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BACKGROUND: Bowel and urinary habits are known to be closely related in children with voiding dysfunction and men with lower urinary tract symptoms. However, to our knowledge, the association between bowel and urinary function in women has not been assessed in large population-based studies. The goal of this study is to determine whether bowel habits affect urinary incontinence and nocturia in middle aged and elderly women.
METHODS: National Health and Nutrition Examination Survey (NHANES) is an annual survey instrument administered by the Centers for Disease Control to a nationally representative sample of 5000 people. This study included 1295 women older than 40 years, who were surveyed in the 2009-2010 NHANES. Stress incontinence, urge incontinence, frequency of incontinence and frequency of nocturia were self-reported. Incontinence was considered frequent when it occurred more than once per month, and nocturia was considered severe when it occurred more than twice per night. Degree of self-reported constipation, diarrhea, and the quality of stools, based on the Bristol Stool Scale, were used as predictive variables. Association between urinary symptoms and bowel habits was assessed using a nominal logistic regression adjusting for age, race, body mass index, alcohol intake, smoking, presence of diabetes, and parity, which are known risk factors for urinary dysfunction in women.
RESULTS: Severity of diarrhea and constipation were found to be significant risk factors for urge incontinence, stress incontinence and degree of incontinence in a model adjusted for other predictors (Table 1). Severity of constipation, but not diarrhea, was also significantly associated with degree of nocturia (Table 1). Similarly, hard stools (Bristol scale 1 and 2), but not loose stools (Bristol scale 5, 6 and 7) were a significant risk factor for nocturia; and both were significant predictors of urge incontinence and the degree of incontinence (Table 2). Interestingly, neither parameter was a significant predictor of stress incontinence (Table 2).
CONCLUSIONS: Abnormal bowel habits appear to have a significant correlation with urinary incontinence and nocturia in middle aged and elderly women. Constipation, in particular, was found to be associated closely with urinary symptoms. Although causation is not demonstrated in this study, it appears that correction of bowel habits, which are generally considered an adjustable risk factor, may offer improvement in urinary incontinence, urgency and nocturia in women.

Odds ratios for urinary symptoms per unit increase in severity of constipation or diarrhea

	Odds ratio for constipation (95% CI)	Odds ratio for diarrhea (95% CI)
Frequency of urinary incontinence	1.27 (1.13-1.42)	1.33 (1.15-1.53)
Urge incontinence	1.31 (1.09-1.38)	1.23 (1.14-1.52)
Stress incontinence	1.18 (1.06-1.32)	1.36 (1.19-1.57)
Severity of nocturia	1.30 (1.13-1.50)	p>0.05

Odds ratios for urinary symptoms when hard or loose stools are compared to normal stools

	Odds ratio for hard stools (95% CI)	Odds ratio for loose stools (95% CI)
Frequency of urinary incontinence	1.68 (1.09-2.58)	1.43 (1.05-1.94)
Urge incontinence	1.63 (1.06-2.50)	1.32 (1.02-1.79)
Stress incontinence	p>0.05	p>0.05
Severity of nocturia	1.89 (1.32-2.69)	p>0.05