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Indoor cold exposure and nocturia: a cross-sectional analysis of the HEIKO-KYO study
Saeki K, Obayashi K, Kurumatani N.
BJU International 2016; 117: 829-835
Commented by Prof. Donald L. Bliwise
This is an interesting epidemiologic study suggesting that colder ambient temperatures may predispose for nocturia. Previous literature has not investigated a role of room temperature in nocturnal voiding, although one study reported higher rates of nocturia in winter, relative to summer months. Basic science studies suggest that detrusor activity is heightened by cold. The current study used a somewhat novel method of recording bedroom temperature over 48 hour period (daytime and nighttime) to determine if environmental temperature would be associated with relatively greater or fewer nocturia episodes.
Several features of this study bear mention. First, of course, these are observational data, and they are not based on interventions adjusting room temperatures. Ultimately, interpreting descriptive data as useful for practice would require an appropriately powered randomized clinical trial to test the intervention. Secondly, this study can be framed differently, if one approaches the more fundamental question as to whether it is nocturia that is responsive to temperature or whether it is sleep per se that responds to temperature, nocturia being relegated to simply being an outcome of disrupted sleep. From this perspective, the effect of ambient temperature on sleep could be the ultimate cause of nocturia, rather than detrusor overactivity or excess nocturnal urine production.
Sleep in mammals is highly dependent on temperature. Indeed, one of the numerous putative functions of sleep is to preserve thermoregulatory function, and in animal models, when sleep deprivation is prolonged, an animal’s ability to thermoregulate becomes severely compromised. In humans, sleep is associated with a shunting of core heat to the periphery and a subsequent cooling of internal temperature. Dutch researchers (Professor Van Someren et al) have shown that the efficiency with which heat is lost depends on the complete ambient environment for the sleeper, i.e., not merely air temperature but also temperature of the sleeper’s skin, which depends on factors like bedding (type and number of blankets, sheets, etc). Other studies have suggested that quality and depth of sleep can be strongly influenced by such “local” (in bed) temperature, which then may affect the sleeper’s ability to shunt heat. Suffice it to say, room temperature may have less bearing upon an individual’s sleep (and nocturia) than do nightclothes and type or quantity of bedding. The study by Saeki et al is quite provocative in suggesting that daytime (but not nighttime) room temperature may be associated with nocturia, but we know nothing in this study about the bed conditions in which people slept. Future studies should certainly pursue this line of inquiry, including more detailed measurements of skin temperature and polysomnographic measurements of sleep, as manipulations of environmental heating and cooling could potentially open new, non-pharmacologic avenues of treatment for nocturia.
To investigate the association between indoor cold exposure and the prevalence of nocturia in an elderly population.
SUBJECTS AND METHODS:
The temperature in the living rooms and bedrooms of 1 065 home-dwelling elderly volunteers (aged ≥60 years) was measured for 48 h. Nocturia (≥2 voids per night) and nocturnal urine production were determined using a urination diary and nocturnal urine collection, respectively.
The mean ± sd age of participants was 71.9 ± 7.1 years, and the prevalence of nocturia was 30.8%. A 1 °C decrease in daytime indoor temperature was associated with a higher odds ratio (OR) for nocturia (1.075, 95% confidence interval [CI] 1.026–1.126; P = 0.002), independently of outdoor temperature and other potential confounders such as basic characteristics (age, gender, body mass index, alcohol intake, smoking), comorbidities (diabetes, renal dysfunction), medications (calcium channel blocker, diuretics, sleeping pills), socio-economic status (education, household income), night-time dipping of ambulatory blood pressure, daytime physical activity, objectively measured sleep efficiency, and urinary 6-sulphatoxymelatonin excretion. The association remained significant after adjustment for nocturnal urine production rate (OR 1.095 [95% CI 1.042–1.150]; P < 0.001).
Indoor cold exposure during the daytime was independently associated with nocturia among elderly participants. The explanation for this association may be cold-induced detrusor overactivity. The prevalence of nocturia could be reduced by modification of the indoor thermal environment.