65% of our bodies consist of water. It is essential for life. So given its importance you would expect there to be a clear scientific answer to the question “How much should I drink a day?” This is not the case as our fluid requirements vary depending on a person’s age, body size, gender, environment and level of physical activity.
We need to ensure there is enough fluid in our bodies to maintain normal function of our heart and our kidneys. To do this we naturally take in the equivalent of approximately 8 glasses of water (2 litres) per day. Children need less and pregnant women need a little more. Most of this fluid is from drinks, but some comes from food, such as soups, stews, fruit and vegetables. In a healthy body, the brain detects when the body is becoming dehydrated and initiates thirst to stimulate drinking. It also releases a hormone which signals to the kidneys to conserve water by concentrating the urine.
Being thirsty is not a sign of anything other than a need to drink and rebalance our body fluids. It is a very sensitive mechanism. When we are unwell, we need to drink more. This is because temperature associated sweating, vomiting and loose stools all cause loss of water. Not passing any urine for 12 hours is a significant sign of dehydration, especially in children.
As we get older our body systems are less finely tuned, the cardiac muscles weaker and the kidneys not as good at keeping everything in physiological balance. Combine this with a more sedate lifestyle and it is normal to experience some collection of water in the lower legs / ankles towards the end of the day. This is best treated by wearing support hosiery. Some patients with heart or kidney conditions actually need to limit the amount of water they take to ensure the system is not overloaded. Doctors might suggest restricting intake to a certain number of drinks per day and will also use water tablets (diuretics) to help achieve a finer balance.
Ultimately, we do not need to be concerned about drinking an arbitrary amount of water per day: our bodies signal to us when we’re thirsty, much like they do when we’re hungry or tired. The only health benefit of drinking more than you need will be the extra calories you expend by running to the loo more often.
So, listen to your body and drink if you are thirsty. Listen to your doctor if they suggest you need to limit how much you drink. If you hear nothing from either of these sources then you can be reassured you have it just right.
Anthony O’Brien, Wyndham House Surgery
Published in Parish magazines April 2023