Causes and Risk Factors of Overactive Bladder

The cause of overactive bladder (OAB) remains unclear but is believed to stem from multiple factors, some of which you can control and others you can't.

OAB, referred to as non-neurogenic overactive bladder, is diagnosed when there are no known neurologic (nervous system) causes of the symptoms. By contrast, neurogenic bladder is a condition in which neurologic problems (like strokes or spinal cord injuries) can cause an overactive as well as underactive bladder.

When diagnosing OAB, healthcare providers will explore both possibilities to not only pinpoint the underlying cause but formulate an effective treatment plan.

Common Causes

Overactive bladder causes you to have little or no control over your bladder, often resulting in urinary incontinence. Women are more affected by OAB than men.

When functioning normally, the detrusor muscle will start to contract when the bladder is about half-full, giving you plenty of time to run to the bathroom. With OAB, the muscle will contract and spasm well before then, resulting in frequent urination (urinary frequency), excessive urination (urgency), and nighttime urination (nocturia).

It is also possible that sudden, involuntary contractions in other parts of the lower urinary tract (including the urethra and prostate gland in males) might instigate a chain reaction that causes the detrusor muscle to spontaneously and inappropriately contract.

These physiological effects may be the result of a prior or current health condition that causes bladder overactivity. Some of these conditions may also affect the urethral sphincter muscles that control the exit of urine from the body, leading to leakage and incontinence.

Common causes of OAB include:

• Recurrent urinary tract infections, which some studies have linked to bladder hyperactivity, especially in women
• Pelvic organ prolapse, the severity of which coincides with an increased risk of OAB
• Enlarged prostate, which can place direct pressure on the bladder when it tries to empty
• Hip surgery or hip problems, both of which can alter the position of (and place undue stress on) the organs of the lower urinary tract
• Low estrogen levels, particularly after menopause, which can alter the structure and function of the detrusor and urethral sphincter muscles
• Kidney stones or bladder stones, which can alter the urinary biome and cause irritation to the bladder and rest of the lower urinary tract
• Urinary catheter use, which can directly irritate the bladder and/or prostate gland, the irritation of which may persist even after the catheter is removed
• Multiple vaginal births, of which the risk of OAB increases with each delivery as the pelvic floor muscles progressively weaken
• Heavy metal poisoning, with substances like lead or mercury causing cellular changes in the bladder that can lead to overactivity

Lifestyle Risk Factors

Certain lifestyle factors can increase the severity and/or frequency of OAB symptoms. They do not necessarily "cause" OAB but can increase the risk of bladder irritation, place stress on the bladder, or promote excessive urination. All of these are triggers for OAB.

There are six modifiable risk factors associated with OAB:

• Obesity: Both general obesity and central obesity (involving the excess accumulation of fat around the waist) appear to increase the risk of OAB in women more than men, particularly with respect to urinary frequency and nocturia.
• Caffeine: Caffeine is a diuretic and may increase urinary frequency and urgency when consumed in excess (although studies are conflicted on how much is too much). Coffee, tea, chocolate, colas, guarana, and energy drinks are common sources of caffeine.
• Overhydration: Even more than caffeine, excessive fluid intake can increase the frequency and severity of OAB symptoms. Studies have shown that a 25% reduction of daily fluid intake can significantly reduce the risk of urinary frequency, urgency, and nocturia (so long as not less than one liter is consumed per day).
• Alcohol: Alcohol is also a diuretic but can also increase urine acidity, triggering bladder irritation. Studies suggest that there are greater odds of urinary urgency and frequency among current drinkers compared to nondrinkers or ex-drinkers. The risk is higher in men, particularly those who consume more than two drinks per day.
• Smoking: Studies have shown that the severity of OAB is 2.54 greater in current smokers with OAB than those who do not smoke. Smoking appears to increase the risk of OAB due to the hardening of the arteries (atherosclerosis), a condition that affects the bladder as well as the cardiovascular system.
• Medications: Diuretics like Bumex (bumetanide), Dyrenium (triamterene), Hydrodiuril (hydrochlorothiazide), and Lasix (furosemide) increase urinary output and make OAB symptoms worse. The long-term use of diuretics is also linked to an increased risk of OAB in adults 75 and over.

Neurologic Causes

Although neurogenic bladder and non-neurogenic OAB are distinct disorders, there is a considerable overlap of symptoms, and the lines frequently blur between the two conditions. In some cases, nervous system problems may contribute to, rather than are, the primary cause of OAB.

One such example is age. In adults 75 and older, changes in the brain—specifically the cerebral cortex—affect the neural pathways that regulate bladder control. Changes in the anterior cingulate cortex especially (located at the back of the brain) can lead to increased bladder sensitivity and urinary urgency.

Other conditions can affect the normal neurologic function of the bladder, either directly or indirectly. Some of these conditions are aging-related, while others are not.

Common neurologic causes of OAB symptoms include:

• Previous stroke, with some studies suggesting that 28% of people with stroke with experience OAB
• Pelvic surgery or prostate surgery, both of which can sever or damage nerves that regulate the detrusor muscle
• Lower spinal cord injury and herniated discs, both of which are associated with urinary incontinence and the loss of bladder control
• Diabetes, the metabolic disorder can trigger progressive nerve damage, leading to the loss of urethral sphincter control
• Parkinson's disease, a neurogenerative disorder that increases the risk of OAB by 1.54-fold compared to the general population
• Multiple sclerosis, a progressive autoimmune disorder affecting nerve membranes that leads to OAB symptoms in around 62% of those affected
• Spina bifida, a spinal birth defect long associated with abnormal urinary function, including detrusor overactivity
• Alzheimer's disease, a progressive neurological disorder that leads to OAB in 73% of those affected

Genetics

There is some evidence, albeit weak, that some people are genetically predisposed to OAB. Although there are no genes specifically linked to OAB, epidemiological studies have suggested that the condition may run in families.

A Word From Verywell

Overactive bladder is a frustrating condition that is often difficult to diagnose and treat. Even so, the American Urological Society suggests that around 60% of people treated for OAB will experience the complete resolution of symptoms within a year.

Even if first-line therapies and medications fail to provide relief, there are minimally invasive treatments like botox injections, sacral neuromodulation (SNM), and percutaneous tibial nerve stimulation (PTSN) that have been shown to reduce severe OAB symptoms by 80% to 90%.

In the end, OAB isn't something you should "learn to live with." By being patient and working with your healthcare provider, you will more likely than not find a solution to this perplexing and all-too-common urologic disorder.