Background: The outcomes of urine alkalization with alkaline water supplementation vary greatly across studies and therefore remain inconclusive, probably arising from differences in study design, ethnic group, and source of alkaline water, which needs further clarification. With a systematic review of literature, followed by an empirical observation among healthy Chinese volunteers, we aimed to investigate the outcomes of urine alkalization with alkaline water vs. daily drinking water, and whether these outcomes are intersected by certain factors such as gender and body mass index (BMI).
Methods: We conducted a literature search of related studies on alkaline water supplementation and urine pH using the PubMed, Embase, Medline and Cochrane Library databases. The publication bias was assessed with inverted funnel plotting. Chi-square-based Q-test and I2-statistic test were used to examine the data heterogeneity. The studies were evaluated for quality using the Cochrane risk of bias tool or Newcastle-Ottawa Scale (NOS). The meta-analysis was followed by a study in healthy volunteers. As per protocol, all subjects remained on regular drinking water for one week and were switched to alkaline water for the next week. Urine pH was measured thrice daily and averaged. The mean urine pH values in the first and second weeks were compared for all subjects. Alkalization gains in urine pH (AGU-pH) was computed to determine the outcome of alkaline water supplementation in relation to baseline urine pH.
Results: Our systematic review of literature yielded limited data about the effect of alkaline water on urine pH. Despite an increase in urine pH after supplementation of alkaline water as indicated by the random-effect model, a high heterogeneity across the included studies (I2=94%, P<0.001) precluded a robust determination. In our volunteer study, alkaline water led to elevation of urine pH from baseline in 84.9% of all subjects or by BMI stratification. Effective urine alkalization was noted in males but not in females. Subjects who presented effective urine alkalization had significantly lower baseline urine pH compared with those who did not (5.94±0.27 vs. 6.22±0.22, P=0.0016). The negative correlation between AGU-pH and baseline urine pH (r=-0.236, P=0.044) and receiver operating curve (ROC) analysis suggested that subjects with more "acidic" urine, particularly those with a baseline urine pH ≤6.0 (maximum Youden index =1.548, cut-off =5.977), could show more pronounced outcome of urine alkalization from oral alkaline water.
Conclusions: Our meta-analysis and human subjects study revealed that alkaline water supplementation may be useful for urine alkalization, particularly in individuals with a lower urine pH. The outcomes seem not significantly pronounced in females, although more efforts warranted for validation. Short-term use of alkaline water is well-tolerated and not associated with over-alkalization of the urine.
Keywords: Alkaline water; safety profile; urine alkalization; urine pH.
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