Why water is the hot new cool for summer

It is always a good idea to drink plenty of fluid, but extra vigilance is needed in summer when dehydration can come on alarmingly quickly.

As the mercury continues to rise over the coming months, most of us will be looking for ways to stay cool. And while we all know that drinking plenty of fluid is one of the most effective ways to beat the heat, what are not so widely understood are the details of just how much we need and which fluids are best at keeping us hydrated.

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Forget antioxidants, omega-3 fatty acids and vitamin D; water is without a doubt one of the most important factors in health. While it may not make the headlines as much as other, more popular drinks, it remains vital to human life. Approximately 60 per cent of your body is water, and while other nutrients can take weeks or months to become deficient, not drinking enough water can have a detrimental effect very quickly.

Not only is water crucial for a wide variety of bodily processes, such as removing toxins, carrying nutrients and oxygen to cells and protecting and lubricating organs and joints, it plays a vital role in regulating body temperature and keeping you cool.

Some studies suggest that a proper intake of water not only helps to regulate normal body processes, but may also protect against certain diseases, such as bladder and colon cancer, and may also protect the heart. Research at Loma Linda University in California, indicated that, compared with people who drank two glasses of water per day, men in the study who drank more than five glasses daily reduced their risk of heart attack by 54 per cent. Women who drank the most water also experienced a protective effect, with a 41 per cent lower risk of heart attack.

If you've ever neglected to drink enough fluid on a hot day, no doubt you will be familiar with the early signs of dehydration, including thirst, dry mouth, fatigue, dizziness and headache. Other more serious signs include irritability, rapid heartbeat, seizures and low blood pressure. According to the National Health Service (NHS) in the UK, dehydration begins with a reduction of just 1 per cent in body weight as a result of fluid loss. It occurs when there are simply not enough fluids to replace what's lost through normal bodily processes.

So how much water do you need daily? The answer isn't so simple. Over the years, studies have produced varying recommendations, but what we now know is that optimal hydration depends on a number of factors, such as age, activity level and climate, and varies widely from person to person. It also depends on what type of food you eat. Food can supply up to 20 per cent of your daily fluid requirements and choosing food with a high water content, such as fruits, vegetables and soups, helps to maximise this.

The old adage was to get eight glasses of water per day. And while this remains a good reminder to drink up, it doesn't apply to everyone, since fluid requirements are so individualised. However, the Institute of Medicine in the US recommends general amounts for men and women, advising that men should drink an average of three litres of water and beverages every day, and women 2.1 litres.

People who are pregnant, breastfeeding, physically active, or spend time outdoors in extreme heat, have higher fluid needs and will need to consume more to stay hydrated. The question is, more of what?

When it comes to staying hydrated, you need to consider more than just what quenches your thirst, especially if you're watching your waistline. While all beverages contribute to your daily fluid intake, some are obviously better than others when it comes to health and nutrition.

According to study findings published in The International Journal of Obesity, calories from drinks can have a bigger effect on body weight than calories from food because they are less satisfying. Researchers found that when subjects were given 450 extra calories worth of either sweets or soft drinks every day for four weeks, those eating the sweets reduced their calorie intake from other sources to compensate, whereas those consuming the soft drink made no such change in diet and at the end of the study had gained considerably more weight than the sweet-eaters.

Despite the fact that most health recommendations suggest less than 10 per cent of daily calories come from beverages, they remain one of the biggest sources of hidden calories in the diet. One study found that beverages account for 22 per cent of calories in a typical American diet. Some sweetened drinks can rival a meal in terms of calorie content. Consider this: a large, flavoured chilled coffee can run to upwards of 450 calories per serving, while a 250ml bottle of sweetened fruit juice can deliver more than 250 calories. Fizzy and energy drinks are also culprits; both contain more than 100 calories per serving.

The wide range of beverages available prompted one group of nutrition experts to develop a guide that ranks them by calories, essential nutrients, and evidence for positive or negative health outcomes. Not surprisingly the guide, published in The American Journal of Clinical Nutrition, ranked water as the best beverage choice. According to the report, water provides everything the body needs to restore fluid lost through normal processes, such as breathing and sweating, without any calories.

Next up were tea and coffee, which comes as a bit of a surprise. For years, health professionals have advised that beverages with caffeine in them, such as coffee or tea, shouldn't count towards your daily fluid intake because they were thought to act as diuretics and could increase fluid excretion in the body.

But research is now suggesting otherwise. One study, published in The International Journal of Sport Nutrition and Exercise Metabolism, found that men given caffeine capsules experienced no significant differences in blood or urine measurements to indicate additional fluid losses, or dehydration. When consumed on their own, tea and coffee are both calorie-free beverages packed with disease-fighting flavonoids and antioxidants.

After water, tea and coffee, the guide recommends beverages that contain both calories and nutrients, including low-fat and skimmed milk, and pure fruit and vegetable juice. The least-recommended beverages are those with added sugar that contain little or no nutrients, such as fizzy drinks, energy drinks and flavoured coffee.

So when making choices to stay hydrated, take your cue from the guide and choose calorie-free beverages more often. If you have trouble drinking plain old water, add freshly squeezed lemon or lime juice, or a splash of pure fruit juice to add some flavour.

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