Water Intake

How much water should we drink?

Our bodies are about 60% water. Throughout the day we lose water through our breath, our urine and through perspiration.  So it’s important to avoid dehydration and keep ‘topped up’ through our food and drink as we go through each day.  The amount we need on a daily basis does depend on many factors including where you live in the world and your activity levels.

In the UK the NHS recommends a daily intake of 6-8 glasses of fluid a day irrespective of gender.  This equates to a maximum of about two litres a day.  Tea, coffee, lower fat milk and sugar free drinks all count towards this total.  It’s a good idea to take sips of water regularly throughout the day to stay ‘topped up’.  This is especially important for the over 60’s as your thirst sensitivity declines with age.

The amount of water you actually need depends on many factors:

Your diet:  If you drink a lot of tea and coffee you may lose extra water through their diuretic effects.  A diet high in salty, spicy or sugary foods also requires more water.

Your location:  If you live in a mountainous area or in a hot, dry or humid area you also need more water.

The external temperature:  In the warm seasons the body loses more through perspiration.

Your job:  If your job requires you to work outdoors in the sun or you work in a very warm room you will get thirstier quicker.

Your activity level:  If your job entails a lot of walking or standing around you will need more water than someone with a sedentary desk job.  Intense levels of exercise also require more water to counter the moisture expelled as you breathe faster.

Your health:  If you have sickness or diarrhea you need to  replace lost fluid.  Diabetics also need to drink more.

Pregnant or breastfeeding:  Both conditions require more water for baby.

Eat your water

Mild dehydration can affect mood and energy levels

Studies show that drinking enough to avoid mild dehydration helps support brain function.  Even mild dehydration can affect our ability to solve problems.

A study in China showed that men deprived of water for 36 hours had big effects on fatigue, attention span and focus, reaction times and short-term memory.

Other studies have shown even mild dehydration can affect physical performance.  A study of older, healthy men who had a 1% fluid loss suffered reduced muscle strength, power and endurance.

Another study of women showed a fluid reduction of 1.36% after exercise resulted in impaired mood, concentration and an increase in headaches.

A fluid loss of 1% might not seem much but it’s a lot to lose!  This can happen if you are in a very warm room and sweating a lot.


Water intake and weight management

It is possible for the brain to confuse the  hunger signal with the thirst signal.  This has an immediate impact on weight management because you can be taking on calories your body doesn’t want or need.  So if you are feeling a little hungry have a drink first!

In a study at Virginia State University they looked at fluid consumption and weight.

Two groups were asked to follow the same healthy diet for three months.  But one group was asked to drink 500ml of water half an hour before each meal.

The group who drank the water lost more weight than the group who didn’t.

Both groups were asked to complete 10000 steps a day.  The group who drank the water adhered to the steps rule more than the group who didn’t drink the water.

Other studies have suggested that drinking more water increases the  metabolism and can result in weight loss.  This could be the result of increased energy expenditure due to the thermogenic response.

If you feel that you haven’t been drinking enough water make any upward changes gradually because the body may start to release stored water held as part of the survival mechanism.

Can you drink too much water?

The answer to that is an emphatic ‘yes’.  Our thirst mechanism tells us when we really do need a top up.  But some people believe erroneously that they need more than the body requires.

The 2018 London Marathon was the hottest on record.  The only advice runner Johanna Pakenham says she got was to ‘drink lots of water’.  Nobody advised her to also take care of the electrolyte levels in her body.

She drank so much water during the race she developed over hydration – or hyponatremia  Her friend and partner later gave her a large glass of water which resulted in a fit and her heart stopped.

She was airlifted to hospital and recovered two days later.

Too much fluid consumption can become serious when it causes a dilution of sodium in blood. This creates a swelling of the brain and lungs, as fluid shifts to try to balance out blood sodium levels.  Under normal circumstances the body regulates the water/sodium balance with a very high degree of accuracy.

Our hydration sensors are located in the kidney.  If the kidney senses adverse change – too much or too little water it secretes a hormone called renin.  If the person is dehydrated the thirst signal is activated and at the same time the kidney is instructed to conserve water.  Hence a sign of dehydration is dark urine.

If we have too much water the kidneys are instructed to release more water – hence you pee a lot.