Why older adults are prone to hypothermia
Older adults are prone to hypothermia (a core body temperature below 35°C) because they retain heat less well and make less of it in the cold.
Remember
Older adults lose heat more readily and make less of it in the cold: the fat under their skin is thinner, their skin vasoconstriction is weaker, and their shivering (repeated muscle contraction that releases heat) is less effective. The effect varies from person to person.
Memory aid
an older person has a thinner coat (less fat), a weaker engine (less muscle to shiver) and sluggish valves (less skin vasoconstriction)
Picture the older person with a thinner coat, a weaker engine and sluggish valves to recall less insulation, less shivering and weaker skin vasoconstriction.
Hypothermia (a core body temperature below 35°C) happens when heat loss exceeds heat production. Older adults lose heat more easily, and they make less of it when it is cold. A cool room can be enough to let an older person's core temperature fall.
Subcutaneous fat (the layer of fat just beneath the skin) slows the escape of body heat, and older adults often have less of it. Heat therefore leaves through the skin more readily, particularly in a cool room.
Control of vasoconstriction (narrowing of the skin's blood vessels to keep warm blood in the core) is reduced with age, which is linked to slowed production of neurotransmitters (the chemical messengers between nerve cells). Heat is conserved less well. In a cooling experiment, older volunteers began to vasoconstrict and produce heat at lower core temperatures than younger volunteers, and their maximum responses were weaker. Their core temperature therefore fell further before the body reacted.
Shivering (repeated muscle contraction that releases heat) depends on skeletal muscle, and ageing brings loss of muscle mass, so shivering is less effective. Older people may also notice the cold less well and move around less, so they can stay in a cold room without realising. Illness, medicines and a cold home add to the risk, and the effect varies from person to person.
Less active sweat glands are a genuine change with age, but they make cooling in the heat harder. They do not explain heat being lost in the cold.
Key facts
- Definition
- hypothermia is a core body temperature below 35°C.
- Insulation
- older adults often have less subcutaneous fat, so heat leaves through the skin more readily.
- Vasoconstriction
- control of the skin's blood vessels is reduced with age, so heat is conserved less well.
- Shivering
- loss of muscle mass makes shivering less effective, so less heat is produced.
- Sensation and movement
- older people may notice the cold less well and move around less, so they can stay in a cold room without realising.
- Not the explanation
- less active sweat glands make cooling in the heat harder, but they do not cause heat loss in the cold.
Exam traps
- Greater reliance on brown fat (a tissue that makes heat without shivering) characterises newborn thermoregulation, not normal ageing, so it does not explain the risk; older adults still use shivering to generate heat.
- Reduced sweat gland activity is a true change with age, but it limits cooling in hot environments. Sweating is a cooling response that the body does not use against cold, so it does not explain vulnerability to hypothermia.
- A large surface area relative to body mass is characteristic of babies and young children rather than older adults, so it does not describe the age-related change.
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