Nocturia is a part of life for most older persons,  especially men,  nearly 90%  of whom experience at least one episode of nighttime voiding. It is often cited as one of the most bothersome of lower urinary tract symptoms (LUTS). Unlike the other common LUTS, nocturia can cause significant morbidity and even mortality for elderly persons.

At the same time, our understanding of nocturia in older persons is complicated by how this condition has been defined. The ICS definition of nocturia, the number of voids recorded during a night’s sleep with each void preceded and followed by sleep, assumes that “a night’s sleep” is relatively stable and consistently understood by patients. However, older persons spend more time in bed before falling asleep, and may count time in bed rather than time asleep when self-reporting nocturia. Older persons also experience more awakenings from sleep independent of comorbidity. When these awakenings are combined with age-associated shifts in diurnal urine output to later in the day and night, nocturia becomes essentially normal.  In older persons,  the number of nocturia episodes also should be placed in context of actual hours asleep and/or in bed, which can vary greatly.

For example, three episodes of nocturia over 6 h likely have a different pathophysiology and impact than three episodes over 12 h. 

Causes
In general nocturia affects older people more than younger adults, and those aged 65 or greater are more likely to experience a need to urinate at night. Many people with nocturia, especially elderly men, also experience concomitant lower urinary tract problems, such as frequency, urgency, weak stream, and incontinence -symptoms often attributed to benign prostatic obstruction. Age, childbirth, and menopause are often suggested contributors to nocturia in women. Multiple factors may cause nocturia in both men and women; these include behavioural patterns, diuretic medications, caffeine, alcohol, or excessive fluids before bedtime, and pathological conditions, such as prostatic disease, diabetes mellitus or diabetes insipidus, obstruction of the lower urinary tract, anxiety, or sleep disorders. The condition may also result from stroke, cardiovascular disease, peripheral oedema, and myeloneuropathy.

Nocturnal polyuria
Nocturnal polyuria was first defined by Asplund in 1995 as increased nocturnal output of urine, yet parameters to quantify urinary overproduction have been established only recently, with some researchers characterising the condition as night time urine volume in excess of 6.4 ml/kg. Others define it as nocturnal output exceeding one third of one’s total daily urine output; and still others consider nocturnal urine overproduction as a function of bladder capacity, determined via a recently developed nocturia index, which is defined as nocturnal urine volume divided by functional bladder capacity.

Functional bladder capacity is defined as the single largest volume voided and recorded in one’s voiding diary. If the nocturia index is greater than 1, nocturnal polyuria (excessive urination at night time) results, as nocturnal urine output exceeds the bladder’s maximal storage capacity. The condition may arise in some patients from a reverse in nocturnal or diurnal urine production, resulting from a disruption of the body’s diurnal secretion of arginine vasopressin, a hormone that increases resorption of water from the renal tubule, reducing volumes of concentrated urine. A possible explanation for this disruption is that persistent, long term urinary tract obstruction may create pressure induced lesions in the renal system, interfering with normal circadian renal handling of sodium by decreasing diurnal sodium excretion. Patients with respiratory diseases such as sleep apnoea may also experience nocturnal polyuria due to increased renal sodium and water excretion brought about by raised concentrations of atrial natriuretic peptide. Studies have shown that apnoeic respiratory obstruction creates hypoxia induced pulmonary vasoconstriction, increasing right atrial transmural pressure and raising peptide concentrations. Polysomnographic studies are recommended for patients with nocturnal polyuria who are also suspected of having obstructive sleep apnoea, especially those with obesity, asthma, hypertension, and adult onset diabetes mellitus. Nocturnal polyuria may also result from third spacing of fluid in the lower extremities caused by right congestive heart failure and venous stasis in the lower extremities. Detailed diagnostic tests such as an echocardiogram and nuclear testing should be completed in conjunction with a comprehensive history and physical examination for patients at risk of cardiac disease.