Water-loss dehydration and aging☆
Introduction
As we age the proportion of fluid in our bodies reduces, from over 70% of our weight as newborn babies, to 60% in childhood and about 50% in older people (Altman, 1961, Friis-Hansen et al., 1951, Greenleaf, 1998, Olde Rikkert et al., 1997). As body water falls with age, the buffering capacity against dehydration is reduced, which can have serious consequences to health and wellbeing (Olde Rikkert et al., 2009). According to Aristotle, over 2000 years ago, “old age is dry and cold” (Aristotle, 350 B.C.).
Water is central to every activity of the human body. Life arose in the water, and every human being starts life in utero in a watery environment, but humans are land creatures who have to carry their watery environment around inside them. The aqueous intracellular environment is essential for biochemical processes, and water is central for the maintenance of the circulation, the lymphatic system, body temperature, removal of waste products from cells and from the body, facilitating ingestion and digestion, acting as a lubricant, and flushing out the urinary tract, eyes and other crucial organs. In the absence of fluid intake death occurs in a few days to a week, far more quickly than due to the absence of any other nutrient.
Section snippets
Definition of water-loss dehydration and salt-loss dehydration
There are several types of dehydration, with distinct causes and treatments. The Dehydration Council defines dehydration as “a complex condition resulting in a reduction in total body water” and suggests that the main types are water-loss dehydration and salt-loss dehydration (Thomas et al., 2008), while EFSA calls it “the process of losing body water and leads eventually to hypohydration (the condition of body water deficit)” (EFSA Panel on Dietetic Products, 2010). Water-loss (or hypertonic)
The reference (or gold) standard for dehydration
There are a variety of ways that physicians and scientists may determine whether an individual is truly dehydrated, and there has been debate about the best measure(s), the gold standard or reference standard, to use (Armstrong, 2007). Potential reference standards for dehydration include:
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Plasma urea/creatinine ratio, which appears useful when kidneys function well, but in older populations raised ratios may also be due to renal failure, bleeding, heart failure, sarcopenia, glucocorticoids or
Signs of dehydration in older people
Although serum osmolality defines the state of water-loss dehydration (is the gold standard), it would be helpful to be able to use simple indicative signs of early dehydration in older people to alert older people and their carers to impending dehydration. This is because regular blood tests are not feasible or practical in the community or residential care settings (Leibovitz et al., 2007), results may take some time to arrive and can be costly. Such signs would allow dehydration to be
Prevalence of dehydration in older people
Salt-loss dehydration is present in 0.5–2% of free-living population samples of US people aged at least 70 years (defined in these studies as serum tonicity <285 mmol/L or low serum tonicity plus orthostatic hypotension) (Stookey, 2005, Stookey et al., 2005). The proportions of elderly people in these cohorts with water-loss dehydration were much higher, with 21% of the 70+ year olds in the Duke component of the Established Populations for Epidemiologic Studies of the Elderly (EPESE) cohort (
Why older people are more at risk of water-loss dehydration
All land animals need to be able to regulate their hydration levels in order to survive. In humans, drinking less leads to a rise in sodium levels in the extracellular fluid. To equalise the osmolality between the intracellular (67% of total body water) and extracellular (33% of total body water) fluids there is a movement of water from within cells into the extracellular fluid, causing the osmolality of the intracellular fluid to rise and cells to shrink. Cellular osmoreceptors in the organum
Helping older people to prevent dehydration
In older people who are living in the community or in residential care and nursing homes issues surrounding drinking and eating (fluid supply) and urination (fluid removal) need to be addressed in order to promote optimal hydration. The areas that need to be considered are personal factors, habits and preferences; social and environmental conditions; and systems of care and support.
How much older people drink and how we measure it
The minimum fluid requirement for an individual has been defined as ‘the amount of water that equals losses and prevents adverse effects of insufficient water’ (EFSA Panel on Dietetic Products, 2010). Fluid is obtained from both food and drinks, but beverages (such as plain or flavoured water, tea, coffee, other hot drinks, milk and milk products, fruit juices, soft drinks and alcohol) account for 70–80% of fluid intake in most populations (Bellisle et al., 2010, Kant et al., 2009).
There is no
The effect of water-loss dehydration on the health of older people
We know that water-loss dehydration is associated with many chronic health problems in older people, including falls, fractures, confusion, delirium, pressure ulcers, poor wound healing, constipation, urinary tract infections, heat stress, infections, kidney stones, renal failure, drug toxicity, stroke and myocardial infarction (Chan et al., 2002, Olde Rikkert et al., 2009, Rolland et al., 2006, Thomas et al., 2008, Wakefield et al., 2008). Extreme dehydration is an emergency medical condition
Research needed in dehydration and older people
Further research is required in this area. We need to develop ways of screening for early stage dehydration in the elderly, and develop best practice for helping older people to consume sufficient liquids in care homes and in the community. Older people and their carers (both formal and informal) require training to recognise early signs of dehydration and we need strategies for promoting drinking. As part of this we must better understand fluid intake variability in older people, and daily
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This report is independent research arising from a Career Development Fellowship supported by the National Institute for Health Research and has received funding from the Seventh Framework Programme (FP7/2007–2013) under grant agreement n. 266486 (NU-AGE project entitled “New dietary strategies addressing the specific needs of elderly population for a healthy ageing in Europe”), ClinicalTrials.gov Identifier: NCT01754012. The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, the National Institute for Health Research or the Department of Health.