The body of an older person has undergone changes that make adaptation to environmental extremes challenging.
The skin gets much thinner as a result of loss of tissues in all of its layers, leading to a decrease in its ability to prevent water evaporation. This also makes the skin more easily susceptible to sunburns. Thermoregulation (the ability to maintain a stable internal body temperature), which controls blood flow through the skin, is also not as vigorous anymore. Sweat gland numbers also decrease, lessening the efficacy of sweating as a means to cool down the body in hot environments.
Thirst sensation may be impaired. Older hearts and blood vessels may respond more slowly to changes in the blood volume from excessive water loss. The ability of the kidneys to conserve both water and electrolytes may also be limited because of age-related decreases in the filtration and tubular units. Hormonal levels related to water and temperature regulation in the body may be erratic, making the responses to environmental stress less predictable. Finally, the ability of the brain to coordinate control of internal body temperature may be less reliable as one ages.
Diseases that become more prevalent in the older person may further interact with the abovementioned physiologic changes. Kidney and heart diseases may limit the actual amount of water that can be taken in by an older person for a particular day. Furthermore, heart disease may limit the compensatory responses to dehydration.
Dementia, which leads to memory impairment and eventual functional deterioration, may drastically impair an older person’s judgement and insight to consciously drink water or avoid heat exposure. Certain medications may predispose to further dehydration like diuretics (medications that increase urination). Even simple arthritis may impair the older person’s ability to move around the house to get a drink of water or go to a cooler place.