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Context The impact of food and drinks on body fluid metabolism is of direct clinical relevance but current evidence remains fragmented. Aim Synthesise current evidence on the role of food and drinks in urine production. Methods Systematic review as per PRISMA guidelines using MEDLINE and EMBASE databases (completed October 2019). Studies reporting on the effect of food, food constituents, and drinks on urine production were included. Two authors performed an independent extraction of relevant articles using predetermined data sets and completed quality‐of‐study indicators. Results A total of 49 studies were included, of which 21 enroled human subjects, and 28 were clinically relevant animal studies (all of which utilised rodent models). The included studies were determined to be of variable quality. High dietary sodium, as well as wine, spirits, high‐caffeine coffee, and caffeinated energy drinks, increased urine production in human studies. Decreased urine production was associated with low dietary sodium and consumption of milk, orange juice, and high‐salt/high‐sugar drinks. In animal models, a variety of fruits, vegetables, herbs, spices, and honey were associated with increased urine production. Conclusion Current evidence suggests that although several types of food and drinks may impact body fluid metabolism, the quality of the data is variable. Urine production appears to be influenced by multiple factors including composition (ie, moisture, macronutrients, and electrolytes), metabolite load, and the presence of specific diuresis‐promoting substances (eg, caffeine, alcohol) and other bioactive phytochemicals. Future research is needed to support current evidence and the physiologic mechanisms underlying these findings.

Urea is the most abundant and the largest contributing factor for urine osmolality. Urinary urea excretion is highly interrelated with dietary protein intake. Accordingly, an increase of urinary urea excretion due to high protein diet may lead to urea-induced osmotic diuresis. This study aims to explore the association between nocturnal polyuria (NP) and urea. This is a post hoc analysis of a prospective observational study of subjects who completed a renal function profile between October 2011 and February 2015 (n = 170). Each subject underwent a 24 h urine collection, which included 8 urine samples collected at 3 h intervals. Urine volume, osmolality, creatinine, urea and sodium were determined. Urinary urea excretion was used to estimate dietary protein intake. Compared to the control group, subjects with NP exhibited significantly higher nighttime urea and sodium excretion. Estimated evening dietary protein intake was correspondingly significantly higher amongst the NP subgroup. Nighttime diuresis rate was positively associated with age and nighttime free water clearance, creatinine clearance, sodium excretion, and urea excretion in NP subjects. Therefore, increased nocturnal urinary urea excretion may reflect an additional important mediator of nocturia owing to excess nocturnal urine production.

Background: The objective of this study is to evaluate current literature on the association between cognitive dysfunction and nocturia. Methods: A systematic review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was conducted through MEDLINE, EMBASE and COCHRANE databases and completed in November 2019. Randomized and non-randomized studies were included if they assessed the association between cognitive dysfunction and nocturia in older participants with or without neurological diseases. The quality of included studies was evaluated using the Risk of Bias Assessment tool for Non-randomized Studies (RoBANS). Results: A total of 8 cross-sectional studies conducted in older patient populations met the criteria for inclusion. A statistically significant association was identified in 6 studies on univariate analysis, which persisted in 2 studies after controlling for confounding factors. The association between cognitive dysfunction and nocturia was positive for all 6 significant analyses. The overall risk of bias was unclear. Conclusion: A significant positive association between cognitive dysfunction and nocturia was identified. However, research has been limited to cross-sectional studies, which precludes identification of causality between cognitive dysfunction and nocturia. Heightened awareness of the complex interplay between cognition and nocturia would allow professionals involved in the care of cognitively impaired patients with concomitant nocturia to more effectively manage these symptoms.