Presented at the NIH State-of-the-Science Conference: Prevention of Fecal and Urinary Incontinence in Adults - Bethesda, MD - December 10-12, 2007

Obesity, type 2 diabetes and urinary incontinence (UI) are common and costly disorders. Over 50% of American women are overweight (body mass index (BMI) 25–29.9 kg/m²) or obese (BMI >30 kg/m²), and type 2 diabetes is estimated to affect more than 12% of adults over age 40, including 19% of people over age 60.^1,2 UI affects nearly 50% of middle aged and older women.³ Obesity and diabetes each account for expenditures of more than $100 billion per year,⁴ and the direct cost of UI is more than $30 billion per year in the United States,⁵ which is greater than the annual direct costs for all gynecological and breast cancers combined.⁶

Obesity and UI. In epidemiological studies, obesity is one of the strongest modifiable independent risk factors for UI.^7–14 Incontinence is reported to be 50%–100% more prevalent among overweight women and two- to fourfold more prevalent among obese women compared to women of normal weight. Several studies have observed an independent association of BMI with stress and mixed types of UI, with these types being two- to fourfold more prevalent in obese women.^7,8,14 Although data are limited, urge UI may also be associated with increasing BMI.¹⁴ Waist circumference may be the specific aspect of obesity contributing to the prevalence and/or severity UI.^10,14

Incident UI is also associated with increasing weight. Two recent population-based, prospective cohort studies demonstrated over 5–10 years of follow-up that the odds of incident weekly UI increased by 7%–12% for all types of UI (stress, urge, and mixed) for each 1 kg/m² increase in BMI.^14,15 Incident UI also increased with increasing adult weight gain.¹⁵

Weight reduction is an effective treatment for UI.^16–19 In two trials of overweight and obese women with UI randomized to either a low-calorie liquid-diet program or a lifestyle and behavior change program (Program to Reduce Incontinence by Diet and Exercise (PRIDE)) vs. a control condition, women in the intervention groups had significantly decreased weekly frequency of UI episodes.^18,19 Even modest weight reduction of 3%–5% is a clinically feasible treatment option for incontinence that has comparable efficacy to other nonsurgical treatments for UI as well as the additional benefits of weight reduction.

Although the mechanism of the obesity–UI association is unknown, it is theorized that excess body weight increases abdominal pressure, which in turn increases bladder pressure and urethral mobility, leading to stress UI, and exacerbates detrusor instability.^16,18 Higher waist-to-hip ratio has also been shown to increase risk for UI independent of BMI.^10,14

Diabetes and UI. Recent evidence strongly suggests that that prediabetes (impaired fasting glucose) and diabetes are independent risk factors for UI.^{7,10,11,13,14,20–22} In population-based observational studies, there is similar prevalence of UI, both overall and by type, among prediabetic and diabetic women²² and UI is reported to be 50%–200% more prevalent in women with type 2 diabetes than among women with normal glucose levels.

Two observational studies showed that over 4–5 years of follow-up, women with type 2 diabetes were at a twofold increased risk of developing very severe UI.^14,21 Diabetes duration of 5 or more years, insulin treatment, and microvascular complications such as peripheral neuropathy and retinopathy may be important risk factors for developing UI.^11,21–23

Prevention or effective treatment of diabetes may also be an effective intervention for UI. Among women with prediabetes enrolled in the Diabetes Prevention Program (DPP), the prevalence of total weekly UI was significantly lower at the end of the trial among women randomized to the intensive lifestyle (weight loss and exercise) group than those randomized to metformin or placebo groups.²⁴ Ongoing investigation in the Action for Health in Diabetes (Look AHEAD) randomized controlled trial of a behavioral weight loss program will investigate UI outcomes among overweight and obese individuals with type 2 diabetes. Therapies for microvascular complications of diabetes may be beneficial in the prevention or treatment of incontinence,²² and long-term follow-up in the DPP Outcomes Study and Look AHEAD will provide data on the effect of glycemic control and weight reduction on prevalent and incident UI among both prediabetic and diabetic populations.

Mechanisms by which type 2 diabetes may contribute to the development or severity of UI are not well understood.²⁵ Hyperglycemia in diabetics may cause an increased volume of urine, polyuria, or detrusor instability. Microvascular injury associated with diabetes, similar to the disease process involved in development of retinopathy, nephropathy, and peripheral neuropathy, might damage the innervation of the bladder or alter detrusor muscle function.

Fecal Incontinence. Limited studies have evaluated risk factors for fecal incontinence (FI), but evidence suggests that both obesity and diabetes are independent risk factors for FI. In population-based observational studies, FI is reported to be approximately 50% more prevalent in obese compared to normal weight women.^26–29

FI is reported to be 40%–200% more prevalent in women with type 2 diabetes than in women with normal glucose levels.^27,29–32 One study observed a significant dose-response relationship between self-reported glycemic control and the prevalence of FI, with higher prevalence associated with poorer level of glycemic control.³²

Increasing frequency of FI has been observed to be independently and positively associated with both obesity and diabetes.²⁷ In addition, women with both diabetes and obesity have a 3.5-fold higher likelihood of reporting FI compared to those without these prevalent conditions.³³

FI is believed to result from an imbalance of the propulsive forces of stool with the resistive mechanisms of the pelvis. Conditions that cause increased abdominal pressure (obesity), increased intestinal motility or loose stool (diabetes), and sphincter or pelvic floor weakness from an anatomic defect or nerve damage (diabetes) may all contribute to FI.²⁷

Summary. Obesity and diabetes are strong and independent risk factors for UI and FI. Since obesity and diabetes are preventable and modifiable conditions, the prospect of improved incontinence may help motivate people to undertake difficult lifestyle changes to reduce their more serious risks of obesity, diabetes, and their sequelae. For UI, future clinical trials of treatments among women with obesity and/or diabetes are critical. For FI, epidemiological studies are needed. Incontinence, obesity, and diabetes are common and costly: any treatment approach that can address these health problems simultaneously would be important for public health.

Written by: Subak L, M.D.

References

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