Dehydration Impairs Cognitive Performance: A Meta-analysis

Abstract:

Dehydration (DEH) is believed to impair cognitive performance but which domains are affected and at what magnitude of body mass loss (BML) remains unclear.

PURPOSE:

To conduct systematic literature review and meta-analysis to determine the effect size (ES) of DEH on cognitive performance and influence of experimental design factors (e.g., DEH > 2% BML).

METHODS:

Thirty-three studies were identified, providing 280 ES estimates from 413 subjects with DEH ranging from 1-6% BML. Outcome variables (accuracy, reaction time), cognitive domains, and methods to induce DEH varied. ES were calculated using standardized mean differences and multivariate meta-analysis.

RESULTS:

Impairment of cognitive performance (all domains/outcomes) with DEH was small but significant (ES = -0.21; 95% CI: [-0.31, -0.11], p < 0.0001) with significant heterogeneity (Q(279) = 696.0, p < 0.0001; I = 37.6%). Tasks of executive function (ES = -0.24; [-0.37, -0.12]), attention (ES = -0.52; 95% CI: [-0.66, -0.37]), and motor coordination (ES = -0.40; [-0.63, -0.17]) were significantly impaired (p ≤ 0.01) following DEH; and, attention/motor coordination was different (p < 0.001) from reaction time specific tasks (ES = -0.10; [-0.23, 0.02]). BML was associated with the ES for cognitive impairment (p = 0.04); consequently, impairment was greater (p = 0.04) for studies reporting >2% BML (ES = -0.28, 95% CI: [-0.41, -0.16] compared to ≤ 2% (ES = -0.14, 95% CI: [-0.27, -0.00]).

CONCLUSIONS:

Despite variability among studies, DEH impairs cognitive performance, particularly for tasks involving attention, executive function, and motor coordination when water deficits exceed 2% body mass loss.