By Zhu Linyong (China Daily)

Photos By Jonah M. Kessel / China Daily

Good drinking habits will help you keep fit and healthy during the scorching summer heat. Zhu Linyong reports

When the weather is extremely hot, your body may not adjust well to the high temperature or humidity changes. This can be exacerbated if you are in the sun or if there is little wind. There have been many reported cases of people collapsing from dehydration and heat stroke, or people getting sick in Beijing and other cities over the past weeks.

Cheng Yiyong, director of China Nutritionists Association, offers tips for people to keep hydrated and avoid health risks on scorching summer days.

'Wherever you go, carry a bottle of water; drink plenty of water throughout the day, even if you do not feel thirsty,' Cheng says.

Due to high temperatures and rising humidity, normal activities like walking to the office or school can leave one sweating.

'The more time you spend outside, the more water you need to replenish lost fluids,' Cheng notes.

Excessive loss of water due to extreme heat and humidity can be potentially life threatening, Cheng warns.

'Extreme heat and humidity rob the body of water through perspiration, which disrupts the body's natural balance since water is responsible for dispersing nutrients throughout the body while expelling toxins.'

How much to drink?

On hot summer days, an adult needs to drink at least 1,500 ml to 3,000 ml of water per day to keep the body functioning normally.

But most people drink far less than that amount, Cheng points out.

Besides oxygen, it is the most important nutrient in the body, functioning as a physiological 'jack of all trades'.

'By the time you feel thirsty, you probably have already lost lots of your total body water,' Cheng says. 'However, this is a common mistake people make.'

Low-volume water drinkers may have dry, itchy skin or feel tired and groggy when they wake up or at mid-day, typical signs of dehydration; longer-term, more serious dehydration presents more serious problems, dangerously affecting blood pressure, circulation, digestion, kidney function and nearly all body processes, Cheng says.

People are likely to buy bottled or canned drinks when they are out in the sun.

'It is a personal choice when one faces a wide range of heavily marketed sports drinks, diet drinks, energy drinks, cola and regular soft drinks,' says Cheng, the chief editor for The Guidebook for Chinese People's Foods and Beverages.

Most of these drinks contain caffeine and sugar. But scientific research have shown that caffeine and alcohol act as diuretics, causing the body to lose water through increased urination.

Still, studies over the past years have showed an association between increasing consumption of sugar-sweetened drinks and weight gain as well as obesity among children and adults. And carbonated soft drinks and fruit juices that are high in sugar can adversely affect blood sugar.

Also, in the June 2009 issue of the International Journal of Clinical Practice, doctors issued a warning about excessive cola intake.

Although further studies are needed to establish how much is too much when it comes to the daily consumption of cola drinks, Dr Moses Elisaf from the department of internal medicine at the University of Ioannina, Greece says: 'There is increasing evidence to suggest that excessive consumption of any kind of cola can lead to a range of health problems including fatigue, loss of productivity and muscular symptoms that vary from mild weakness to profound paralysis.'

Even coffee and tea contain caffeine, which has a diuretic effect and makes one lose water.

Therefore, in Cheng's view, 'boiled, plain water (or genuine, natural mineral water which is rare to find nowadays) is always the best for hydration and people of all ages need to drink plain water.'

However, Cheng advises people not to drink too much purified water, as it is 'safe, but too clean to contain enough nutrients especially the minerals the body urgently needs on hot days.'

An imbalance or lack of important minerals, including calcium, magnesium, sodium, and potassium, can cause problems with a person's heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils, and urination, says Cheng.

Cheng recommends fresh fruits such as watermelon and traditional drinks such as mung bean soup and milk.

When to drink?

'One must drink 300-450 ml of water after waking up in the morning,' says Shen Yanying, a nutrition consultant with Beijing Chaoyang Hospital.

During the night, the human body consumes over 300 ml of water.

'Drinking at this time helps boost blood circulation, prevents cardiovascular diseases, cleans up the urinary system, and prepares the digestive system for breakfast,' she explains.

To stay hydrated, one ought to drink a similar quantity of water after doing sports in the sun or taking a shower.

'When drinking, drink it slowly; don't drink large quantities of fluids at one time and try not to drink too quickly. The human body needs time to gradually absorb the water,' Shen says.

Shen also advises people not to drink too much cold water, with a temperature below 15 C, so as to avoid stomachache or diarrhea.

While hot, dry weather can cause a lot of sweat loss, cloudy, humid weather can also be dangerous.

So, one must drink the same amount of water as on a hot, sunny day, says Fan Zhihong, nutrition and food safety professor with China Agriculture University.

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