Objective
We sought to estimate whether moderate/severe stress urinary incontinence (SUI) in middle-aged women is associated with overall lifetime physical activity (including leisure, household, outdoor, and occupational), as well as lifetime leisure (recreational), lifetime strenuous, and strenuous activity during the teen years.
Study Design
Recruitment for this case-control study was conducted in primary-care-level family medicine and gynecology clinics. A total of 1538 enrolled women ages 39-65 years underwent a Pelvic Organ Prolapse Quantification examination to assess vaginal support. Based on Incontinence Severity Index scores, cases had moderate/severe and controls had no/mild SUI. We excluded 349 with vaginal descent at/below the hymen (pelvic organ prolapse), 194 who did not return questionnaires, and 110 with insufficient activity data for analysis. In all, 213 cases were frequency matched 1:1 by age group to controls. Physical activity was measured using the Lifetime Physical Activity Questionnaire, in which women recall activity from menarche to present. We created separate multivariable logistic regression models for activity measures.
Results
SUI odds increased slightly with overall lifetime activity (odds ratio [OR], 1.20 per 70 additional metabolic equivalent of task-h/wk; 95% confidence interval [CI], 1.02–1.41), and were not associated with lifetime strenuous activity (OR, 1.11; 95% CI, 0.99–1.25). In quintile analysis of lifetime leisure activity, which demonstrated a nonlinear pattern, all quintiles incurred about half the odds of SUI compared to reference (second quintile; P = .009). Greater strenuous activity in teen years modestly increased SUI odds (OR, 1.37 per 7 additional h/wk; 95% CI, 1.09–1.71); OR, 1.75; 95% CI, 1.15–2.66 in sensitivity analysis adjusting for measurement error. The predicted probability of SUI rose linearly in women exceeding 7.5 hours of strenuous activity/wk during teen years. Teen strenuous activity had a similar effect on SUI odds when adjusted for subsequent strenuous activity during ages 21-65 years.
Conclusion
In middle-aged women, a slight increased odds of SUI was noted only after substantially increased overall lifetime physical activity. Increased lifetime leisure activity decreased and lifetime strenuous activity appeared unrelated to SUI odds. Greater strenuous activity during teen years modestly increased SUI odds.
More than one quarter of nulliparous athletes report stress urinary incontinence (SUI) while doing their activity. Even active teenagers leak urine: 80% of trampoline jumpers reported leakage while jumping. Young women exercising at higher intensities are more likely to report SUI during sports than are those whose exercise does not include repetitive impact. It is clear that young women notice SUI during strenuous activities, but whether such activity increases the odds of future SUI is not known. Indeed, in middle-aged women, regular low intensity activity is associated with lower odds of new and persistent SUI.
The teenage years may constitute a particularly vulnerable time during which strenuous activity may have a greater deleterious effect because of the musculoskeletal, hormonal, and reproductive changes occurring in young women during that time.
Understanding how lifetime physical activity impacts SUI is important: roughly 10-20% of women between ages 40-80 years report moderate or severe incontinence, and over half have symptoms of primarily SUI. Physical activity is a modifiable risk factor with the potential for both positive and negative effects on SUI. To date, studies examining this association have not assessed lifetime physical activity or included activities other than leisure.
The aims of this study were to estimate, in a population of middle-aged women without pelvic organ prolapse (POP) recruited from nontertiary care settings, whether moderate to severe SUI is associated with overall lifetime activity (including leisure, household, outdoor, and occupational), lifetime leisure activity, lifetime strenuous activity, and strenuous activity during the teen years.
Materials and Methods
Local institutional review boards approved this study. All participants completed an informed consent process.
Research nurses recruited women for this study, as well as a separate case-control study exploring physical activity and POP, from 17 primary-care-level gynecologic and family medicine clinics located across the Salt Lake Valley in Utah from Oct. 3, 2009, through Jan. 14, 2013. Women were also initially recruited from community advertising. Complete methods have been published.
We excluded women who were pregnant or within 6 months postpartum, were age <39 or >65 years, had a body mass index (BMI) <18.5 or ≥40 kg/m 2 , had prior surgical treatment for POP or urinary incontinence (UI), were not able to walk independently, had medical conditions associated with UI or low physical activity, were currently undergoing cancer treatment, and had moderate to severe urgency incontinence (score of ≥3 on the validated Incontinence Severity Index and either pure urgency incontinence, or mixed urgency predominant incontinence, based on the 3 Incontinence Questions validated tool ). We chose our inclusion age range because the physical activity questionnaire used in this study (described below) was validated in women age 39-65 years and because women in this range are both likely to have developed SUI and to maintain physical activity.
Trained research nurses performed the POP Quantification examination to assess vaginal support. Participants completed study instruments at home. An exercise science graduate student reviewed missing and improbable response with participants using an established protocol.
To assess lifetime physical activity, we used the self-administered and reliable Lifetime Physical Activity Questionnaire (LPAQ), which is designed for use in women; includes leisure (ie, recreational) activity, outdoor work, and housework; and assesses physical activity over 4 age periods: menarche to age 21 years (the “teen” epoch), 22-34, 35-50, and 51-65 years. The LPAQ is scored using metabolic equivalents of task (MET) obtained from the Compendium of Physical Activities to calculate MET-h/wk. As the LPAQ does not include occupational activity, we added the Occupation Questionnaire (OQ), a component of the Lifetime Overall Physical Activity Questionnaire.
To calculate overall lifetime physical activity, we multiplied each activity’s MET score by the reported number of h/wk, fraction of mo/y, and fraction of years lived in each age epoch, and added the average MET-h/wk calculated on the OQ. Overall leisure activity included only activities related to traditional exercise and recreation. Strenuous activities included those associated with repetitive impact and/or relatively higher intra-abdominal pressures. Vigorous activities included those with >6 MET.
The LPAQ + OQ was considered insufficient for analysis if women recorded no physical activity of any type for an entire age epoch, no leisure or household activity over the entire LPAQ, overall physical activity exceeding 168 h/wk, or exceeded 671 MET-h/wk in any age epoch.
From the initial participant pool, we excluded women with POP (vaginal descent at or below the hymen) and those whose activity questionnaires were either unreturned or of insufficient quality.
Cases had moderate/severe UI defined as a score of ≥3 on the Incontinence Severity Index (which correlates well with incontinence severity according to pad weight, bladder diary, and quality-of-life instruments) and pure or predominantly SUI according to responses on the 3 Incontinence Questions ; controls had no or mild UI defined as a score of ≤2 on the Incontinence Severity Index and had no POP. Research nurses obtaining outcome measures were masked to LPAQ + OQ results, and exercise science researchers were masked to group assignment.
The sample size of at least 175 cases and 175 controls was calculated a priori to provide 80% power at the 2-sided 5% significance level to detect an odds ratio (OR) of 0.295 for a 1-SD increase in actual physical activity, taking measurement error into account. This sample size also had 80% power at the 2-sided 5% significance level to detect the scenario in which the OR is nonlinear in quintiles of physical activity based on the control group, with an inverted U-shape represented by a distribution of cases from lowest to highest quintile of 10-30%, or more extreme. Computations used nQuery v 6.0 software (Statistical Solutions, Boston, MA).
We planned a priori to frequency match controls and cases for age, BMI, and recruitment source. However, because we recruited only 13 cases from community advertising, but 213 from primary care clinics, we excluded community participants from our final models, as low cell sizes would preclude analysis. Additionally, before beginning data analysis, we elected not to frequency match or adjust for BMI, as 2 prospective cohort studies published after the start of our study reasoned that lifetime physical activity “causes” BMI. Thus, BMI is on the direct pathway between lifetime activity and SUI and is an effect of lifetime physical activity; including BMI could eliminate the association of activity with SUI by overadjustment.
We frequency matched controls to cases 1:1 by age (39-49, 50-60, 61-65 years), and selected controls using a computerized random number generator when >1 was eligible.
We grouped physical activity variables into quintiles based on their distribution in the selected control group, assigning the second quintile as the reference such that we could investigate the potential deleterious effect of low activity. We performed logistic regression with variable selection guided by an updated directed acyclic graph, in which BMI was depicted as an intermediate variable, developed using DAGitty version 2.0 (Johannes Textor, Theoretical Biology & Bioinformatics group, University of Utrecht, Utrecht, the Netherlands). We adjusted for education and age and further adjusted for number of vaginal deliveries and hysterectomy status, based on past literature, which was permissible per the directed acyclic graph. Regression diagnostics were checked for multicolinearity and influential observations. We examined the functional form of the relationship between each physical activity variable and SUI by inspecting plots of initial regression coefficients and using the Stata multivariable fractional polynomials procedure to identify the best polynomial fit. In the event of a nonlinear, nonpolynomial pattern, such as a threshold effect, we pooled quintiles with common ORs based on the Akaike Information Criterion. As there were only 2 missing observations in the dataset, we did not perform multiple imputation. As sensitivity analyses, we reestimated ORs using simulation extrapolation, with bootstrapped standard errors to adjust for measurement error and also reestimated ORs comparing cases to controls with no UI (ie, Incontinence Severity Index score of 0).
We generally used a 5% significance level, but considered tests for individual quintiles vs the reference category to be significant if P < .01, to adjust for multiple comparisons. All statistical programming calculations were verified by a second independent research team member. Analysis was performed using SAS 9.3 (SAS Institute, Cary, NC) and the multivariable fractional polynomial and simulation extrapolation procedures in Stata 11 and 12 (StataCorp, College Station, TX).
Results
From the primary care clinics, 1538 women met initial screening criteria and were enrolled; an additional 72 were enrolled through community advertising. The participant flow for the primary care clinic population is summarized in Figure 1 . After applying exclusion criteria, there were 213 potential cases and 642 potential controls from primary care; and 13 and 31 from the community. All cases were successfully frequency matched by age group, resulting in a primary care sample of 213 cases and 213 controls, and a community sample of 13 cases and 13 controls. There were no differences in demographic characteristics between women with sufficient vs insufficient LPAQ quality ( P > .05, data not shown). Women enrolled through community advertising were of similar age, BMI, and race/ethnicity as those enrolled through primary care clinics ( P > .05, data not shown).
Participant characteristics are summarized in Table 1 . Participants had mean (SD) age of 50 (7) years. Compared to controls, SUI cases were more likely to have delivered vaginally, be overweight or obese, and to report lower health status. Among controls, the Incontinence Severity Index scores were 0 in 111 (49.1%), 1 in 58 (25.7%), and 2 in 57 (25.2%) women.
| Variable | Measure | Control (n = 226) | SUI case (n = 226) | Univariate OR (95% CI) |
|---|---|---|---|---|
| Age, y | Mean (SD) | 49.76 (7.03) | 49.69 (7.09) | NA |
| 39-49 | n | 121 | 121 | |
| 50-60 | n | 83 | 83 | |
| 61-65 | n | 22 | 22 | |
| Body mass index, kg/m 2 | Mean (SD) | 25.61 (5.11) | 27.09 (4.92) | 1.1 (1.0–1.1) |
| 18.5-24.9 | n (%) | 130 (57.52) | 95 (42.04) | 1.0 |
| 25-29.9 | n (%) | 52 (23.01) | 64 (28.32) | 1.7 (1.1–2.6) |
| 30-39.9 | n (%) | 44 (19.47) | 67 (29.65) | 2.1 (1.3–3.3) |
| Parity | Median (range) | 2 (0–8) | 2 (0–12) | 1.2 (1.0–1.3) |
| 0 | n (%) | 63 (28.00) | 39 (17.26) | 1.0 |
| 1 | n (%) | 33 (14.67) | 39 (17.26) | 1.9 (1.0–3.5) |
| 2 | n (%) | 67 (29.78) | 74 (32.74) | 1.8 (1.1–3.0) |
| ≥3 | n (%) | 62 (27.56) | 74 (32.74) | 1.9 (1.1–3.3) |
| Missing | n | 1 | 0 | |
| No. of vaginal deliveries | Median (range) | 1 (0–8) | 2 (0–12) | 1.2 (1.1–1.3) |
| 0 | n (%) | 97 (43.11) | 62 (27.43) | 1.0 |
| 1 | n (%) | 30 (13.33) | 38 (16.81) | 2.0 (1.1–3.5) |
| 2 | n (%) | 49 (21.78) | 59 (26.11) | 1.9 (1.1–3.1) |
| ≥3 | n (%) | 49 (21.78) | 67 (29.65) | 2.1 (1.3–3.5) |
| Missing | n | 1 | 0 | |
| No. of cesarean deliveries | Median (range) | 0 (0–6) | 0 (0–6) | 0.8 (0.6–1.1) |
| 0 | n (%) | 174 (77.33) | 189 (83.63) | 1.0 |
| 1 | n (%) | 28 (12.44) | 22 (9.73) | 0.7 (0.4–1.3) |
| 2 | n (%) | 16 (7.11) | 11 (4.87) | 0.6 (0.3–1.4) |
| ≥3 | n (%) | 7 (3.11) | 4 (1.77) | 0.5 (0.2–1.8) |
| Missing | n | 1 | 0 | |
| Race | NA | |||
| Asian | n (%) | 7 (3.14) | 2 (0.90) | |
| Black/African American | n (%) | 0 (0) | 3 (1.35) | |
| Hawaiian/Pacific Islander | n (%) | 1 (0.45) | 0 (0) | |
| American Indian/Alaskan Native | n (%) | 2 (0.90) | 5 (2.25) | |
| Caucasian | n (%) | 213 (95.52) | 212 (95.50) | |
| Missing | n | 3 | 4 | |
| Ethnicity | ||||
| Non-Hispanic | n (%) | 219 (97.77) | 210 (93.33) | 1.0 |
| Hispanic | n (%) | 5 (2.23) | 15 (6.67) | 3.1 (1.1–8.8) |
| Missing | n | 2 | 1 | |
| Education | ||||
| ≤High school | n (%) | 24 (10.62) | 23 (10.18) | 1.0 |
| Some college or college graduate | n (%) | 127 (56.19) | 135 (59.73) | 1.1 (0.6–2.1) |
| Graduate/professional degree | n (%) | 75 (33.19) | 68 (30.09) | 0.9 (0.5–1.8) |
| Current smoker | n (%) | 9 (3.98) | 12 (5.31) | 1.4 (0.6–3.3) |
| Caffeine consumption | ||||
| <Once/mo | n (%) | 37 (16.37) | 35 (15.56) | 1.0 |
| Between monthly and daily | n (%) | 31 (13.72) | 33 (14.67) | 1.1 (0.6–2.2) |
| 1-3 times/d | n (%) | 138 (61.06) | 118 (52.44) | 0.9 (0.5–1.5) |
| >3 times/d | n (%) | 20 (8.85) | 39 (17.33) | 2.1 (1.0–4.2) |
| Missing | n | 0 | 1 | |
| Prior hysterectomy | n (%) | 25 (11.06) | 31 (13.78) | 1.3 (0.7–2.3) |
| Menopausal status | ||||
| Premenopausal | n (%) | 134 (61.75) | 140 (63.06) | 1.0 |
| Postmenopausal | n (%) | 83 (38.25) | 82 (36.94) | 0.9 (0.6–1.4) |
| Missing | n | 9 | 4 | |
| Medical conditions | ||||
| Seasonal allergy | n (%) | 78 (34.51) | 95 (42.04) | 1.4 (0.9–2.0) |
| Arthritis | n (%) | 36 (15.93) | 39 (17.26) | 1.1 (0.7–1.8) |
| Hypertension | n (%) | 25 (11.06) | 34 (15.04) | 1.4 (0.8–2.5) |
| Major depression | n (%) | 17 (7.52) | 26 (11.50) | 1.6 (0.8–3.0) |
| Cancer history | n (%) | 24 (10.62) | 18 (7.96) | 0.7 (0.4–1.4) |
| Sleep apnea | n (%) | 7 (3.10) | 9 (3.98) | 1.3 (0.5–3.5) |
| Diabetes | n (%) | 7 (3.10) | 6 (2.65) | 0.9 (0.3–2.6) |
| Chronic cough | n (%) | 2 (0.88) | 4 (1.77) | 2.0 (0.4–11.1) |
| Myocardial ischemia | n (%) | 1 (0.44) | 1 (0.44) | 1.0 (0.1–16.1) |
| Current no. of prescription medications | Median (range) | 1 (0–9) | 1 (0–12) | 1.1 (1.0–1.2) |
| 0 | n (%) | 76 (33.93) | 77 (34.22) | 1.0 |
| 1 | n (%) | 65 (29.02) | 50 (22.22) | 0.9 (0.7–1.3) |
| 2 | n (%) | 31 (13.8) | 46 (20.4) | 0.9 (0.6–1.3) |
| 3 | n (%) | 20 (8.93) | 13 (5.78) | 0.9 (0.6–1.5) |
| 4 | n (%) | 12 (5.36) | 16 (7.11) | 0.7 (0.4–1.2) |
| ≥5 | n (%) | 20 (8.93) | 23 (10.22) | 0.6 (0.4–0.9) |
| Missing | n | 2 | 1 | |
| Self-reported health | ||||
| Excellent | n (%) | 72 (31.86) | 49 (21.68) | 1.0 |
| Very good | n (%) | 105 (46.46) | 113 (50.00) | 1.6 (1.0–2.5) |
| Good | n (%) | 47 (20.80) | 51 (22.57) | 1.6 (0.9–2.7) |
| Fair | n (%) | 2 (0.88) | 13 (5.75) | 9.5 (2.0–44.1) |
| Sites | NA | |||
| Primary care | n (%) | 213 (94.25) | 213 (94.25) | |
| Community | n (%) | 13 (5.75) | 13 (5.75) |
Results for primary exposures
Table 2 summarizes our results.
| Physical activity measure | Age-adjusted crude OR (95% CI) | Multivariable adjusted OR (95% CI) a | Multivariable OR (95% CI) adjusted for measurement error |
|---|---|---|---|
| Primary exposures | |||
| Overall lifetime activity (U = 70 MET-h/wk b ) | 1.206 (1.029–1.413) P = .0205 | 1.196 (1.017–1.407) P = .0307 | 1.321 (1.017–1.714) P = .037 |
| Lifetime leisure activity c | P = .0070 | P = .0092 | NA |
| Quintile 1 | 0.508 (0.282–0.916) | 0.534 (0.291–0.980) | |
| Quintile 2 | 1 | 1 | |
| Quintile 3 | 0.302 (0.158–0.578) | 0.300 (0.155–0.583) | |
| Quintile 4 | 0.621 (0.351–1.097) | 0.706 (0.392–1.271) | |
| Quintile 5 | 0.592 (0.334–1.046) | 0.653 (0.363–1.175) | |
| Lifetime strenuous activity (U = 7 h/wk d ) | 1.113 (0.998–1.241) P = .0545 | 1.112 (0.994–1.244) P = .0628 | 1.161 (0.946–1.424) P = .152 |
| Teen epoch e strenuous activity (U = 7 h/wk d ) | 1.356 (1.091–1.685) P = .0061 | 1.367 (1.094–1.709) P = .0061 | 1.750 (1.153–2.657) P = .009 |
| Secondary exposures | |||
| Lifetime vigorous activity (activities with >6 MET; U = 7 h/wk f ) | 0.860 (0.517–1.428) P = .5590 | 0.891 (0.528–1.504) P = .6664 | 0.818 (0.310–2.163) P = .686 |
| Past year overall activity | 1.085 (0.864–1.362) P = .4821 | 1.072 (0.850–1.352) P = .5573 | 1.124 (0.739–1.709) P = .583 |
| Past year leisure activity (U = 35 MET-h/wk g ) | 0.806 (0.657–0.990) P = .0398 | 0.809 (0.654–1.001) P = .0515 | 0.684 (0.444–1.051) P = .083 |
| Past year strenuous activity (U = 7 h/wk d ) | 1.235 (0.990–1.541) P = .0618 | 1.227 (0.981–1.534) P = .0727 | 1.364 (0.940–1.980) P = .101 |
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