Thermoregulation is the body’s process for maintaining a stable internal temperature, a necessity for optimal physiological function. With advancing age, the precision and effectiveness of this system diminish, compromising the ability to keep the core temperature within a narrow, safe range. This decline leaves older adults highly susceptible to both hypothermia in cold environments and hyperthermia during heat exposure, due to failures in central control and peripheral responses.
Changes in Central Temperature Regulation
The primary control center for body temperature, located in the hypothalamus of the brain, becomes less responsive with age. This area acts as the body’s thermostat, receiving input from temperature sensors and initiating counter-responses when the core temperature deviates. Aging causes a blunted sensitivity in this central mechanism, slowing its ability to recognize and react to thermal stress.
This reduced sensitivity shifts the body’s set point, which is often slightly lower in older individuals. A lower baseline means the body might not perceive a cold environment as a threat until the core temperature has dropped to a more dangerous level. Similarly, the threshold temperature required to initiate heat-dissipating responses, like sweating, is often elevated or delayed in older adults.
Reduced Mechanisms for Generating and Conserving Heat
The body’s protective responses to cold, which involve both heat creation and heat retention, become impaired in older age. One of the most important conservation methods, peripheral vasoconstriction, is less effective; the blood vessels near the skin surface do not narrow as efficiently to shunt warm blood toward the internal organs. This attenuated response allows heat to escape more readily from the body’s extremities and surface, compromising the body’s insulating shell.
Heat generation is also compromised due to changes in body composition. Age-related muscle loss, known as sarcopenia, directly reduces the body’s capacity for shivering thermogenesis. Shivering, an involuntary muscle contraction that increases metabolic heat production, is less forceful and less sustained in older adults due to the reduced muscle mass. Even at rest, the basal metabolic rate is lower in older individuals, meaning less heat is produced.
Impaired Ability to Dissipate Heat
The body’s capacity to shed excess heat also declines, increasing the risk of heat-related illness. A key mechanism for cooling is evaporative heat loss through sweat, but with age, the functional output of individual sweat glands decreases. While the number of sweat glands does not necessarily change, the volume of sweat produced per gland is reduced, and the onset of sweating is often delayed until the core temperature is already dangerously high.
The circulatory system’s ability to transfer heat from the core to the skin surface for dissipation is impaired. Vasodilation, the widening of blood vessels, is less effective in older adults, resulting in a reduced flow of blood to the skin. This impairment is often linked to age-related endothelial dysfunction and a lower cardiac output, which limit the body’s capacity to pump the necessary volume of blood to the periphery. A diminished sensation of thirst also leads to a greater risk of dehydration. Dehydration further reduces the plasma volume needed for effective sweating and circulation, accelerating the rise in core temperature.
How Comorbidities and Medications Exacerbate Instability
Existing chronic health conditions complicate the thermoregulatory failures of aging. Cardiovascular disease directly impairs the ability to manage temperature extremes because effective heat transfer relies on the circulatory system. Conditions that reduce cardiac output, such as heart failure, limit the blood flow necessary for both cutaneous vasodilation in heat and effective vasoconstriction in cold. Poor circulation associated with diabetes or peripheral vascular disease also hinders the rapid redistribution of blood required for thermal stability.
Commonly prescribed medications interfere with the body’s already weakened thermal defenses. Diuretics increase fluid loss, predisposing a person to dehydration which impairs sweating. Medications with anticholinergic properties, including some psychiatric drugs, directly inhibit the function of sweat glands, blocking the evaporative cooling process. Beta-blockers can slow the heart rate response, making it harder for the body to circulate blood quickly enough to dissipate heat during thermal stress.