Because it has numerous functions in the human body, water is one of the most important nutrients and is essential in every life stage. However, with aging, the body’s mechanisms of water balance are disturbed, increasing the risk of dehydration among the elderly. Dehydration is indeed the most common fluid disorder among older persons, and it can have considerable clinical impact (Hodgkinson et al. 2003; Faes 2007). 
Existing evidence suggests high rates of dehydration in the elderly population (Begumand Johnson 2010; Himmelstein et al. 1983; Warren et al. 1994; Snyder et al. 1987; Bennett et al. 2004; Mentes et al. 2006a; O’Neill et al. 1990; Bourdel-Marchasson et al. 2004; Forsyth et al. 2008; Stookey et al. 2005a; Stookey 2005b), and dehydration is one of the ten most frequent diagnoses reported for hospitalisations of persons over 65 in the United States (Sheehy et al. 1999). More and more studies demonstrate the importance of preventing and managing dehydration to reduce its side-effects in this population (Faes 2007).

This document summarises the current scientific evidence on hydration in the aging population with a specific focus on the causes, consequences and management of dehydration.

I. The elderly: a population at risk of dehydration

Although there is no absolute definition, dehydration is typically defined as depletion in total body water content due to fluid losses, diminished fluid intake, or a combination of both (Begum and Johnson 2010).

Depending on the ratio between sodium and water losses, dehydration can be classified as isotonic (equal loss in sodium and water – example: diarrhoea), hypertonic (excess loss of water compared to sodium – example: fever) or hypotonic (excess loss of sodium compared to water – example: overuse of diuretics) (EFSA 2010).

In the elderly, several parameters can increase the risk of dehydration, the most important ones being the age-related physiological changes.

An older couple sitting on a park bench
Figure 1 - Age-related decrease in water body content
6L loss (15%)

41 L

70 kg
30 years old

35 L

70 kg
70 years old

Data from Hébuterne et al. 2009

I.1.2. Thirst sensation

The elderly often experience reduced thirst sensation which leads to decreased fluid consumption, especially following water deprivation (Schols et al. 2009; Kenney and Chiu 2001). Several hypotheses have been proposed, such as alteration in osmo- and baroreceptor function and changes in hormones and neurotransmitters (depletion of dopamine levels – a neurotransmitter involved in thirst induction –, increased level of plasma Atrial Natriuretic Peptide – ANP, a well-recognised thirst inhibitor – etc.) (Silver 1990; Wilson 1999). Due to this impaired regulation of thirst, older individuals often do not drink enough to properly rehydrate themselves after fluid deprivation (Sheehy et al. 1999; Kenney and Chiu 2001).

I.1.3.Kidney function

Also as a consequence of aging, renal water conservation is impaired. Aged kidneys are less able to concentrate urine, and thereby to retain water during water deprivation (Bennett 2000). Age-related lower responsiveness of the kidney to the Anti-Diuretic Hormone (ADH), is thought to play an important role in this loss of renal function (Sheehy et al. 1999).

In addition, aging kidneys have a lower ability to adequately regulate sodium excretion (Silver 1990).

Thus, in older individuals, aged-related physiological changes occur and these make the body less able to maintain water homeostasis (Schols et al. 2009) (Figure 2).

I.2. Additional factors

In addition to age-related physiological changes in the body, numerous other factors can put the elderly at increased risk of dehydration (Figure 3). The more risk factors, the greater the likelihood for dehydration (Wotton et al. 2008).
Aging is associated with limitations such as reduced swallowing capacity, reduced mobility, or comprehension and communication disorders, which can lead to insufficient fluid intake. Disease-related factors, such as fever, diabetes, or incontinence can increase water losses (Mentes 2006b; Weinberg et al. 1994; Feinsod et al. 2002). Dehydration may also be caused by environmental factors (warm temperature, inadequate knowledge or the lack of time of care workers in institutions contributing to inadequate fluid intake…) or iatrogenic factors (medications including laxatives, diuretics or angiotensinconverting enzyme inhibitors, and medical procedures such as those requiring fasting) (Faes 2007; Mentes 2006b; Amella 2004; Dyck 2007).

Risk factors of dehydration in the elderly

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