Intracellular Water Content in Lean Mass is Associated with Muscle Strength, Functional Capacity, and Frailty in Community-Dwelling Elderly Individuals. A Cross-Sectional Study.

Mateu Serra-Prat,Isabel Lorenzo,Juan Yébenes,Mateu Cabré,Elisabet Palomera,Lluís Campins

doi:10.3390/nu11030661

Abstract

High intracellular water (ICW) content has been associated with better functional performance and a lower frailty risk in elderly people. However, it is not clear if the protective effect of high ICW is due to greater muscle mass or better muscle quality and cell hydration. We aimed to assess the relationship between ICW content in lean mass (LM) and muscle strength, functional performance, frailty, and other clinical characteristics in elderly people. In an observational cross-sectional study of community-dwelling subjects aged ≥75 years, ICW and LM were estimated by bioelectrical impedance, and the ICW/LM ratio (mL/kg) calculated. Muscle strength was measured as hand grip, frailty status was assessed according to Fried criteria, and functional status was assessed by Barthel score. For 324 recruited subjects (mean age 80 years), mean (SD) ICW/LM ratio was 408 (29.3) mL/kg. The ICW/LM ratio was negatively correlated with age (rs = −0.249; p < 0.001). A higher ICW/LM ratio was associated with greater muscle strength, better functional capacity, and a lower frailty risk, even when adjusted by age, sex, nº of co-morbidities, and LM. ICW content in LM (including the muscle) may influence muscle strength, functional capacity and frailty. However, further studies are needed to confirm this hypothesis.

Highlights

Water is an essential nutrient with structural, metabolic, transport and temperature control functions in the body
Our main results indicate that the intracellular water (ICW)/lean mass (LM) ratio decreases with age in elderly people, is higher in older men than in older women, and that a higher ICW/LM ratio is independently associated with greater muscle strength, better functional capacity and a lower frailty risk
The ICW/LM ratio varied relatively little, oscillating as it did between fairly narrow values, and it was associated in a plausible and coherent way with some clinical characteristics such as age, sex or the number of co-morbidities

Summary

Introduction

Water is an essential nutrient with structural, metabolic, transport and temperature control functions in the body. Total body water (TBW), which represents approximately 55–60% of the body weight of adults, is distributed in intracellular water (ICW) and extracellular water (ECW). Water exchange between intraand extracellular compartments is regulated mainly by osmotic pressure, with water flowing across the cell membrane to balance osmolarity on each side [1]. This transport is mediated by a family of membrane protein channels, called aquaporins (AQPs), expressed in response to specific stimuli [2]. Active transport of osmotically active compounds across the cell membrane indirectly contributes to water diffusion that balances ICW and ECW osmolarities.

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