Anatomical changes to the urinary system with ageing
Along with the rest of the body, the urinary system can be affected by normal changes related to ageing. When considering continence issues with your patients, it is important to bear these changes in mind, especially if you have cared for a patient for a long time as these changes will be happening alongside changes in their clinical condition. Age-related changes may also affect how well some medicines work, particularly medicines used to manage overactive bladder and other lower urinary tract symptoms.
Structural changes to the kidneys, bladder and urethra
Muscle changes and changes in the reproductive system can affect bladder control. Changes in the kidneys with age include:
A decrease in the amount of kidney tissue and reduction in kidney function
The number of nephrons (parts of the kidney that filter waste material from the blood) decreases
Hardening of the blood vessels that supply the kidney, which causes the kidneys to filter the blood more slowly (Brodkey, 2024).
Changes in the bladder with age include:
Changes to the bladder wall – the elastic tissue becomes stiffer because more collagen fibres are deposited in the wall and the bladder becomes less stretchy, which means that the bladder cannot hold the same volume of urine as it was able to previously
Weakening of the bladder muscles
Partial or total blockage of the urethra. In women, this can be a result of a prolapse of the bladder or vagina, and in men it can be caused by an enlarged prostate gland (Brodkey, 2024).
Ageing increases the risk of kidney and bladder problems including bladder control issues such as leakage, urinary incontinence or urinary retention; urinary tract or bladder infections; and chronic kidney disease. The pelvic floor muscles often weaken, which also affects continence.
Functional and urodynamic effects
Alongside the anatomical changes outlined above, there are some additional issues which can affect the urinary system.
Increased volume of residual urine
Two of these anatomical changes (weakening of bladder muscle and blockage of the urethra) can cause an increase in the amount of urine left in the bladder after voiding (residual urine). This can contribute to asymptomatic bacteriuria, where bacteria are present in the urine without symptoms of infection. In most people this does not need antibiotic treatment, but it can lead to positive urine tests and unnecessary antibiotic prescribing if symptoms are not assessed carefully.
Nocturia
At night, levels of antidiuretic hormone (also called vasopressin) increase to signal to the kidneys to reabsorb more water, leading to reduced need to urinate overnight, hence more concentrated urine is produced. The size of this surge in antidiuretic hormone decreases with age, meaning that the kidneys produce a larger volume of urine which often leads to an increased need to wake up and urinate during the night.
Nocturia is often multifactorial, so fluid intake, medicines, sleep disturbance, diabetes, heart failure, oedema and urinary symptoms should also be considered.
Slower rate of urinary flow
Again, a number of the changes of ageing can cause the rate of urine flow to slow down. These include weakened bladder muscles, the stiffer bladder wall and reduced muscle contractility. In men this can be further hindered by the age-related enlargement of the prostate, and in women issues with pelvic floor muscles and changes to the urethra following menopause can also reduce the rate of flow of urine.
Higher risk of infection
The increased level of residual urine mentioned above, alongside changes to the tissues of the urinary system (such as a thinner urethral lining in women post-menopause) can lead to a higher risk of urinary tract infections. In older adults, assessment should focus on new urinary symptoms and signs of infection, rather than urine dipstick or culture results alone.
Changes to the nervous system
The link between the brain and the bladder also changes with age. The brain–bladder axis experiences changes from both the central nervous system (CNS) and the bladder, as outlined above. Age-related changes may include an increased reliance on an intact CNS, less precise CNS control over the bladder reflex, and reduced ability of sensory nerves (i.e. those signalling that the bladder is full) to accurately transmit this information to the brain (Hardy and Korstanje, 2023). These changes can also lead to increased involuntary contractions of the bladder, which often result in urge incontinence or an overactive bladder.
Final thoughts
Next time you are assessing a patient, take a moment to think about whether any of these issues may be affecting their continence alongside their clinical condition.
Hardy CC, Korstanje R (2023) Aging and urinary control: Alterations in the brain-bladder axis. Aging Cell22(12): e13990. https://doi.org/10.1111/acel.13990
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