This large-scale cross-sectional study of 128,889 individuals reveals distinct age- and gender-specific trajectories of urine osmolality in an East Asian population, confirming a universal age-related decline in renal concentrating capacity and a significant sexual dimorphism across all age groups.
Key Findings
Results
Males exhibited significantly higher mean urine osmolality than females across all age groups.
Overall mean Uosm was 657 mOsm/kg H2O (95% CI: 655–659) for males and 598 mOsm/kg H2O (95% CI: 596–600) for females.
The sexual dimorphism was described as 'profound and persistent' with p < 0.001 across all age groups.
The absolute difference between males and females was greatest in young adulthood.
The gap narrowed significantly in later life, with the narrowest difference observed in the >70–80 year age group.
The study population included 65,625 males and 63,264 females aged 20 to 89 years.
Results
Urine osmolality peaked in the 20–30 year age group and declined progressively with advancing age in both genders.
The decline was described as 'gradual until age 70, after which it accelerated markedly.'
The pattern was observed consistently in both males and females.
Data were stratified by gender and 10-year age increments spanning ages 20 to 89.
The authors characterized the decline as 'progressive' and 'inexorable' with advancing age.
Results
The rate of age-related decline in urine osmolality accelerated markedly after age 70.
The decline was gradual from age 20 through approximately age 70.
After age 70, the decline accelerated markedly in both genders.
This acceleration was identified as a specific vulnerability, highlighting 'a heightened risk of dehydration in the elderly.'
The narrowing of the male-female gap was most pronounced in the >70–80 year age group.
Methods
This study provides the first large-scale demographic map of renal concentrating capacity in an East Asian population.
The study analyzed retrospective data from 128,889 individuals at a single center in Shaoxing, China, between 2019 and 2022.
First-morning urine osmolality was estimated using the electrical conductivity method on a Sysmex UF-5000 analyzer.
Participants underwent routine physical examinations and were aged 20 to 89 years.
The authors described these as 'population-specific reference data' for a non-Western population.
Statistical analyses included independent t-tests and one-way ANOVA to compare mean Uosm values across groups.
Discussion
The observed sexual dimorphism in urine osmolality was attributed to the influence of gender hormones on renal water and solute handling.
The authors attributed the higher male Uosm to 'the influence of gender hormones on renal water and solute handling.'
The attenuation of the male-female difference in later life is consistent with hormonal shifts associated with aging.
The study described the sex difference as 'a significant sexual dimorphism attributable to the influence of gender hormones.'
No direct hormonal measurements were performed; the attribution is based on physiological interpretation of the observed data.
Conclusions
Higher urine osmolality in males was identified as predisposing to urolithiasis risk, while low urine osmolality in the elderly was linked to dehydration vulnerability.
The authors described 'an endemic risk of suboptimal hydration predisposing to urolithiasis in men.'
Elderly individuals were identified as having 'a heightened risk of dehydration' due to declining renal concentrating capacity.
The findings were said to underscore 'the need for age- and gender-stratified approaches in clinical nephrology, geriatric medicine, and public health.'
These clinical implications were drawn from the observed trajectories rather than from prospective outcome data.
Discussion
The age-related decline in urine osmolality was attributed to renal senescence and hormonal shifts.
The authors stated the findings 'confirm a universal pattern of age-related decline in renal function, likely driven by renal senescence and hormonal shifts.'
The term 'renal senescence' was used to describe the structural and functional deterioration of the kidney with age.
No direct biomarkers of renal senescence were measured; the attribution is mechanistic interpretation.
The acceleration of decline after age 70 was considered consistent with progressive renal aging.
What This Means
This research suggests that the kidney's ability to concentrate urine — a key measure of how well the kidneys are working — follows predictable patterns based on a person's age and sex. In a study of nearly 129,000 adults in China ranging from ages 20 to 89, researchers found that urine concentration was highest in young adults in their 20s and 30s and steadily declined as people aged. This decline was gradual through middle age but became much steeper after age 70, suggesting that kidney function related to water regulation drops off more sharply in older adults.
The study also found a consistent difference between males and females: males had notably more concentrated urine on average (657 vs. 598 mOsm/kg H2O) across all age groups, though this gap narrowed considerably in older age. The researchers attributed this difference to the effects of sex hormones on how the kidneys handle water and dissolved substances. Because males tend to concentrate their urine more, they may be at greater risk of kidney stones if they don't drink enough fluids, while older adults of both sexes face greater vulnerability to dehydration as their kidneys lose concentrating ability.
This research suggests that normal ranges for urine concentration should account for a person's age and sex, rather than using a single standard for everyone. The findings may be particularly useful for doctors managing kidney health, hydration, and related conditions in older patients or in clinical settings serving East Asian populations, where such large-scale reference data had not previously been available.
Zhou M, Wang Q, Zhang L. (2026). Age and Gender-Related Trajectories of Urine Osmolality in a Large-Scale Population Study: Physiological Mechanisms and Clinical Implications.. Clinical laboratory. https://doi.org/10.7754/Clin.Lab.2025.250802