Heat and cold: why older bodies regulate temperature badly

Excess mortality during temperature extremes is concentrated almost entirely in older adults. The 2003 European heatwave produced an estimated 70,000 excess deaths, the overwhelming majority in people over seventy-five. Cold-related excess winter mortality follows a similar age distribution in most temperate countries.

The reasons are physiological, pharmacological and social, in roughly equal measure.

Why heat is harder to handle

Sweating capacity declines. Sweat gland output falls with age and the threshold at which sweating begins rises, so cooling starts later and proceeds more slowly.

Skin blood flow response is blunted. Dumping heat requires shunting blood to the skin, and this vasodilatory response is reduced.

Cardiac reserve is lower. Cooling in heat demands increased cardiac output, which is precisely what a person with heart failure or ischaemic disease cannot supply.

Thirst is blunted and kidneys concentrate urine less well, so dehydration develops more readily.

Medications interfere. Diuretics increase fluid loss. Anticholinergics reduce sweating. Beta blockers limit the cardiac response. Some antipsychotics impair thermoregulation directly. SGLT2 inhibitors increase fluid loss.

Perception is poorer. Older adults are demonstrably less accurate at judging ambient temperature and less likely to take action in response.

Practical heat protection

Most of it has to be arranged in advance, because the people most at risk are the least likely to act during the event.

Keep windows and curtains closed during the hottest part of the day and open at night when the air is cooler. Identify the coolest room in the house and use it. Fans help below about 35°C; above that, moving hot air over the skin can increase heat gain, and damp cloths or a cool shower are more effective.

Increase fluid deliberately rather than in response to thirst. Anyone on diuretics should have a clear instruction from their prescriber about whether the dose needs temporary adjustment — this is a decision for the clinician, not the patient, and it is worth asking about before summer rather than during a heatwave.

Store medicines below 25°C; several, including insulin and some inhalers, degrade in heat.

And check on people. Living alone is one of the strongest risk factors in every heatwave mortality analysis.

Cold

The mechanisms mirror the heat ones. Shivering response and vasoconstriction both diminish. Metabolic heat production falls with reduced muscle mass. Perception of cold is less accurate. And reduced mobility means less movement to generate heat.

Cold also affects the cardiovascular system directly: blood pressure rises, blood viscosity increases and platelet aggregation is enhanced, which is part of why myocardial infarction and stroke rates rise in winter. Cold air provokes bronchoconstriction in asthma and COPD.

Hypothermia — core temperature below 35°C — can develop indoors, slowly, over days, in a poorly heated home. It presents as confusion, drowsiness, slurred speech and clumsiness rather than as obvious shivering, since shivering stops as hypothermia deepens. It is regularly mistaken for a stroke or for dementia.

Practical cold protection

Heat the main living room to around 18–21°C during the day and keep the bedroom at a similar temperature at night. The World Health Organization recommends a minimum of 18°C for older or vulnerable people.

Several thin layers work better than one thick one. Hats and warm socks matter more than people expect. Hot drinks and regular hot meals contribute both energy and warmth.

Keep moving indoors — even light activity every hour generates heat and maintains circulation.

Fuel poverty is a substantial driver of cold-related harm, and many older people ration heating for financial reasons while telling nobody. Winter fuel support schemes exist in most countries and are consistently under-claimed. Insulation and draught-proofing grants likewise.

The wider point

Both heat and cold events are largely predictable, and both kill people who were doing exactly what they always do. The interventions that work are unglamorous — a fan bought in May, a thermometer in the bedroom, a neighbour who knocks, a medication review before summer, a benefits check before winter.

If you are checking on someone during a heatwave or a cold snap, ask what the room temperature actually is rather than whether they feel all right. Their answer to the second question is, physiologically, not very reliable.