence of vaginal dryness. Asian women (9
, 36
39
) report fewer hot flashes than do Caucasian women. Because of simultaneous adjustment of multiple variables in the present study, differences among race/ethnic groups in these other variables (e.g., body mass index or smoking) do not account for differences in symptom reporting among the groups.
Body mass index
In the present study, women with a body mass index of at least 32 kg/m2 had a greater prevalence of hot flashes or night sweats (43.8 percent) than did those having a body mass index of less than 19 kg/m2 (30.6 percent). A higher body mass index has been associated with increased symptom reporting during the menopausal transition in one study (40) and with fewer hot flashes in other studies (34
, 41
, 42
). Since adrenal androgens are converted to estrogen in adipose tissue (43
), and since vasomotor symptoms are thought to be related to reduced estrogen levels, a lower prevalence of vasomotor symptoms is expected in heavier women. The reasons for the present findings are unclear. Possibly the rate (and steepness) of the decline in or the widely fluctuating levels of estradiol (44
) may affect symptoms more than absolute levels (which would be associated with body weight). Differences in study design (cross-sectional vs. prospective), sample size, methods in ascertaining body mass index (self-report vs. direct measurement), and simultaneous control of covariates (especially smoking) may also account for discrepant findings.
Smoking
Past smoking and current smoking were positively associated in the present study with prevalence of vasomotor symptoms, in agreement with most but not all (34) others (45
48
). Women who smoke would be expected to have a higher prevalence of vasomotor symptoms because of the antiestrogenic effects of smoking (49
51
); however, the lack of association of smoking with vaginal dryness is thus unexpected, suggesting that other factors may be more important in the occurrence of vaginal dryness. We did observe that vaginal dryness was significantly less often reported among never married, widowed, or divorced women compared with married women, suggesting that opportunity for sexual activity may be related to reporting of vaginal dryness.
Physical activity
In contrast to the present study, previous cross-sectional surveys have generally failed to find any association between physical activity and vasomotor symptoms (46, 52
55
). One study reported a lower prevalence of hot flashes among regularly active perimenopausal women compared with population controls whose activity level was not determined (30
). The inconsistency between the present findings and those of previous investigations may be due, in part, to the assessment method. The present study asked about the respondent's perception of activity level but not what she actually did. This may predispose women who are having more symptoms to perceive themselves as less active than their peers. Alternatively, previous studies, with more limited sample sizes, may not have had the statistical power of the present study to detect significant relations between activity and vasomotor symptoms. Most cross-sectional surveys have observed fewer somatic symptoms (52
) and better health status (53
, 55
) in active women compared with sedentary women. Given the cross-sectional design of all of these studies, it is not possible to determine whether women feel better because they are active or are less active because they are symptomatic.
Limitations of the present study
The present study was cross-sectional. Thus, for certain variables, such as body mass index and physical activity, we could not be certain that the factor actually preceded and thus predisposed to the occurrence of symptoms. However, a number of the factors (e.g., education, parity, and smoking) were unlikely to have changed recently for most women and thus were likely to have preceded symptom reporting. Nonetheless, the temporal sequence of these associations will be better established in the next phase of SWAN, the longitudinal study.
Another limitation is self-reporting, particularly of symptoms, body mass index, and menstrual status. The use of standard questions for these items enhances the comparability of these results with those of prior studies. Again, however, these assessments will be improved in longitudinal assessment and correlation with biologic measures of endocrine status in the next phase of SWAN.
A third limitation is the varied sampling methods used among sites, necessitated by difficulties in achieving needed sample size of minority populations, making use of formal estimation procedures inappropriate. Thus, the present confidence intervals should be interpreted with caution.
A final limitation is the potential for inadequate detail on variables of interest and inadequate control of potential confounding factors. In this limited interview, it was not possible to examine all such potential factors. In particular, more detailed questions could not be asked about both symptoms (e.g., nature of headaches and difficulty with sleep) and additional risk factors, such as diet, nature of occupation, income, pack-years of smoking, and nature and intensity of physical activity. Thus, uncontrolled confounding and insufficient detail are potential limitations that will be better addressed in the SWAN longitudinal study.
Strengths of the present study
This is the first study to have large numbers of women at various stages of the menopausal transition and from five race/ethnic groups. Women were selected to be generally representative of their racial/ethnic group in their geographic area and came from several geographic areas in the United States. Thus, these results should apply to a large segment of women in this age group in this country. In addition, the use of standardized methods of data collection over several geographic areas is an important strength. Finally, the effects of each variable were examined while controlling for many others.
Conclusions
The results of the SWAN cross-sectional survey indicate that a number of potentially modifiable factors affect symptom reporting. Thus, for women for whom medical treatment is contraindicated, undesired, or not tolerated, alternatives may be offered in lifestyle changes. In particular, smoking cessation was associated with lower prevalence than in current smokers of vasomotor symptoms and difficulty sleeping. Increased physical activity was associated with lower prevalence of virtually all symptoms. Overweight was associated with hot flashes/night sweats, urine leakage, and stiffness or soreness. All of these factors are, of course, also associated with a number of other adverse health effects. Our results also provide guidance to health care providers in assessing symptoms by increasing their sensitivity to differences in symptom-reporting patterns by race/ethnicity and menstrual status. Importantly, our results also show that most indicators of low socioeconomic status, particularly low educational level and difficulty paying for basics, were associated with significantly increased reporting of almost all symptoms.
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ACKNOWLEDGMENTS |
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Participating institutions and principal staff were as follows. Clinical Centers: University of Michigan, Ann Arbor (grant U01 NR04061; MaryFran Sowers, Principal Investigator); Massachusetts General Hospital, Boston (grant U01 AG12531; Robert Neer, Principal Investigator (19941999), Joel Finkelstein, Principal Investigator (current)); Rush University, Rush-Presbyterian-St. Luke's Medical Center, Chicago (grant U01 AG12505; Lynda Powell, Principal Investigator); University of California, Davis/Kaiser (grant U01 AG12554; Ellen Gold, Principal Investigator); University of California, Los Angeles (grant U01 A12539; Gail Greendale, Principal Investigator); University of Medicine and Dentistry-New Jersey Medical School, Newark (grant U01 AG12535; Gerson Weiss, Principal Investigator); and the University of Pittsburgh, Pittsburgh (grant U01 AG12546; Karen Matthews, Principal Investigator). Central Laboratory: University of Michigan, Ann Arbor (grant U01 AG12495; Central Ligand Assay Satellite Services, Rees Midgley, Principal Investigator). Coordinating Center: New England Research Institutes, Watertown, Massachusetts (grant U01 AG12553; Sonja McKinlay, Principal Investigator). Project Officers: Taylor Harden, Carol Hudgings, Marcia Ory, and Sheryl Sherman. Steering Committee Chair: Christopher Gallagher (19941996); Jennifer L. Kelsey (currently).
The authors thank the study staff at each site and all of the women who participated in SWAN. They also gratefully acknowledge the statistical programming assistance of Yan Luo and Marianne O'Neill Rasor.
The manuscript was reviewed by the Publications and Presentations Committee of SWAN and has its endorsement.
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NOTES |
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REFERENCES |
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