Water intake, hydration status and cognitive functions in older adults - a pilot study

This study aimed to assess the relationship between the hydration status and cognitive functioning of older adults. The novelty of the study was the simultaneous use of several indicators of hydration status, including plasma and urine osmolality, specific gravity and urine color, as well as the assessment of total body water content from body composition measurements, together with comprehensive cognitive assessment.

A cross-sectional pilot study included 35 participants aged ≥ 60 years. Water intake was assessed using the 3-day food record method. Hydration status was assessed by plasma osmolality (Posm), urine osmolality (Uosm), specific gravity (USG) and color (UC), extracellular water (ECW) and percentage of total body water (%TBW). Cognitive functions were assessed using a set of standardized neuropsychological tests including: two verbal tests (Digit Span, DS and Vocabulary, VT) from the Wechsler Adult Intelligence Scale, California Verbal Learning Test (CVLT), Verbal Fluency Test (VFT), Grooved Pegboard Test (GPT) and Global Cognitive Function (GCF).

The %TBW was the most strongly related to cognitive processes of all the measures of hydration status. %TBW was significantly related to the performance on memory/learning based on CVLT (r = -0.55, p = 0.002), after a short delay (r = -0.59, p = 0.001) and long delay (r = -0.57, p = 0.001) and GCF (r = -0.43, p = 0.019). Marked correlations were also present between %TBW and psychomotor speed using the GPT (r = 0.41, p = 0.028). Moreover, significant relationships were obtained in cluster analyses. Cluster 2 (lower hydration status) was characterized by lower water intake and AI% (% of Adequate Intake), higher Uosm, USG, UC, ECW and %TBC than cluster 1. At the same time, it had significantly higher scores for language ability: VT (p = 0.041) and VFT (p = 0.041).

Significant relationships between some indicators of hydration status and selected cognitive domains were observed. This pilot study complements previous research on the relationship between hydration status and cognitive function in older adults, emphasizing that even small changes in hydration status assessment parameters can affect cognitive outcomes. In healthy, free-living older adults without dehydration assessed by plasma osmolality, other parameters of hydration status, such as water intake and urine parameters, influence language functions, suggesting the need to assess multiple markers simultaneously. The long-term effect of low water intake should be evaluated in a larger study group.