Influence of gender and body composition on hydration and body water spaces

SummaryBackground & aimsHydration disorders are frequent in clinical practice and can be a life threatening issue in frail patients. Mild dehydration (1–2% loss of body weight) appears to impair cognitive and muscular performance. There is, however, no infallible indicator of correct hydration, and of hydration disorders. This study aim at describing total body water (TBW), extra-cellular water (ECW) and intracellular water (ICW) in a cohort of healthy subjects varying in age, gender and body composition. Two indicators of cellular hydration (TBW over fat free mass, and ICW over fat free mass) were studied.MethodsThe study cohort was made of 944 men and 874 women (mean age 42.7 ± 13.1 yrs, BMI 24.3 ± 3.5 kg/m2). All were volunteers for a preventive health examination. TBW, ECW, ICW were measured with bioelectrical impedance analysis. Body composition was assessed with the 3-compartment model.ResultsValues for TBW, ECW, and ICW differed with gender and with BMI categories (lean, overweight, and obese). The ratio of TBW over weight decreased with increasing BMI and was lower in women than in men. ECW (as a proportion of TBW) increased with BMI. The ratio of TBW over fat free mass decreased in obese subjects. The ratio of ICW over fat free mass was normally distributed, and decreased with BMI, more so in women than in men.ConclusionsThis study provides reference values for body water spaces in healthy adults that are negatively correlated with BMI. Women and obese people display indicators of cellular dehydration, and are more at risk of dehydration.