Among the most well-established risk factors for SUI are elevated body mass index (BMI) and obesity.1,2 The strength of this association is emphasized by randomized clinical trial evidence demonstrating that weight loss of 8% of patients' body weight leads to meaningful reductions in the frequency of SUI episodes in obese women.4 These findings have reinforced that obesity is a modifiable driver of SUI.
However, despite the clarity of this relationship, BMI as a measure is inherently limited. It does not distinguish between fat and lean mass, nor does it capture the distribution of adipose tissue. As a result, reliance on BMI alone obscures potentially important biological differences among women with similar heights and body weights. Excess body weight is thought to increase intra-abdominal pressure, thereby increasing strain on the pelvic floor musculature and connective tissue that support the urethra. This mechanical stress may compromise urethral support, leading to leakage during activities that increase abdominal pressure. This may be due to concomitant expected rises in intra-abdominal pressure as well as consequences of metabolic dysfunction. Focused urodynamic analysis of obese women with incontinence has found that increased BMI and waist circumference both correlated with overall increasing intra-abdominal pressure, which translates to a greater prevalence of SUI.5 Another prospective trial of young women found that women with a similar parity, BMI, and total body weight had an increased risk of overall urinary incontinence when their total body fat and visceral fat weight increased6. However, the contribution of other aspects of inflammation, cardiovascular risk, physical activity, and dietary factors and their contribution to SUI remains an open question.
The present study was designed to address this gap by leveraging data from the National Health and Nutrition Examination Survey (NHANES), which provides a uniquely detailed and nationally representative large-scale dataset. We were able to analyze 6,276 women aged 20-60 years old, and by incorporating the gold standard in body composition analysis, dual energy X-ray absorptiometry (DXA) measurements, the study moves beyond crude anthropometric ratios to examine precise components of body composition, including total fat mass, visceral adiposity, and lean body mass. This approach allows for a more nuanced investigation into how different fat depots, particularly inflammatory visceral fat, may influence pelvic floor integrity and function. Additionally, the inclusion of reported physical activity, laboratory markers, and dietary intake data enables exploration of the interplay between metabolic health, nutrition, and SUI risk.
On univariate analysis, we found increased prevalence of SUI with increasing BMI, regardless of whether a patient is classified as obese or not. Interestingly, in the non-obese population, all increases in body mass, including total lean body mass, total fat mass, and truncal fat, were found to be associated with the presence of SUI. Conversely, increased subcutaneous fat percentage (and the ratio of subcutaneous to visceral fat ratio) was found to be inversely correlated. I.e. adipose tissue outside of the abdominal cavity was relatively protective against SUI compared to that found within the abdomen. Once patients were classified as obese, these nuances in body composition were lost as risk factors.
Multivariable analysis of both cohorts confirmed that the greatest risk factors are those commonly known to be associated with SUI, including increasing BMI, age, a history of smoking, and increasing vaginal parity as the greatest contributing factors. Nuances of body composition were no longer statistically significant in multivariable analysis. While BMI is not the end-all of vital parameters, it is an important descriptive variable that is correlated with stress incontinence risk. Also, by virtue of our findings, not all patients of similar BMI grouping are created the same.
There remains much to understand about the complex interplay of body composition, metabolic ill health, and stress incontinence. Our study is limited by its design, as a large-scale cross-sectional questionnaire study. Especially in the age of GLP-1 agonists and medication-induced weight loss, questions of changing body composition and its impact on SUI remain open and ripe for study.
Written by: Dylan T. Wolff,1 Joni K. Evans,2 Joseph Rigdon,2 Nicos Prokopiou,3 Maxwell Sandberg,3 Rahul Dutta,4 Amr El Haraki,3
- Department of Urology, Atrium Health Wake Forest Baptist, Winston-Salem, NC, USA.
- Department of Biostatistics, Atrium Health Wake Forest Baptist, Winston-Salem, NC, USA.
- Department of Urology, Atrium Health Wake Forest Baptist, Winston-Salem, NC, USA.
- Department of Urogynecology and Reconstructive Pelvic Surgery, University of Tennessee College of Medicine Chattanooga, Chattanooga, TN, USA.
- Minassian VA, Stewart WF, Wood GC. Urinary incontinence in women: variation in prevalence estimates and risk factors. Obstet Gynecol. 2008;111(2 Pt 1):324-31 doi:10.1097/01.AOG.0000267220.48987.17.
- Patel UJ, Godecker AL, Giles DL, Brown HW. Updated Prevalence of Urinary Incontinence in Women: 2015-2018 National Population-Based Survey Data. Female Pelvic Med Reconstr Surg. 2022;28(4):181-7 doi:10.1097/SPV.0000000000001127.
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- 5) Richter HE, Creasman JM, Myers DL, Wheeler TL, Burgio KL, Subak LL, et al. Urodynamic characterization of obese women with urinary incontinence undergoing a weight loss program: the Program to Reduce Incontinence by Diet and Exercise (PRIDE) trial. Int Urogynecol J Pelvic Floor Dysfunct. 2008;19(12):1653-8 doi:10.1007/s00192-008-0694-8.
- 6) Ferreira R, Sacramento J, Brasil C, Dias C, Placido C, Oliveira C, et al. Relationship of Body Composition and Urinary Incontinence in Women: A Cross-Sectional Case-Control Study. Female Pelvic Med Reconstr Surg. 2020;26(7):447-51 doi:10.1097/SPV.0000000000000834.