Hydration is a term that describes the fluid and electrolyte concentration in the human body. The level of hydration is dependent on water intake from foods, liquid, metabolism and water loss from sweating and organ function. Adequate hydration is important because water accounts for 70% of body weight in humans and is essential to all physiologic functions. Water facilitates excretion of metabolic wastes by the kidneys and serves as a catalyst for most enzymatic reactions in the body including digestion, absorption, transport and metabolism of nutrients. Water maintains joint and skin health, facilitates optimal organ and tissue function and helps one to maintain an overall healthy body balance.

Aging is associated with several physiological changes that have a significant negative impact on total body water levels. A decrease in fat-free mass, which contains about 75% water, is observed with aging and contributes to dehydration in the elderly. As a consequence, older adults have approximately 60% body water compared to 70% in younger adults. Furthermore, the thirst sensation, which is the main stimulus for water intake, is blunted in the elderly. Due to this blunted thirst response, older adults generally have a lower fluid intake than their younger counterparts [1]. The part of the brain known as the mid cingulate cortex is often hindered in the elderly population and is the main contributor of a blunted thirst response [2]. Since mild dehydration produces sensations of thirst, elderly persons may not recognize the normal physiological signs of dehydration. The kidneys allow more water volume to be excreted with increasing age [3]. The prevalence of diuretic use, which exacerbates fluid losses and increases dehydration risk, is greater in the elderly. Finally, the tendency of drier skin in elder adults is partially explained by the decrease in water content of the stratum corneum, the outermost layer of skin [4].

When water loss is greater than water intake, dehydration can occur. Although there is no absolute definition of dehydration, tracking body weight provides a reasonable indicator of hydration status. Mild dehydration, characterized by a loss of 2-5% in body weight, results in weight loss, thirst and mouth dryness. If dehydration progresses, dangerously high body temperature, reduced cardiac output and kidney failure can occur. Once 15% of body weight is lost, death is imminent and is most commonly caused by brain damage, cardiac arrhythmia or kidney failure.

Older individuals have a higher risk of becoming dehydrated than younger adults [5]. Dehydration is the most common fluid and electrolyte disorder in the elderly with a prevalence of 20-40% [6] and is a frequent cause of morbidity in the elderly. Complications can include reduced mental function, thromboembolic events, infectious disease and kidney stones. The incidence of mortality incidence is also higher in dehydrated vs. hydrated elderly patients.

Due to the negative physiologic effects associated with dehydration, the elderly are advised to consume at least 8 cups of fluid per day under normal conditions. Fluid intake can be in the form of food or liquid [7]. Fluid intake should be increased above 8 cups if any of the following conditions are present: diarrhea, vomiting, bleeding, edema, infection, fever, exposure to warm environments or diuretic use. Unfortunately, 25% of persons over 85 years of age drink under 1 liter of fluid per day. Conversely, overconsumption of water may cause water intoxication in older adults as a result of the decline in the kidneys ability to dilute urine.

To ensure adequate hydration in the elderly, several strategies can be implemented. A regular drinking schedule is effective in maintaining safe daily fluid intake, utilizing either a written schedule or verbal prompting. Elderly people should monitor body weight at least once per week to ensure weight is maintained within a narrow range. Urine color should be clear or slightly yellow. Dark yellow or orange urine is very concentrated and implies a dehydrated state. Geriatric caregivers also play a vital role in helping to prevent dehydration. Patient education regarding hydration strategies is also critical. When older adults are taught that thirst is an unreliable indicator of hydration, water intake increases. Fluid intake has been shown to increase when older persons are provided different beverage options which include phytonutrient rich fruit and vegetable juices which offer some of nature’s best liquid vitamins. Other methods that can be utilized to maintain hydration in the elderly are keeping liquids easily accessible, encouraging family members to participate in feeding and recording daily fluid intake. Furthermore, taking medication with fluids should be encouraged as this is associated with greater daily fluid intake. [8].

In summary, aging is associated with fluid intake reductions and greater risk of dehydration. Dehydration in the elderly is associated with a higher complication rate and must be regularly monitored. Regular follow-up from caregivers and patient education on strategies to maintain adequate hydration levels are essential to preserve optimal health in older age.

Dr Linda Posch, MS SLP ND

References

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2. Farrell, M.J., et al., Unique, common, and interacting cortical correlates of thirst and pain. Proc Natl Acad Sci U S A, 2006. 103(7): p. 2416-21.

3. Beck, L.H., The aging kidney. Defending a delicate balance of fluid and electrolytes. Geriatrics, 2000. 55(4): p. 26-8, 31-2.

4. Berardesca, E. and H.I. Maibach, Transepidermal water loss and skin surface hydration in the non invasive assessment of stratum corneum function. Derm Beruf Umwelt, 1990. 38(2): p. 50-3.

5. Ferry, M., Strategies for ensuring good hydration in the elderly. Nutr Rev, 2005. 63(6 Pt 2): p. S22-9.

6. Lavizzo-Mourey, R., J. Johnson, and P. Stolley, Risk factors for dehydration among elderly nursing home residents. J Am Geriatr Soc, 1988. 36(3): p. 213-8.

7. Valtin, H., "Drink at least eight glasses of water a day." Really? Is there scientific evidence for "8 x 8"? Am J Physiol Regul Integr Comp Physiol, 2002. 283(5): p. R993-1004.

8. Chidester, J.C. and A.A. Spangler, Fluid intake in the institutionalized elderly. J Am Diet Assoc, 1997. 97(1): p. 23-8; quiz 29-30.