A known risk factor for urinary incontinence in adults, especially women, is a BMI in the overweight range or above. However, the relationship of BMI to various types of urinary incontinence according to gender remains to be fully defined. In particular, data on its association in men are lacking, and relationship between BMI and urinary incontinence in older people have only been explored to a limited extent. Few longitudinal analyses are available to demonstrate the effect of rising BMI on incontinence incidence.  Therefore, our study aims to explore the association between BMI and urinary incontinence amongst Australian adults aged 70 years and above.

The ASPirin in Reducing Events in the Elderly (ASPREE) study was a randomised, double-blinded, placebo-controlled, longitudinal study of aspirin in 19,114 people aged 70 years and over in Australia and the US. Data regarding urinary incontinence were captured in the ASPREE Longitudinal Study of Older Persons (ALSOP) sub-study. For the present study, baseline data on Australian ALSOP participants were analysed using logistic regression to describe the presence and severity of stress and urge urinary incontinence for both men and women. At 3-years follow up, only stress urinary incontinence data remained available for logistic regression analysis. 

Participants with dementia, stroke, life expectancy <5 years, pre-existing severe incontinence causing dependence on care, and those unable to independently perform activities of daily living were excluded.

In Australia, 14,456 participants had stress urinary incontinence (SUI) data and 14,521 participants had urge incontinence (UUI) data available at baseline. At 3 years follow up, 11,814 participants had SUI data available. The participants had a mean age of 75.3 years at study entry, with a standard deviation (SD) of 4.3. The mean BMI was 27.9 (SD 4.5) and mean abdominal circumference was 96.9cm (SD 12.5). 

Elevated BMI at baseline was correlated with presence and severity for both types of urinary incontinence in both sexes. The overall unadjusted odds ratio per unit increase of BMI was 1.05 (1.04-1.06, p<0.01) for SUI and 1.04 (1.03-1.05, p<0.01) for UUI. The mean BMI results for those without incontinence versus those who reported incontinence on most days at baseline are presented in table 1.


The cumulative incidence for SUI at 3 years follow up was 17.25% (n=1045/6057). 

Those who developed new SUI during the 3 years follow up had a higher BMI (27.9, SD 4.2) than those who remained continent (27.5, SD 3.9), p=0.008. Furthermore, those whose SUI resolved were found to have a lower BMI than those whose SUI persisted over the same time period (27.8, SD 4.7 vs 28.4, SD 5.0). 

Our follow up data were analysed using logistic regression, adjusted for age, gender, smoking status, alcohol use, and diabetes. SUI was found to be associated with an increased BMI of 30 and above, with odds ratios (p=0.006) summarised in table 2 below.

Urinary incontinence was found to be significantly associated with BMI in community dwelling men and women over 70 years of age. Elevated BMI correlated with not only the presence, but also severity for both types of urinary incontinence in both sexes. Furthermore, in our study, the incidence of SUI and UUI increased more in those who have an elevated BMI, whilst a decreasing BMI was found to be associated with resolution of SUI.

Clinicians need to pay specific attention to the effects of BMI on older patients, when evaluating and treating them for any types of urinary incontinence.