Water balance, importance of good hydration

Water is essential for life, and maintaining hydration is important for physical and mental performance. The human body is largely made of water. Body water content declines with age, from about 75% in babies to 60% in adults. Although we can live for up to 50 days without food, without water we will survive only a few days, even in a cool climate. People generally drink enough water, but for specific population groups, like the elderly, or while exercising, fluid intake might become critical.

Daily water losses

Water leaves our bodies through skin and in breath all the time, amounting to about 700ml each day. We lose another 100ml through faeces, about 1.5 litres as urine and 200ml in normal perspiration. So, even living and breathing in a temperate climate requires about 2.5 litres a day. Exercise and rises in temperature increases perspiration, loss of water and hence fluid requirements. During sickness and diarrhoea, losses of water will also increase considerably.

The effects of dehydration. Dehydration can cause headaches, tiredness and loss of concentration. It is a problem particularly associated with aging, as older adults are less sensitive to mild dehydration, they drink less and take longer to re-hydrate. A deterioration of mental performance can also occur in mildly dehydrated younger adults. Children lose more water in perspiration in trying to keep cool so it is important to make sure they drink enough in hot weather.
Drinking enough to maintain hydration. We should drink enough to balance water losses. The metabolic processes in our bodies produce about 250ml, and we get another 750ml from our food. This leaves 1.5 litres to be supplied from drinks. All water-containing drinks can contribute to the total required for hydration including fruit juice, soft drinks, tea, coffee, dilute alcoholic drinks such as beer, as well as pure water itself. It has been shown that drink palatability is important when fluid requirement is high. Studies have also shown that caffeine in amounts typical of a cup of coffee or tea or a cola drink do not have a dehydrating effect, so experts now agree that normal caffeine containing drinks can contribute to total water requirements. However, drinks containing 10% alcohol or more, such as most wines, do result in net fluid losses.

What happens when we exercise in hot climates?

During exercise our bodies keep cool by evaporating fluid from our skin as sweat, so we must drink more to avoid dehydration. In cold or temperate climates young people can often tolerate a 2% loss of body weight as water without impairment of physical performance, but in the heat this amount of fluid loss will compromise performance and can result in heat illness. Losses in excess of 5% of body weight can decrease the capacity for work by about 30%. A number of studies have demonstrated that maintaining hydration before and during endurance exercise is effective in improving performance in a variety of conditions.

Salt stimulates water absorption and aids retention during and after exercise

Adding sodium (salt) to drinks stimulates carbohydrate absorption and this enhances water uptake. Replacing the salt lost in sweat helps to maintain blood volume. If large amounts of water alone are drunk during and after endurance exercise in the heat, dilution of body fluids may occur, leading to large losses of water in the urine. This means hydration will not be maintained and low sodium levels may cause heat cramps and exhaustion. To prevent this, drinks should contain sodium (as in sport drinks which contain amounts similar to those of human body fluids), or water should be drunk with food.

Path to improved wellness

You should drink water every day. Most people have been told they should drink 6 to 8, 8-ounce glasses of water each day. That is a reasonable goal. However, different people need different amounts of water to stay hydrated. Most healthy people can stay well hydrated by drinking water and other fluids whenever they feel thirsty. For some people, fewer than 8 glasses may be enough. Other people may need more than 8 glasses each day. If you are concerned that you are not drinking enough water, check your urine. If your urine is usually colorless or light yellow, you are well hydrated. If your urine is a dark yellow or amber color, you may be dehydrated.

Water is best for staying hydrated. Other drinks and foods can help you stay hydrated. However, some may add extra calories from sugar to your diet. Fruit and vegetable juices, milk, and herbal teas add to the amount of water you get each day. Even caffeinated drinks (for example, coffee, tea, and soda) can contribute to your daily water intake. A moderate amount of caffeine (200 to 300 milligrams) is not harmful for most people. This is about the amount in 2 to 4, 8-ounce cups of coffee. However, it’s best to limit caffeinated drinks. Caffeine may cause some people to urinate more frequently, or feel anxious or jittery.

Water can also be found in fruits and vegetables (for example, watermelon, tomatoes, and lettuce), and in soup broths.

Sports drinks can be helpful if you are planning on exercising at higher than normal levels for more than an hour. It contains carbohydrates and electrolytes that can increase your energy. It helps your body absorb water. However, some sports drinks are high in calories from added sugar. They also may contain high levels of sodium (salt). Check the serving size on the label. One bottle usually contains more than one serving. Some sports drinks contain caffeine, too. Remember that a safe amount of caffeine to consume each day is between 200 and 300 mg (milligrams).

Energy drinks are not the same as sports drinks. Energy drinks usually contain large amounts of caffeine. Also, they contain ingredients that overstimulate you (guarana, ginseng, or taurine). These are things your body doesn’t need. Most of these drinks are also high in added sugar. According to doctors, children and teens should not have energy drinks.

If staying hydrated is difficult for you, here are some tips that can help:

• - Keep a bottle of water with you during the day. To reduce your costs, carry a reusable water bottle and fill it with tap water.
• - If you don’t like the taste of plain water, try adding a slice of lemon or lime to your drink.
• - Drink water before, during, and after a workout.
• - When you’re feeling hungry, drink water. Thirst is often confused with hunger. True hunger will not be satisfied by drinking water. Drinking water may also contribute to a healthy weight-loss plan. Some research suggests that drinking water can help you feel full.
• - If you have trouble remembering to drink water, drink on a schedule. For example, drink water when you wake up, at breakfast, lunch, and dinner, and when you go to bed. Or, drink a small glass of water at the beginning of each hour.
• - Drink water when you go to a restaurant. It will keep you hydrated, and it’s free.

Don’t wait until you notice symptoms of dehydration to take action. Actively prevent dehydration by drinking plenty of water. Some people are at higher risk of dehydration, including people who exercise at a high intensity (or in hot weather) for too long, have certain medical conditions (kidney stones, bladder infection), are sick (fever, vomiting, diarrhea), are pregnant or breastfeeding, are trying to lose weight, or are not able to get enough fluids during the day. Older adults are also at higher risk. As you get older, your brain may not be able to sense dehydration. It doesn’t send signals for thirst.

Water makes up more than half of your body weight. You lose water each day when you go to the bathroom, sweat, and even when you breathe. You lose water even faster when the weather is really hot, when you are physically active, or if you have a fever. Vomiting and diarrhea can also lead to rapid water loss. If you don’t replace the water you lose, you can become dehydrated.