After weeks of watching the mercury go up and down, it looks like warm weather has finally come to Britain – and is sticking around.
And, as the Met Office warn that next week could bring the hottest June day on record, there’s never been a better time to learn the warning signs of dehydration.
Research shows that the average UK adult drinks less than half of the recommended water intake per day, risking dehydration – and with it swathes of debilitating health issues.
Dehydration is defined as losing more fluids than you take in, and can be caused by diarrhoea, sweating, drinking alcohol, having a high temperature or spending a long time in the sun.
Drinking water is by far the easiest way to stay hydrated, and the NHS recommends that the average adult should drink between six and eight mugs – or 1.5 to 2 litres – per day.
Yet with many Britons falling short, experts are warning of the dangerous problems that dehydration can lead to, and the signs to watch out for.
Stavros A Kavouras, a professor of nutrition and director of the Hydration Science Lab at Arizona State University, told The Telegraph: ‘Proper hydration aids digestion, supports kidney and heart health, and enhances physical performance.’
So, with that in mind, these are the warning signs of dehydration – and some might surprise you.
The average UK adult drinks less than half of the recommended water intake per day
Being parched
The most obvious sign of dehydration is simple: thirst.
We’ve all been desperate for a drink of water after a long period without, and that is the first sign of dehydration.
According to Dileep Lobo, a professor of gastrointestinal surgery at University of Nottingham and specialist in fluid and electrolyte balance, losing two per cent of body weight in water – through sweat, urine, stools and even breathing – triggers the brain to feel thirsty.
As warmer weather increases sweating, feelings of thirst become more common during the summer months.
The good news is that staying hydrated is straightforward.
Water remains the easiest choice, but experts also recommend drinks containing electrolytes, which can help support kidney function and replenish minerals lost through sweating.
Feeling stressed or less happy
The problems caused by dehydration may not stop with physical health, according to research which has found it may even impact our mental health.
A study in the Journal of Applied Psychology, published last year, found that people who don’t drink enough water may be more likely to feel stressed.
Researchers from Liverpool John Moores University discovered that those who drank the recommended 1.5 litres per day had lower levels of cortisol – the stress hormone in the body – than those who failed to reach the target.
Earlier research, published in the journal PLOS One in 2014, also suggested that hydration has an affect on happiness.
The study examined the effects of both increasing and decreasing water intake among adults and found that participants felt less calm, less content and more tense when they drank less water.
In comparison, those who had an increased water intake reported feeling happier.
The hot weather can make people more dehydrated by increasing the amount they sweat
Darker or smelly urine
Another easy way to check if your body is dehydrated is by checking the colour of your urine.
The NHS uses a simple colour chart to help people assess their hydration levels. Urine that is pale yellow or almost clear is generally considered a sign of good hydration, while darker shades of yellow or brown can indicate that you need to drink more fluids.
This change in colour occurs because the body has less water available to dilute urochrome – the natural yellow pigment in urine.
As dehydration worsens, urine becomes more concentrated, causing it to appear darker.
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Urine also tends to have a stronger ammonia-like smell when a person is dehydrated.
However, dark or unusually strong-smelling urine is not always caused by dehydration.
In some cases, it can be linked to medications, diet, infections or other underlying health conditions. If it persists despite drinking more fluids, medical advice should be sought.
Difficulty making decisions or concentrating
The human body is around 60 per cent water – and the brain even more so, estimated to be up to 75 per cent.
So it is little surprise that being dehydrated can negatively impact cognitive function.
Lewis James, a reader in human nutrition at Loughborough University, says ‘even a low level of dehydration can reduce cognitive skills’ such as memory, attention and co-ordination.
This can also even affect someone’s decision making down to when it is safe to cross the road, he adds.
These symptoms are often grouped under the term ‘brain fog’, which describes mental sluggishness that can make it hard to focus, process information and retain information.
Having a sore head
No advice is more common when someone has a headache than to drink some water – but there is good reason.
It is estimated that the body loses between 2 and 2.5 litres of water per day, and the lack of fluids can trigger severe headaches if not replenished.
Experts believe the lack of water in the brain puts pressure on the pain receptors and nerves, which rehydration eases.
Most headaches as a result of dehydration alleviate within an hour or two of drinking water, but staying out of the sun and keeping cool is recommended to speed up the process.
Research published in the Journal of Clinical Neuroscience found that water can also reduce the pain experienced during migraines – severe headaches which can also be caused by dehydration.
Being tired
A YouGov survey in 2022 found that one in eight Britons report feeling tired all the time, but dehydration may be playing a part.
Experts say that because the body loses fluids through the day, the heart has to work harder to maintain blood pressure and ensure oxygen levels stay normal.
This can leave people feeling sluggish, fatigued and lacking in energy.
Professor Lobo says these symptoms can be felt more keenly in older people who are dehydrated.
He explained: ‘An 80-year-old who weighs 40kg (88 lb) and loses bodyweight through fluids is more likely to feel the effects. Our research shows that older adults, admitted to hospital with dehydration, stay in for longer and have a 6 per cent higher mortality rate.’
Feeling dizzy and faint
Dizziness or lightheadedness is another common warning sign that the body may be running low on fluids.
Professor Lobo warns that losing four per cent of body weight through fluid loss can put people at risk of overheating.
Once this happens, blood pressure drops – leading to feelings of dizziness and, in some cases, fainting.
Dehydration is a recognised trigger for fainting, which happens to around two in five adults at some point in their lives.
The NHS advise that drinking plenty of water, as well as reducing caffeine and alcohol intake – which can dehydrate the body – are among the lifestyle changes that can reduce the chance of fainting.
Cramping up
It is thought that around one third of over 60s struggle with leg cramps – an excruciating pain that can last from a few seconds to 10 minutes.
And official NHS guidance suggests that dehydration may be one of the reasons for it.
The health service advises: ‘In some people, low levels of water in the body can lead to a drop in your salt levels, which can trigger muscle cramps.’
Sodium – the mineral alongside chloride which forms salt – is one of the electrolytes lost through dehydration, which is why experts believe there is a link to cramping.
