thirst and rehydration

Beat the heat, correctly DR GITA MATHAI Summer is here in full force and advertisements for fizzy drinks, colas, sports drinks, beer (surrogate advertising) and even plain glucose have started flooding prime time television. They claim to quench your thirst, give a much needed energy boost and improve flagging sports performance. Everyone needs adequate fluid and electrolytes in summer, to replace the visible amounts lost as sweat and the unseen lost as evaporation from the body. In hot and humid climates, the fluid loss may go unnoticed till the body signals dehydration with thirst, a parched mouth, headache, nausea and muscle cramps. Urine may become scanty and darker. If these symptoms are ignored, dehydration can proceed to heat exhaustion or heat stroke, with the temperature rising to 104°F or more, dry flushed skin with no sweating, delirium, loss of consciousness and even seizures and death. Healthy adults recognise the symptoms of thirst and proceed to drink water. Those over 65 may not recognise the symptoms or ignore them. They may also be more vulnerable if they are on medication like beta blockers or anti depressants. These affect the body’s ability to stay hydrated. Infants are unable to express themselves when they are thirsty. They also lose more fluid as their exposed body surface is greater than in adults. Some, though not all, may stick out their tongue in a serpentine movement if they are thirsty. Parents and caregivers need to recognise their need and offer fluids at frequent intervals. A child that is not thirsty will refuse the fluid. School going children may become engrossed in play and ignore thirst. They need to carry at least a litre of water with them to school. Even while playing in the compound, they should carry water. Fluids that are “isotonic” and contain water and electrolytes in the correct proportions replenish body fluids. Many advertised fruit drinks, colas and reconstituted powders are “hypertonic”. The body loses fluid from its cells into the stomach as it tries to make them isotonic and utilisable. Thirst is aggravated instead of being quenched. Sugar or plain glucose is often added to drinks. Since the body requires glucose for metabolism, this should in theory provide the body with an instant energy boost and quench thirst. If the drink is isotonic (some sports drinks are), the extra glucose will provide a temporary energy boost. After an hour, in some people there is a rebound effect with increased thirst, fatigue and drowsiness. The instant calories also prevent the body from efficiently breaking down its fat stores, negating the effect of exercise on weight loss. Although ice water may appear refreshing, the body has to expend energy to bring the water to room temperature before it is absorbed. Fluid at room temperature is absorbed faster. Fluids should be drunk before thirst sets in so that you never become dehydrated. Adult men need around three litres of water a day and women around 2.5. Children need 100ml/kg until they are 10kg. Over 20kg they need 1,000ml (1 litre) plus 50 ml/kg. This is the baseline requirement. Activity requires additional fluid; adults need 300ml for every 20 minutes and children 200ml. Fluid needs do not stop when the activity is over. Around 500-600ml needs to be drunk after activity. A mouthful of liquid for an adult is roughly 30ml and a child’s 15ml. If you are rarely thirsty and pass around 1.5 litres of urine a day, your hydration is probably adequate. Plain water is best for rehydration. Lightly salted butter milk, lime juice or coconut water are also effective. Ready mix drinks and sports drinks should be either avoided (unless you are an endurance athlete) or used judiciously. If a person has heat exhaustion: nBring them indoors to a shady place and switch on the fan Give them fluids Place ice in the armpits and groin Swab them with a towel soaked in water at room temperature. Allow the water to evaporate Dr Gita Mathai is a paediatrician with a family practice at Vellore. Questions on health issues may be emailed to her at yourhealthgm@yahoo.co.in