Page last updated at 08:58 GMT, Tuesday, 30 June 2009 09:58 UK

Why do we succumb to hot weather?

By Michelle Roberts
Health reporter, BBC News


GP Dr Rosemary Leonard gives her top tips to beat the heat

A scorching summer can be idyllic - the promise of unspoilt barbecues and trips to the seaside.

But when temperatures soar, health risks rise.

In August 2003, when temperatures hit 38C (101F) during a nine-day heatwave, the highest temperature recorded in the UK, there were 2,000 to 3,000 extra deaths in England.

Across Europe, the toll was around 30,000.

And climate change means that heatwaves are likely to become more common.

Be prepared

By the 2080s, it is predicted that an event similar to that experienced in England in 2003 will happen every year.

But why exactly are we so vulnerable in a heatwave?

Millions of Brits travel to hot destinations each year and enjoy the sunshine without suffering any ill effects.

We are not as sensible when it's hot at home
Viv Armstrong, chief medical advisor to the British Red Cross

Yet when the hot weather comes to the UK, thousands of us succumb.

Partly it is down to the fact that, as a nation, we are not geared up for good weather.

Our houses don't all have air conditioning or cool marble flooring.

We don't take siestas during the hottest hours of the day.

And when we do get some sunshine, many of us rush outside in our shorts and shades to make the most of the weather.

Viv Armstrong, chief medical advisor to the British Red Cross, said: "When people go on holiday they are prepared for the weather. They pack light clothing and take their sun screen with them.

"Generally they are resting or if they are doing exercise they are reminded by their tour guide to take water with them.

"But we are not as sensible when it's hot at home. We carry on with our daily business in the same way we would if it were cooler weather."

High risk

Experts know that people adapt to temperature during each summer and gradually over long periods of time.

Therefore, the health risks appear to be greater if a heatwave hits earlier in the summer before we have had time to get used to a warm spell.

And in northern parts of England the temperature threshold is lower than for London and the South East.

Increasing temperatures in excess of 23C are associated with excess summers deaths. And the higher the mercury rises, the greater the toll.

During a heatwave it is likely to be hotter in built up cities than in greener surrounding rural areas, especially at night.

In London during the August 2003 heatwave, the maximum temperature difference between urban and rural locations reached 9C on occasions.

Ambient temperature is important because at 27C or over, those with impaired sweating mechanisms find it especially difficult to keep their bodies cool.

Any factor that reduces the effectiveness of sweating, such as dehydration, lack of breeze, tight-fitting clothes or certain medications can cause the body to overheat.

Keep cool

The elderly and the chronically ill are particularly vulnerable because their body's basic temperature control mechanisms may not work as well as it should.

Young children also have a decreased ability to sweat, as well as having a higher core temperature that rises faster during dehydration.

Happens when the body's temperature control fails
Can result in organ failure, brain damage or death
Warning signs include confusion, disorientation and convulsions

Many deaths can be explained by the reduced air quality that comes with hotter temperatures and air pollution, particularly among people with pre-existing lung conditions.

Soaring temperatures also put extra strain on the heart as the body pumps larger quantities of blood to the skin to keep itself cool.

For elderly people and those with chronic health problems this can be enough to cause heart failure.

People who misuse alcohol or drugs or who are very physically active, like labourers or those doing sports, also put themselves at risk of dehydration and ultimately heatstroke.

A peak in homicide and suicide rates during previous heatwaves in the UK has also been observed.

Ultimately, experts say the hot weather can be enjoyed, as long as we are sensible and prepare for it.

And if someone you know feels unwell, get them somewhere cool to rest. Give them plenty of fluids to drink.

If symptoms such as breathlessness, chest pain, confusion, weakness, dizziness or cramps get worse or don't go away, seek medical help.

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