Water is an essential nutrient, more important to life than any other and required in larger quantities, this is especially true in the summer months when the weather is hot as it is now in the UK.
Let’s remind ourselves why the body can only survive a few days without water, why is it so essential?
Water makes up around 60% of the body weight of an adult, and even more of a child’s, it makes up around 75% of lean tissue weight and less than 25% of body fat. Older adults, women, and those living with obesity generally have a smaller proportion of water due to having less lean tissue.
Outlined below are a number of life processes that water plays an essential role.
In order for these and many other functions to take place within the body there needs to be a water balance, where intake = output. Bodily fluids consist of those inside cells (intracellular), outside the cells (extracellular), between cells (interstitial) and inside blood vessels (intravascular). The entire system of cells and fluid are in a constant state of homeostasis, where fluids are lost and replaced under the control of the hypothalamus within the brain.
Thirst and satiety signalling from the hypothalamus, mouth and nerves allow the person to seek water, older adults find this harder as the message is harder to perceive, this can lead to a risk of dehydration; water balance disrupted.
The body excretes around 500ml of water each day as urine to dispose of metabolic waste products. Other water losses occur from the skin via sweat (450ml – 600ml) depending on the environment and physical activity level, the lungs as vapour (350ml) and the GI tract via faeces (150ml). On average the total daily water loss is around 2.5 litres. This output is balanced by water intake from liquids (500 – 1500ml), food (700-100ml) and metabolic water (200-300ml).
This balance is delicate and requires healthy kidneys and an adequate intake of fluids, next week I will cover water recommendations to ensure optimum health.
References
Whitney et al (2014) Understanding Nutrition 2nd Edition
MLT Nutrition 