Heat waves: what do they do to the body and who is at risk?

By James Gallagher
Health and Science Correspondent

source of images, Getty Images

Authorities warn that high temperatures in the coming days could affect people’s health. The UK Health Security Agency has published a level three alert for the South of England for Friday and Saturday.

Forecasters expect temperatures to reach 28C (82F) on Wednesday across the Midlands and southeast England, although cooler weather is likely further north.

On Friday, London could see 34C (93F) and Manchester 30C (86F).

In this unusually hot weather, people are urged to keep a close watch on the most vulnerable, such as the elderly who are most at risk of heat exhaustion.

Here’s what you need to know about the effects of heat on the body and how to stay cool.

What does extreme heat do to our bodies?

As the body heats up, the blood vessels open up. This causes blood pressure to drop and forces the heart to work harder to push blood throughout the body.

This can cause mild symptoms such as an itchy rash or swollen feet as blood vessels leak.

At the same time, sweating leads to the loss of fluids and salt, and most importantly, the balance between them in the body changes.

This, combined with the lowered blood pressure, can lead to heat exhaustion. Symptoms include:

  • dizziness
  • nausea
  • fainting
  • confusion
  • muscle cramps
  • headache
  • profuse sweating
  • fatigue

If blood pressure drops too much, the risk of heart attack increases.

Why does our body react like this?

Our body strives to maintain a core temperature of around 37.5°C whether we are in a snowstorm or a heat wave.

This is the temperature at which our bodies evolved to work.

But as the weather gets warmer, the body has to work harder to keep its core temperature down.

It opens more blood vessels near the skin to lose heat to our surroundings and starts sweating.

As sweat evaporates, it greatly increases the heat lost through the skin.

How can I stay safe in the heat?

The UK Health Safety Agency has some advice:

  • Be wary of people who have trouble staying cool, such as the elderly, people with underlying medical conditions, and those who live alone
  • Stay cool indoors by closing the curtains in rooms that face the sun
  • Drink plenty of fluids and don’t drink too much alcohol
  • Do not leave anyone, especially babies, young children and animals, in a locked vehicle
  • Do not go out in the sun between 11 a.m. and 3 p.m. when the sun’s rays are strongest
  • stay in the shade, wear sunscreen and wear a wide-brimmed hat
  • Avoid physical exercise in the hottest part of the day
  • Take water with you if you travel
  • Be aware of hidden dangers in rivers and open waters so tempted to calm down

How can I get a good night’s sleep?

Use thin sheets, chill your socks in the fridge before putting them on, and stick to your regular bedtime routine, experts say.

What should I do if I see someone suffering from heat exhaustion?

If they can be cooled in half an hour, heat exhaustion is normally not serious.

  • Move them to a cool place.
  • Have them lie down and raise their feet slightly
  • Have them drink plenty of water – sports or rehydration drinks are also acceptable
  • Cool their skin – spray or sponge them with cold water and fan them. Cold compresses around the armpits or neck are also good

However, if they do not recover within 30 minutes, what follows is heat stroke.

This is a medical emergency and you should call 999.

People with heat stroke can stop sweating even if they are too hot. Their temperature may exceed 40°C and they may have convulsions or lose consciousness.

source of images, Getty Images

People should drink enough water to keep cool

Who is most at risk?

Old age or certain long-term conditions, such as heart disease, can make people less able to cope with the stress that heat puts on the body.

Diabetes can lead to more rapid water loss, and some complications of the disease can impair blood vessels and the ability to sweat.

Children and those who are less mobile may also be more vulnerable. Brain diseases, such as dementia, can also make it difficult for people to notice or do nothing about the heat.

The homeless will also be more exposed to the sun. Those living in top-floor apartments will also face higher temperatures.

Do certain drugs increase the risk?

Yes, but people should continue to take their medication as normal and should try harder to stay cool and hydrated.

Diuretics – sometimes called “water pills” – increase the amount of water the body expels. They are taken widely, including for heart failure. At high temperatures, they increase the risk of dehydration and imbalance of key minerals in the body.

Antihypertensives – which lower blood pressure – can combine with blood vessels widening to deal with the heat and cause dangerous drops in blood pressure.

Some drugs for epilepsy and Parkinson’s disease can block sweating and prevent the body from cooling down.

And other drugs like lithium or statins can become more concentrated and problematic in the blood if there is too much fluid loss.

Does heat kill?

There are around 2,000 deaths caused by high temperatures in England each year.

Most of them will be heart attacks and strokes caused by the exertion of trying to keep body temperature stable.

The higher death rate begins to show once the thermometer passes 25C-26C.

However, evidence suggests that deaths tend to be caused by higher temperatures in spring or early summer rather than ‘peak summer’.

This could be because we start to change our daily behavior as the summer progresses and we become more accustomed to dealing with the heat.

Evidence from previous heatwaves is that the increase in deaths happens very quickly – within the first 24 hours of the heatwave.

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