Your Bladder and the Body Clock
Anyone who’s noticed they need to get up more often to go to the loo at night as the years go by won’t be surprised to know that around one-third of older adult night-time visits to Accident and Emergency Department leading to hospitalisation at night are linked to nature’s call – Association between toileting and falls in older adults admitted to the emergency department and hospitalised: a cross-sectional study.
The percentage is even higher at around 50% in hospitalised patients, with most reported in the early hours – between 4 and 6am – Machine Learning-Based Prediction of In-Hospital Falls in Adult Inpatients: A Retrospective Observational Multicenter Study (Preprint).
That’s painful and expensive –
The numbers vary depending on how you calculate them, this recent study in the US estimates that each fall incurs direct costs of around $35,365, with system-wide costs adding up to $62, 521 – Cost of Inpatient Falls and Cost-Benefit Analysis of Implementation of an Evidence-Based Fall Prevention Program. Here in the UK, when you stack up the cost of an ambulance call-out at £250 and an average hospital stay at £440 x 12 days, system-wide costs to the NHS add up to an eye-watering £6 million per day here in the UK alone. When you account for formal carer time to write up incident reports, lost income and out of pocket expenses for informal carers, let alone the pain, distress and reputational risk, it’s easy to see why there’s a thriving billion-dollar industry dedicated to night-time monitoring, falls detection and rapid response – Stop Falling: Start Saving Lives and Money.
So what if we can reduce the need to get up to take that risky trip in the first place – wouldn’t that be a win-win?
And what’s that got to do with light?
It turns out that your bladder is linked to your body clock in two important ways as this fascinating paper explains – Disruption of circadian rhythm as a potential pathogenesis of nocturia.
The first is through peripheral clocks in your kidneys that reduce the filtration rate and facilitate reabsorption of water, so you don’t produce as much urine in the first place.
The second is through the vasosuppressin system, also under circadian control that shifts the sensitivity threshold and relaxes the muscles to increase capacity, so you don’t feel the need to go.
This work builds on earlier research into the potential for melatonin to improve night-time bladder control, or nocturia – Role of circadian rhythms and melatonin in bladder function in heath and diseases.
But why not simply set the clock with light? (and darkness of course)
So I was excited to come across this recent paper by a Japanese team in led by the urologist Takeshi Okinami who has spent his career studying the bladder and increasingly interested in how the body clock drives that urge to pee – Circadian Lighting Was Associated with a Reduction in the Number of Hospitalized Patients Experiencing Falls: A Retrospective Observational Study.
They’d made the most of a deep renovation in part of the Akashi Ninjyu Hospital to upgrade the lights from the old fluorescent tubes to a circadian system. They didn’t do anything fancy – just went a bit above the WELL standard for daytime light exposure (275 v 250 Melanopic EDI for four hours in the morning), tuned the lights to warm in the evening and made sure it was dark at night.
They didn’t invest in any posh ‘sciency’ kit either, or get the nurses to run extra tests.
They just looked back at patient records to track changes in the number of falls and injuries sustained over the year before the move, and in the seven months afterwards. Same patient profile, same staff. Just an upgrade to the basic building services, a deep clean and a lick of paint – and new lights.
The sample size is relatively small (200 patients in the ‘before’ and 216 in the ‘after’), but the results are impressive.
A drop in falls from 39 to 26 per 1,000 patient/days (or 33% reduction), in line with similar studies and anecdotal evidence from my clients.
But just as impressive for me, the data showed a complete elimination of serious consequences of the falls, from three to 0: patients who fell in the pre-renovation facility suffered three painful injuries – ischial fracture, fractured ribs, and bruising with rib fracture. Those who fell after the renovation did not.
Takeshi is clear that, while other factors such as age and anticonvulsant medication are critical risk factors for falls, the substantial improvement they have seen is most likely thanks to an overall improvement in circadian health with reduced need for trips to the bathroom – Falls Health Needs Assessment.
When I asked whether he’s been able to extend the trial across the rest of the hospital, Takeshi explained that he struggled to justify the cost or the disruption of an unplanned retrofit in wards where patients are completely bed-bound – night-time toilet trips are not an issue there. But he’s actively looking for the next opportunity to make the case for the marginal extra spend as part of their rolling refurbishment programme because he’s seen first hand what a difference it makes.
And yet, beyond the occasional mention of ‘healthy homes’, reducing trip hazards, staff education and the potential for sensors and alarms to improve response times, I haven’t found a single guideline here in the UK that mentions light (and darkness of course), including this comprehensive review – Fall prevention in hospitals and nursing homes: Clinical practice guideline.
Perhaps we’re missing a trick?
I’ll be sharing the latest research and what that means for lighting specification at the LIA TechX in Birmingham on Thursday 4th of June. Lighting designer John Bullock will be talking through recent circadian projects in residential care too. Please join us there – Booking link is here.
It’s the International Day of Light!
Time to get geeky about this amazing stuff hiding in plain sight and ten factoids to impress your friends in the pub –
- Photons have zero rest mass but carry momentum, so light exerts measurable pressure. The Planetary Society’s LightSail 2 (2019) was a 5 kg satellite propelled solely by sunlight on a 32 m² mylar sail – LightSail 2 Spacecraft Successfully Demonstrates Flight by Light.
- Energy per photon scales inversely with wavelength. A violet 400 nm photon carries ~3.1 eV; a red 700 nm photon ~1.8 eV. Energy — not intensity — is why UV damages DNA and red light doesn’t. (E = hc/λ standard physics.)
- A photon takes 8 minutes 20 seconds to cross from the Sun’s surface to your eye — but the energy that produced it spent an estimated 170,000 years random-walking through the Sun’s dense core to reach the surface.
- An LED is a semiconductor positive-negative junction. When current crosses it, electrons drop into “holes” and the energy difference — the bandgap of the material — is released as a single photon. The bandgap sets the wavelength: gallium nitride for blue, indium-gallium-nitride alloys for green, gallium arsenide for red.
- LEDs can switch on and off in nanoseconds — fast enough to transmit data. Flicker at low speeds can cause headaches and worse, but it can be used as a kind of high-definition 3D morse code- a technology known as ‘Li-Fi’, with emerging potential for sensor and tracking integration – and even communication underwater – Towards multi-modal and cross-modal integration in LiFi-based sensing, A fast secure and more reliable underwater communication system based on light fidelity technology.
- The brilliant blue of a peacock tail isn’t pigment — the feathers contain only brown melanin. The colours are generated from the interaction of light with nano-scale photonic lattices that reflect specific wavelengths through interference – Biophotonics of diversely coloured peacock tail feathers.
- Firefly bioluminescence is one of the most efficient light sources known: close to 100% of the chemical energy emerges as photons with almost no heat. Incandescent bulbs are ~10%. Modern LEDs reach 40–50%. (Schramm, ChemBioChem 2024; National Wildlife Federation reference.)
- The womb is not dark. By the third trimester enough light penetrates the abdominal wall that fetuses respond to it. From around 26 weeks, fetuses turn their heads preferentially toward face-like patterns of light projected through the abdomen. (Reid et al., Current Biology 2017, 27:1825; Ronga et al., Developmental Science 2025.)
- The human body emits ultraweak light. Visible-range biophoton emission from skin runs at roughly 10–1,000 photons per cm² per second — about 1,000× too dim to see, and it follows a circadian rhythm that peaks in the late afternoon. (Kobayashi, Kikuchi & Okamura, PLOS ONE 2009, 4:e6256.)
- The entire visible spectrum spans less than one octave of wavelengths (~380–750 nm). For comparison, the human ear hears about 10 octaves.
I’m hoping to sneak some of these questions onto the Ropemaker’s weekly quiz so I can score some points for my team at last!