The Bottom Line: Do you need to drink eight glasses of water a day?

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SINGAPORE – In the recent weeks of hot and humid weather, have you been having headaches, feeling cranky or dealing with constipation? Then you may not be drinking enough water, say doctors, as these are common symptoms of dehydration.

 

Many people have heard that one needs to drink eight glasses of water a day. However, doctors say this amount is an oversimplification and may not meet a person’s daily water needs.

 

It is also not enough to rely on thirst to signal when you need to replenish your fluids.

 

Dr Lim Lee Guan, a gastroenterologist at Mount Elizabeth Hospital, says: “Thirst is not always a reliable early indicator of hydration status. Many people, especially the elderly, may not feel thirsty until they are dehydrated.”

 

Essential to health

 

Water is essential for the body’s functions, with up to 60 per cent of an adult human body being made up of water, say doctors.

 

Water is needed to carry out activities such as digestion, regulating body temperature and ensuring that cells receive nutrients and oxygen.

 

Dr Anita Elangovan, a family physician at Raffles Medical, says that a person loses water through breathing, perspiring and urination.

 

“The amount of water required varies according to a person’s age, body size, health and activities, and the weather,” she adds.

 

“In hot weather, our body loses more water through perspiration. This loss of fluid should be replaced by drinking more than the recommended eight glasses of water for normal adults.”

 

She adds: “This is similar to when we exercise or are unwell with symptoms such as fever or diarrhoea, where fluid intake should be increased to replace the lost fluids. Otherwise, dehydration can set in, which is more dangerous in young children and older adults.”

 

Dr Jay Lim, a urologist at PanAsia Surgery Group, sees many patients with kidney stones and urinary tract infections caused by dehydration.

 

“In most cases, working adults are likely to neglect their hydration due to their busy schedules. Busy mothers with young children often report a lack of adequate hydration, and coupled with holding their urine, this adult group is also most susceptible to poor drinking habits.”

 

He and other doctors recommend water as the best fluid to keep oneself hydrated. They suggest avoiding drinks containing alcohol and caffeine, as these are diuretics which lead to more frequent urination and thus increase fluid loss.

 

How much water to drink

 

Parkway Shenton’s medical director Edwin Chng says that, in general, men should drink about three to four litres a day and women should drink two to three litres a day, depending on factors such as their body size, level of physical activity and exposure to warm climate.

 

One litre is about four glasses of water.

 

“One should drink enough to urinate several times a day, and the urine should be pale and odour-free. If an individual is pregnant, unwell, not eating well, exercises more than the average person, perspires a lot, especially in the current hot weather, or if the urine is dark-coloured or smells, he or she needs to increase the water intake,” he says.

 

The humidity in Singapore sends the body into “overdrive” when it comes to sweating, adds Dr Chng. “In high humidity, the air is nearly full of water vapour and it is difficult for sweat to evaporate. In an attempt to cool itself, the body goes into overdrive and continues to sweat and sweat. Hence, a higher water intake is required to replace the increased water loss through sweating.”

 

Dr Lim Lee Guan says a person could lose up to 10 litres of water a day through sweat. The actual sweat rate depends on a person’s metabolic rate, or the amount of energy expended by the body in staying alive.

 

He suggests multiplying your body weight in kilograms by 30 and 40 to get an estimate of how many millilitres of water you require a day. A 60kg adult would thus require at least 1.8 to 2.4 litres of water a day.

 

He notes that both Singapore’s Health Promotion Board and Britain’s National Health Service recommend drinking eight glasses of water, or two litres, a day. This amount includes water from food and liquids such as low-fat milk and sugar-free drinks.

 

However, people with medical conditions such as heart failure, kidney failure and liver failure will need to consult their doctors for an individual recommendation of what to drink and eat, as they are at risk of a condition known as fluid overload.

 

“This can lead to fluid in the lungs causing breathing difficulty, fluid in the abdomen causing abdominal distension and fluid in the limbs causing swollen limbs,” he says. “In addition to fluid restriction, salt restriction is usually also required. The doctor will advise on the restriction needed based on the individual’s condition.”

 

When to drink water

 

Doctors say people should not rely on feelings of thirst as a signal of when they need to replenish their fluids. Many might feel grumpy or cranky or develop a headache – all signs of dehydration – and not notice that they are thirsty.

 

Dr Anita says: “It is important to ensure adequate fluid intake, and not consume water only when you are feeling thirsty. One way to go about this will be to consume water with meals.”

 

Children and seniors are at higher risk of dehydration, she adds. Children are more likely to be outdoors and exercising in hot weather, while older adults may have a decreased sensation of thirst or decreased kidney function.

 

“Older adults are also more likely to have chronic medical conditions that can cause fluid loss like uncontrolled diabetes or bladder issues such as incontinence. They could also be on medications that result in frequent urination and hence fluid loss,” she says.

 

Parents and caregivers should monitor children and seniors for symptoms of dehydration such as tiredness, dizziness, headaches, crankiness, constipation, decreased urine output or dark-coloured urine.

 

In the case of such symptoms, increase fluid intake, ensure the person is kept cool and seek medical attention if necessary.

 

Dr Jay Lim suggests a measured approach to drinking water since people are “relatively poor at gauging fluid volume”. He advises choosing a water bottle with a known volume, drinking from it and refilling it to ensure that you meet your daily water needs.

 

He says: “Avoid excessive fluid intake in the early morning or evenings after work, as waking up at night to empty your bladder regularly affects sleep quality.”

 

The Bottom Line: Adults in Singapore without medical conditions may need more than eight glasses of water a day, based on body size and physical activity. Rather than monitoring thirst, monitor the colour and odour of your urine to check whether you are drinking enough. Increase your fluid intake if your urine smells bad or is dark.

 

• The Bottom Line is a series which aims to answer burning questions on health and well-being.

 

 

Source: The Straits Times © SPH Media Limited. Reproduced with permission.

 

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