Hippocrates stated that older adults showed a general decline in total body water, and even declared that this loss of body water was the cause of all symptoms of aging. Recent cross-sectional and longitudinal studies in healthy older adult populations have unequivocally confirmed this classical dogma of a decrease in body hydration with increasing age, but only in the sense of a decrease in the absolute amount of TBW. However, it is difficult to accurately predict body hydration of individual older adults because of the large interindividual differences in body hydration. Nevertheless, the mean decrease of TBW with aging is an important risk factor for the occurrence of dehydration, though it is largely unknown how the decline in TBW affects hydration of individual organs and tissues. The skin often seems to be much drier among older adults. This is only partly explained by the small decrease in water content of the stratum corneum of the skin. Other histopathological changes must contribute substantially to the dry appearance of old age skin.
The severity of dehydration depends more on the relative than on the absolute loss of total, intracellular, and extracellular water. The lower an individual's body weight and optimal amount of TBW, the sooner the loss of a relatively small amount of body water will cause symptoms and signs of dehydration. This is the reason why the reduction in total body water as an unavoidable part of aging is an intrinsic risk factor for the development of dehydration among older adults. Reduced thirst and renal water conservation capacity are also risk factors, probably associated with aging per se.[5,7,8,15] If older adults are functioning independently they fulfill their daily needs for water easily with bouts associated with their meals and social drinks.[6,16] However, with increasing age a substantial number of older adults (up to 25% of persons age 85 and over) drinks less than 1 litre of fluids per day. The limited capacity of homeostatic mechanisms to maintain fluid balance only becomes important when fluid balance is at risk.
Environmental and disease-related risk factors for dehydration have a very high prevalence among older adults. Lavizzo-Mourey identified the most important risk factors for dehydration in a large prospective study on a LTC population. Being over 85 years old and female, having five or more chronic diseases, taking five or more kinds of medication, and being bedridden were significant risk factors in developing a moderate degree of dehydration. In the case of severe dehydration the odds ratios for these risk factors were very high. The weather (particularly hot weather), inability to feed oneself, poor mobility, and a low level of care were also significant but less prominent risk factors. Having Alzheimer's disease is an additional risk factor after having controlled for all these factors, because it is associated with increased dependence on others for sufficient water intake and physiological changes such as a low arginine vasopressine (AVP) level. Individuals in an AVP-deficient state are prone to dehydration because of having a poor water concentrating capacity. Lavizzo-Mourey's risk factors are presented in Table 1 , together with the most important causes of hypernatremic dehydration.[13,19,20,21,22,23] These risk factors should be important triggers to alert physicians and nurses to the possibility of dehydration in older adult patients.
Geriatrics and Aging. 2007;10(9):590-596. © 2007 1453987 Ontario, Ltd.
Cite this: Dehydration in Geriatrics - Medscape - Oct 01, 2007.