Objective
Many women with urinary incontinence (UI) have symptoms that continue over many years; however, virtually nothing is known about factors that are associated with persistent UI.
Study Design
We studied 36,843 participants of the Nurses’ Health Study, aged 54-79 years at baseline for the UI study, who provided UI information on biennial questionnaires from 2000 through 2008; follow-up in the Nurses’ Health Study is 90%. In total, 18,347 women had “persistent UI,” defined as urine leakage ≥1/mo reported on all 5 biennial questionnaires during this 8-year period; 18,496 women had no UI during this period. Using multivariable-adjusted logistic regression, we estimated odds ratios (ORs) of persistent UI vs no UI across various demographic, lifestyle, and health-related factors, which were derived from reports in 2000.
Results
Increasing age group, white race, greater parity, greater body mass index (BMI), and lower physical activity levels were each associated with greater odds of persistent UI, as were several health-related factors (ie, stroke, type 2 diabetes, and hysterectomy). Associations with persistent UI were particularly strong for increasing age group ( P trend < .0001; OR, 2.75; 95% confidence interval [CI], 2.54–2.98 comparing women aged ≥75 vs <60 years) and greater BMI ( P trend < .0001; OR, 3.14; 95% CI, 2.95–3.33 comparing women with BMI ≥30 vs <25 kg/m 2 ); moreover, black women had much lower odds of persistent UI compared to white women (OR, 0.27; 95% CI, 0.21–0.34).
Conclusion
Factors associated with persistent UI were generally consistent with those identified in previous studies of UI over shorter time periods; however, older age, white race, and obesity were particularly strongly related to persistent UI.
Urinary incontinence (UI) is a common condition among women, which can lead to substantial reductions in quality of life for affected individuals. In addition, UI is responsible for increased financial burdens on individuals as well as the health care system. Numerous epidemiologic studies have identified factors associated with prevalent and incident UI, and have offered insight into the etiology of this condition and suggested possible strategies for mitigating UI. However, previous epidemiologic research has focused largely on UI assessment at 1 or 2 points in time, including analyses in the Nurses’ Health Study, despite clinical observations indicating that UI is a complex, dynamic condition. Longitudinal studies involving a larger number of repeated UI assessments over time have begun to yield important information regarding the natural history of UI, although there is still relatively little known about specific risk factors for UI that persists over many years. Thus, we evaluated factors associated with persistent UI over 8 years of follow-up among women participating in the Nurses’ Health Study–in whom we have collected UI information on repeated biennial questionnaires.
Materials and Methods
Study population
The Nurses’ Health Study was initiated in 1976, when 121,700 female nurses, aged 30-55 years, responded to a mailed questionnaire on their medical history and lifestyle; this information is updated with similar questionnaires every 2 years. Questions about UI were included on the questionnaires in 2000, 2002, 2004, 2006, and 2008; to date, the follow-up rate is approximately 90%. The institutional review board of Brigham and Women’s Hospital approved this study, and informed consent was implied by return of the questionnaires.
Measurement of UI
On the biennial questionnaires from 2000 through 2008, participants were asked, “During the last 12 months, how often have you leaked or lost control of your urine?” Response options were: never, less than once per month, once per month, 2-3 times per month, about once per week, and almost every day. A reliability study among a subgroup of the nurses demonstrated high reproducibility of responses to this question. Cases were classified as “any UI” if women reported leaking urine at least once per month, and as “frequent UI” if women reported leaking at least once per week. UI cases were classified as “persistent” if women reported UI on all questionnaires from 2000 through 2008; these cases were the focus of the analyses presented here.
Measurement of exposures
The biennial questionnaires included information on a wide variety of demographic, health, and lifestyle factors, including age, race, height and weight, reproductive history, alcohol intake, smoking, physical activity, postmenopausal hormone use, vascular conditions, and hysterectomy. Participants reported their race and ethnicity on the 2004 questionnaire, and we classified women as white, black, or Asian if they identified with one of these racial groups. Height was reported on the initial questionnaire, and weight, number of births, smoking habits, postmenopausal hormone use, and hysterectomy status were reported on most of the biennial questionnaires. Information on physical activity was collected in 1986, 1988, 1992, and every 2 years thereafter; specifically, participants reported the number of hours spent on various leisure activities (eg, walking, running) during the past year, and total energy expenditure was calculated in metabolic-equivalent hours per week, which has been previously described in detail. In addition, participants reported diagnoses of stroke, myocardial infarction, and type 2 diabetes on biennial questionnaires.
Population for analysis
Of the original 121,700 Nurses’ Health Study participants, 108,673 were alive at UI baseline (ie, return date of the 2000 questionnaire) and 84,013 of those women responded to UI questions on that questionnaire. Among participants with baseline information on UI, we included 75,515 women in our analyses who answered UI questions on at least 2 additional questionnaires during the period 2002 through 2008 (ie, 90% of those who answered UI questions at baseline). Of women in our analytic sample, 77% (n = 58,260) provided UI information on all 5 questionnaires from 2000 through 2008; for women missing UI information on 1 or 2 follow-up questionnaires, we imputed their UI status from the most recent report (all findings were nearly identical in alternate analyses using only women with complete information on all 5 questionnaires).
For these analyses of persistent UI, we included 2 groups of participants: 18,347 women who reported UI consistently on biennial questionnaires from 2000 through 2008, and 18,496 women who reported having no UI on any of these questionnaires. For analyses of persistent frequent UI, we included 7843 women who reported frequent UI consistently on questionnaires during 2000 through 2008, and the 18,496 women who reported no UI on these questionnaires.
Statistical analysis
To evaluate factors related to persistent UI, we used multivariable-adjusted logistic regression to estimate odds ratios (OR) for any UI and frequent UI vs no UI during follow-up across categories of the following variables: age (<60, 60-64, 65-69, 70-74, ≥75), race (white, black, Asian), body mass index (BMI) (<25, 25-29.9, ≥30 kg/m 2 ), parity (0, 1-2, ≥3 births), alcohol intake (none, 1-14, ≥15 g/d), smoking status (never, past, current), physical activity (metabolic-equivalent h/wk in tertiles), postmenopausal hormone use (never, past, current), history of stroke (yes, no), history of myocardial infarction (yes, no), history of type 2 diabetes (yes, no), and prior hysterectomy (yes, no). The status of these factors was determined based on the participant’s report at baseline (ie, on the 2000 questionnaire), except that physical activity was defined using an average of all available reports through baseline to represent long-term physical activity. We calculated 95% confidence intervals (CIs) for all estimates, and evaluated linear tests of trend for ordinal variables.
In secondary analyses, we examined the association between BMI and persistent UI after excluding women who were underweight (ie, BMI ≤18.5 kg/m 2 ).
Results
Table 1 shows age-adjusted characteristics of our study population at the initial UI assessment in 2000, separately for women with persistent UI vs no UI during the study period. Compared to women with no UI, women with persistent UI were older, slightly more parous, and more likely to report current use of postmenopausal hormones and prior hysterectomy. In addition, women with persistent UI, on average, had higher BMI and lower physical activity levels compared to women without UI.
| Variable | Women with persistent UI a (n = 18,347) | Women with no UI a (n = 18,496) |
|---|---|---|
| Age, y, % | ||
| <60 | 19 | 27 |
| 60-64 | 20 | 23 |
| 65-69 | 22 | 21 |
| 70-74 | 22 | 17 |
| ≥75 | 17 | 12 |
| Race, % | ||
| White | 99 | 97 |
| Black | 1 | 2 |
| Asian | <1 | 1 |
| Body mass index, kg/m 2 , % | ||
| <25 | 35 | 53 |
| 25-29.9 | 35 | 33 |
| ≥30 | 30 | 14 |
| Parity, % | ||
| 0 births | 5 | 7 |
| 1-2 births | 34 | 37 |
| ≥3 births | 61 | 56 |
| Median alcohol intake, g/d (IQR) | 0.9 (0-5.8) | 1.5 (0-6.7) |
| Smoking status, % | ||
| Never | 45 | 46 |
| Past | 46 | 43 |
| Current | 9 | 11 |
| Median physical activity, MET h/wk (IQR) | 12.0 (6.0-21.4) | 14.8 (7.6-25.9) |
| Postmenopausal hormone use, % | ||
| Never | 20 | 32 |
| Past | 22 | 25 |
| Current | 58 | 43 |
| History of stroke, % | 2 | 1 |
| History of myocardial infarction, % | 4 | 3 |
| History of type 2 diabetes, % | 9 | 5 |
| Had hysterectomy, % | 46 | 34 |
In multivariable models adjusting simultaneously for all factors that we examined in relation to UI, we found multiple demographic, lifestyle, and health-related factors that were independently associated with persistent UI ( Table 2 ). For demographic factors, increasing age was highly associated with increasing odds of persistent UI ( P trend < .0001); for example, women ≥75 years of age had 3 times higher odds of persistent UI than women <60 years (OR, 2.75; 95% CI, 2.54–2.98). This association was stronger when we considered frequent UI, such that women aged ≥75 years had nearly 4 times the odds of persistent frequent UI compared to those <60 years of age ( P trend < .0001; OR, 3.56; 95% CI, 3.21–3.96). Parity was also related to modestly greater odds of persistent UI (OR, 1.58; 95% CI, 1.44–1.74 comparing women with ≥3 births vs no births) and persistent frequent UI (OR, 1.82; 95% CI, 1.59–2.07 for the same comparison). In contrast, nonwhite women had substantially lower odds of persistent UI, especially black women (OR, 0.27; 95% CI, 0.21–0.34) although reduced odds were apparent for Asian women as well (OR, 0.69; 95% CI, 0.51–0.92) compared to white women. Similar associations were found between race and persistent frequent UI (OR, 0.30; 95% CI, 0.22–0.41 for black vs white women, and OR, 0.64; 95% CI, 0.42–0.98 for Asian vs white women).
| Variable | UI at least monthly | UI at least weekly | ||
|---|---|---|---|---|
| Cases | OR (95% CI) | Cases | OR (95% CI) | |
| Age, y | ||||
| <60 | 3473 | 1.00 (ref) | 1313 | 1.00 (ref) |
| 60-64 | 3703 | 1.26 (1.18–1.35) | 1577 | 1.45 (1.33–1.60) |
| 65-69 | 4126 | 1.66 (1.55–1.78) | 1756 | 1.93 (1.76–2.12) |
| 70-74 | 3949 | 2.14 (1.99–2.30) | 1762 | 2.60 (2.36–2.87) |
| ≥75 | 3096 | 2.75 (2.54–2.98) | 1435 | 3.56 (3.21–3.96) |
| P trend < .0001 | P trend < .0001 | |||
| Race | ||||
| White | 17,787 | 1.00 (ref) | 7597 | 1.00 (ref) |
| Black | 105 | 0.27 (0.21–0.34) | 53 | 0.30 (0.22–0.41) |
| Asian | 77 | 0.69 (0.51–0.92) | 28 | 0.64 (0.42–0.98) |
| Body mass index, kg/m 2 | ||||
| <25 | 6595 | 1.00 (ref) | 2456 | 1.00 (ref) |
| 25-29 | 6394 | 1.58 (1.50–1.66) | 2716 | 1.80 (1.68–1.92) |
| ≥30 | 5358 | 3.14 (2.95–3.33) | 2671 | 4.12 (3.82–4.45) |
| P trend < .0001 | P trend < .0001 | |||
| Parity | ||||
| 0 births | 878 | 1.00 (ref) | 338 | 1.00 (ref) |
| 1-2 births | 6005 | 1.32 (1.20–1.46) | 2493 | 1.47 (1.28–1.68) |
| ≥3 births | 11,464 | 1.58 (1.44–1.74) | 5012 | 1.82 (1.59–2.07) |
| Alcohol intake, g/d | ||||
| None | 7706 | 1.00 (ref) | 3502 | 1.00 (ref) |
| 1-14 | 8553 | 1.03 (0.99–1.08) | 3482 | 0.94 (0.89–0.99) |
| ≥15 | 1523 | 1.12 (1.03–1.21) | 583 | 0.96 (0.87–1.06) |
| Smoking status | ||||
| Never | 8305 | 1.00 (ref) | 3466 | 1.00 (ref) |
| Past | 8534 | 1.06 (1.01–1.11) | 3721 | 1.12 (1.05–1.19) |
| Current | 1508 | 0.93 (0.86–1.01) | 656 | 1.03 (0.92–1.14) |
| Physical activity (in tertiles of MET h/wk) | ||||
| Low (<7.6) | 5894 | 1.00 (ref) | 2670 | 1.00 (ref) |
| Medium (7.6-17.9) | 6517 | 0.86 (0.81–0.90) | 2798 | 0.85 (0.80–0.90) |
| High (≥18.0) | 5864 | 0.73 (0.69–0.77) | 2341 | 0.71 (0.66–0.76) |
| P trend < .0001 | P trend < .0001 | |||
| Postmenopausal hormone use | ||||
| Never | 3595 | 1.00 (ref) | 1484 | 1.00 (ref) |
| Past | 3887 | 1.27 (1.20–1.36) | 1727 | 1.29 (1.19–1.39) |
| Current | 9684 | 2.06 (1.95–2.18) | 4095 | 1.90 (1.77–2.04) |
| History of stroke | 352 | 1.56 (1.29–1.89) | 175 | 1.69 (1.35–2.12) |
| History of myocardial infarction | 681 | 1.01 (0.89–1.14) | 321 | 1.03 (0.88–1.20) |
| History of type 2 diabetes | 1625 | 1.36 (1.24–1.48) | 794 | 1.42 (1.27–1.58) |
| Had hysterectomy | 8600 | 1.35 (1.29–1.41) | 3853 | 1.42 (1.34–1.51) |
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