Water is essential for human life. It accounts for for 50-70 percent of our body weight and is crucial for most bodily functions. Any deficit in normal body water – through dehydration, sickness, exercise or heat stress – can make us feel rotten. First we feel thirsty and fatigued, and may develop a mild headache. This eventually gives way to grumpiness, and mental and physical decline.
We continually lose water via our breath, urine, faeces and skin. Most healthy people regulate their body’s water level remarkably well via eating and drinking, and are guided by appetite and thirst. But this is more difficult for infants, the sick, the elderly, athletes, and those with strenuous physical occupations, especially in the heat.
What happens when you dehydrate?
By the time you feel thirsty your body is already dehydrated; our thirst mechanism lags behind our actual level of hydration. Research shows that as little as 1 percent dehydration negatively affects your mood, attention, memory and motor coordination. Data in humans is lacking and contradictory, but it appears that brain tissue fluid decreases with dehydration, thus reducing brain volume and temporarily affecting cell function.
As you ‘lose’ body water without replacing it, your blood becomes more concentrated and, at a point, this triggers your kidneys to retain water. The result: you urinate less. The thicker and more concentrated your blood becomes, the harder it is for your cardiovascular system to compensate by increasing heart rate to maintain blood pressure.
When your dehydrated body is ‘pushed’ – such as when exercising or faced with heat stress – the risk of exhaustion or collapse increases. This can cause you to faint, for instance, when you stand up too quickly. Less water also hampers the body’s attempts at regulating temperature, which can cause hyperthermia (a body temperature greatly above normal). At a cellular level, ‘shrinkage’ occurs as water is effectively borrowed to maintain other stores, such as the blood. The brain senses this and triggers an increased sensation of thirst. Source: Here’s what happens to your body when you’re dehydrated This article was written by Toby Mündel from Massey University, and was originally published by The Conversation.