The explanation usually arrives before anyone has asked a question. A man in his seventies mentions that he is up three times a night, and someone at the table says “that’ll be the prostate”. A woman the same age gets told her bladder is not what it was. Both explanations are occasionally right, and both are reached without anybody measuring the one thing that would settle it.
Because the problem is often not the bladder at all. It is the kidneys, making urine at the wrong time of day. And the test that distinguishes the two costs a measuring jug and a biro.
TL;DR
- Nocturia means waking at least once a night to pass urine. It is the most common cause of disturbed sleep in older people, and roughly half of people in their eighties have it.
- In most older adults the cause is nocturnal polyuria: more than a third of the day’s urine is produced at night. A 2026 multicentre voiding-diary study of 875 adults found 67.4% met that criterion, and in men, having an enlarged prostate did not independently predict it.
- The only way to tell production from storage is a bladder diary with measured volumes. Ireland’s 76-page national urology model of care uses the word “diary” zero times and “nocturia” once, in a prostate questionnaire that counts trips and never asks about volume.
- Night-time urine production can be the first visible sign of untreated heart failure, sleep apnoea, kidney disease or poorly controlled diabetes, some of which a water-retaining medicine would make worse.
- Start the diary before you queue. There were 26,848 adults on Ireland’s urology outpatient waiting list in August 2026, and 9,824 of them had already been waiting more than six months.
What nocturia actually means
The International Continence Society defines nocturia as needing to wake at least once during the main sleep period to pass urine. That sounds almost trivially common, and it is: prevalence climbs steadily with age and passes 50% in people in their eighties. What is less often said is how much it costs. Nocturia is the single most common reason older adults have broken sleep, and in one survey around 70% of people who had it rated it as more than just a nuisance.
The arithmetic nobody does
There are only two ways to end up out of bed at 3am. Either your bladder cannot hold what is in it, or there is more in it than there should be. Those are completely different problems with completely different treatments, and telling them apart requires a number.
That number is the nocturnal polyuria index: the volume you pass overnight divided by your total volume across 24 hours. Above 0.33, which is to say more than a third of the day’s output arriving while you are meant to be asleep, and you have nocturnal polyuria. An alternative threshold is a night-time output above 90 ml per hour. Either way the diagnosis is a ratio, and a ratio needs measurements.
A study published in Neurourology and Urodynamics in September 2026 made exactly those measurements on 875 adults who had presented with nocturia as their main complaint at Japanese hospitals and clinics between 2018 and 2022, each keeping a voiding diary for at least two days. The findings are worth sitting with:
- 67.4% met the criterion for nocturnal polyuria. Two thirds of people who turned up complaining of night-time waking were producing too much urine at night, not storing too little.
- The index rose steadily with age. Median 0.28 in those under 50, 0.34 in their fifties and sixties, 0.39 in their seventies, 0.42 from 80 onwards.
- The prostate explained almost nothing. Of the 655 men in the study, 479 (73.1%) had benign prostatic hyperplasia. When the researchers built a statistical model of what predicted nocturnal polyuria in men, benign prostatic hyperplasia did not make the cut (odds ratio 0.67, 95% confidence interval 0.45 to 1.00). Age did. An overactive bladder did. Bladder capacity and total daily volume did. The prostate, present in three quarters of them, did not.
Worth saying plainly: this was a referred urology population in Japan, three quarters of them men, not a community sample of older adults in Ireland, so the exact percentages would not transfer. The structure of the finding, that the prostate is routinely blamed for a problem it does not predict, almost certainly does.
The counter-intuitive bit
The nocturnal polyuria index is a fraction, and it can rise because the top number goes up or because the bottom number goes down. In that cohort, the people aged 80 and over had the lowest total 24-hour urine volume and the lowest daytime volume of any age group. Their night-time volumes were higher than younger people’s, but the bigger shift was in the day: less fluid in, less urine out, and so the night-time share of a shrinking total grew. The authors make the point themselves, that an age-related rise in the index reflects falling daytime output as much as rising night-time production.
Which means the reflex instruction, cut down on fluids, can make the ratio worse while making dehydration, constipation and urinary infection more likely. Fluid timing is useful. Fluid restriction, applied blindly and all day, is not the same thing and is not harmless.
What the Irish system is set up to see
Ireland does have a national plan for urology. Urology: A Model of Care for Ireland was commissioned by the HSE through the National Clinical Programme in Surgery and published as Version 1 in the summer of 2019. It runs to 76 pages, and it is candid: “Continence care in Ireland is largely un-coordinated,” it says, and waiting times for prostate assessment are “exceptionally long”.
Search that document for the vocabulary of this problem and the result is stark. “Polyuria” appears zero times. “Desmopressin” zero times. “Fluid intake” zero times. “Diary” zero times. “Nocturia” appears exactly once, in 76 pages: as question seven of the International Prostate Symptom Score, reproduced in the model of care as the recommended screening tool for nurse-led male lower urinary tract clinics.
Look at what that question asks. “How many times did you typically get up at night to urinate?” Scored none, once, twice, three, four, five or more. It counts the trips. It asks nothing whatsoever about how much comes out, which is the only quantity that separates a production problem from a storage one. And it sits inside an instrument whose entire purpose is to score the prostate.
So the national pathway for a symptom that is largely a kidney and circadian problem runs through a prostate questionnaire, in a system the plan itself calls un-coordinated. That is not a failure of any individual GP or nurse. It is what happens when the tool to hand was built for a different question.
The causes that are not the bladder
Getting this right matters more than usual, because several of the things that drive night-time urine production are serious and some are made worse by the obvious treatment.
The heart. In congestive heart failure, atrial natriuretic peptide levels rise, and the kidneys shed fluid at night that the legs accumulated during the day. People with nocturia and high levels of that hormone may have heart failure that has not declared itself yet, and the guidance is to refer them to cardiology. A drug that makes you retain water would be precisely the wrong move.
Sleep apnoea. Obstructive sleep apnoea drives nocturia, and the worse the apnoea, the more trips. CPAP treatment can cut nocturia by one or more voids a night. If someone snores heavily, wakes unrefreshed and is up repeatedly, the bladder is the symptom and the breathing may be the cause. Our piece on obstructive sleep apnoea after 65 covers why the standard risk scores miss older adults entirely.
The kidneys and blood sugar. Chronic kidney disease impairs salt and water handling and produces nocturnal polyuria directly. Poorly controlled diabetes causes an osmotic diuresis. Both show up on a blood test.
Medicines and their timing. Diuretics taken late in the day will do at night what they are designed to do. Alcohol and caffeine both add to night-time output. Interestingly, a diuretic deliberately moved to mid-afternoon is a recognised strategy for nocturnal polyuria, because it clears the fluid before bedtime rather than after it.
Treatment, honestly
If the cause really is the prostate, treating the prostate helps, but less than people expect. In men followed for two years on alpha-blockers with or without 5-alpha-reductase inhibitors, 62% were still getting up more than twice a night, and the improvement in nocturia was only statistically significant in men under 80. Because the underlying problem is usually several problems at once, medical treatment aimed at the lower urinary tract in men with nocturia often performs no better than placebo overall. Our guide to prostate health after 50 sets out what those medicines do well.
Where nocturnal polyuria is confirmed on a diary, there is a licensed treatment in Ireland. Noqturina, a low-dose sublingual desmopressin, is authorised by the HPRA for nocturia due to idiopathic nocturnal polyuria. It is one of the very few medicines whose licensed dose differs by sex: 25 micrograms for women, 50 for men, an hour before bed. Women are roughly 2.7 times more sensitive to it, and at 50 micrograms women over 50 had a five-fold higher risk of low blood sodium than men.
The honest effect size, taken from the trials in the product’s own licensing documents: 25 micrograms reduced women’s nightly voids by 1.46 against 1.24 on placebo, and 50 micrograms gave men 1.25 against 0.88. The first stretch of undisturbed sleep lengthened by 49 minutes in women and 39 in men compared with placebo. Real, measurable, and modest. For someone whose night is broken into three pieces, an extra three quarters of an hour at the front of it may still be the difference between coping and not.
The safety conditions are strict and specific. In anyone 65 or over, serum sodium must be in the normal range before starting, checked again at four to eight days and again at one month, and the drug stopped if sodium falls below 135 mmol/L. Fluid is restricted from one hour before the dose until eight hours after. It is contraindicated in known or suspected heart failure, in moderate or severe kidney impairment, and in anyone with a history of low sodium, and the older nasal spray form cannot be started for nocturia at all over 65. We have written separately on low sodium after 70 and why a mildly low result is not the harmless number it looks like.
Why this is a falls question
STOPPFall, the European tool for identifying medicines that increase falls risk in later life, lists 14 drug classes. Three of them are things you might plausibly be given for a complaint of night-time waking: diuretics, alpha-blockers used for prostatic hyperplasia, and drugs for urinary frequency and incontinence. In TILDA’s Wave 6 data, roughly half of adults aged 70 and over who had a fall requiring medical attention were taking at least one falls-risk-increasing drug.
Add repeated trips across a dark landing, half asleep, on a tablet that drops your blood pressure when you stand. Our falls prevention guide covers the rest, but the cheapest intervention here is a plug-in night light on the route between bed and bathroom, fitted tonight.
Start the diary before you join the queue
On 27 August 2026 there were 26,848 adults on the outpatient waiting list for urology in Ireland, according to National Treatment Purchase Fund open data. Of those, 9,824 had been waiting more than six months and 710 more than 18 months. You cannot shorten that queue. You can arrive at it carrying the one piece of information nobody will otherwise have.
A bladder diary over three days, including at least two consecutive ones:
- Get a cheap plastic measuring jug, the kind sold for kitchen use, marked in millilitres.
- Measure and write down every void, with the time. Day and night, all of them.
- Note the time you went to bed and the time you got up. Night-time means bedtime to waking. The first void after you get up for the day counts as daytime.
- Record what you drank and when, including tea, alcohol and anything taken with tablets.
- Then do the sum. Add up the overnight volumes. Divide by the full 24-hour total. Above 0.33 and you are looking at nocturnal polyuria, and the conversation changes from your bladder to your kidneys, your heart, your breathing and your medicines.
Bring it to your GP with your full list of medicines and the times you take them, and ask three things: could this be production rather than storage, should my sodium, kidney function and blood sugar be checked, and could the timing of anything I take be moved. If first-line measures do not settle it, your GP or public health nurse can refer you for specialist continence assessment, where a frequency-volume chart is routine even though the national plan never mentions one.
At Críonna Health we keep returning to the same point: the most useful thing you can bring to a short appointment is a number nobody else has measured. Three nights with a jug is an unglamorous way to spend a week. It is also the difference between being handed a prostate questionnaire and being asked a better question.
This article is general information, not individual medical advice. Do not start, stop or re-time any prescribed medicine without speaking to your GP or pharmacist.
📷 Photo by Jp Valery on Unsplash
