Eight glasses a day. That’s been the experts’ advice for years. But now, some are rethinking that figure. Dietitian Brooke Longfield looks at how to tell you’re dehydrated.
By the time you’re feeling thirsty, you’re probably already dehydrated. Water accounts for around 50 to 60 per cent of our body mass, and a loss of just one to two per cent of that signals dehydration, which can disrupt healthy body functions. Don’t ignore the early warning signs.
Spot the signs of dehydration
- Dry mouth: Perhaps the most obvious sign of feeling thirsty, this is a reminder that your body needs water. Rather than ignoring it, replenish your body with a refreshing glass of aqua.
- Dark-coloured urine: If you’re healthy and well hydrated, your urine should be a pale straw colour. Dark yellow or amber-coloured urine means you need to drink more.
- Fatigue: Most of us put this down to stress or being under the pump with a heavy workload, but tiredness and lethargy can also be symptoms of dehydration.
- Sallow skin: Long-term dehydration can lead to dry, flaky and wrinkled skin. The more you drink, the better the blood supply to your skin, which results in a healthy, glowing complexion.
- Headaches: The brain is about 80 per cent water, so a telltale indicator that you’re dehydrated is a subtle headache. Before you take that painkiller, try quenching your thirst.
The juice of life
Water is what helps keep our blood circulating. Given blood is 90 per cent water, if you aren’t drinking enough, your circulation becomes sluggish, making it less effective at providing your cells with oxygen. This means no part of your body functions as well as it could.
You know that fuzzy, vague feeling you sometimes get at the end of the day? This can be caused by dehydration. Water lubricates the pathways between brain cells, so when the brain doesn’t get an adequate supply, you may have trouble concentrating.
Water also helps with digestion and prevents constipation. This can be a problem during the summer months, when we sweat more and sometimes drink less. Without sufficient water, foods high in fibre become difficult to digest, resulting in hard, difficult-to-pass stools.
Our bodies are constantly losing water — around 1.5 litres a day in urine (of course, that depends on how much water you drink) and around 200ml through perspiration, with more on hot days, as this is the way the body cools its internal temperature.
We also lose water when exercising. During high-intensity exercise, a person can lose up to 2 litres of water in just one hour! However, low to moderate exercise results in minimal loss so unless it’s an extremely hot day, you probably don’t need to carry a water bottle with you on a gentle walk.
Perhaps less obvious, the simple act of breathing results in a considerable amount of water loss. Every breath you expel is a little water lost. Think of a cold morning when your breath looks like steam — this is water leaving your body and condensing into vapour.
This explains why we usually wake up in the morning weighing a little less and feeling thirsty.
Surprising causes of dehydration
- Stress: When we’re feeling exhausted and under pressure, stress can disrupt the production of the hormone aldosterone. This hormone helps regulate your fluid and electrolyte levels.
- Herbal supplements: Herbal supplements such as dandelion, parsley and celery seed increase urine production and are used to treat fluid retention. Excessive use can cause dehydration, so watch the dosage.
- Breastfeeding: Breastfeeding mums need an additional 700ml (nearly three cups) of water a day to replace the fluid lost in breast milk. A good idea is to keep a glass of water or a water bottle close by to drink while feeding baby.
- Irritable bowel syndrome (IBS): Diarrhoea is a common symptom of IBS and can cause dehydration. In fact, any gastro upset can. So it’s vital to drink plenty of water or even an electrolyte-replacement drink such as Hydralyte to counter this.
- Diabetes: Excessive thirst is one of the symptoms of untreated diabetes. When blood-sugar levels rise, the kidneys try to remove excess glucose by producing more urine. This removes increasing amounts of water from the body, leading to thirst and dehydration.
How much is enough?
As a general rule, men need to replace around 2.6 litres (about 10 cups) of water a day, and women need 2.1 litres (about eight cups). This is where the rule of thumb about drinking eight glasses of water a day comes from. But remember, it is just a guide. Individual needs can vary quite widely.
Also, we take in a surprising amount of fluid through the food we eat. Foods such as grapes, lettuce and watermelon are obvious examples. But even seemingly dry food like bread contains water, while foods cooked in water, such as rice or pasta, also add to your daily target. It’s estimated that the body gets around 20 per cent (between one and two cups) of its total water requirement from solid food alone, but exactly how much your daily diet contributes to your fluid intake is hard to calculate, so consider it more of a bonus to your hydration.
A natural flush
There is an element of truth in the claims of detox advocates who say drinking plenty of water helps flush out toxins. Our kidneys remove some of the toxic waste that is a by-product of our metabolism. These impurities are flushed out in our urine. A well-hydrated person has light-coloured urine that signifies a lower concentration of toxins. Darker urine indicates the kidneys are holding onto fluid and that toxins are building up.
Water also helps keep our bowels moving regularly, which is another way our body rids itself of waste. So, a little extra water helps you feel better on the inside, too.
Is it possible to drink too much water?
Hyponatraemia is the rare condition in which someone has too much water in their system. Excessive water can lead to the body’s sodium levels falling dangerously low. This can cause all the cells to swell, which can be especially harmful to the brain.
An excessive water intake is anything over four litres a day, unless it’s extremely hot or you’re an athlete. Even so, athletes are at risk of over-drinking, especially if they try to rehydrate too quickly, resulting in what is known as water intoxication. Symptoms include blurred vision, nausea and vomiting. Scientists have discovered humans have a biological mechanism which makes swallowing harder when you’ve had enough liquid. So if you have to force water down, you’ve probably had enough.
Every drop counts
Drinking water is the most effective and affordable way to rehydrate, but all liquids count in the daily tally.
It’s a myth that tea and coffee don’t count. While these drinks may have a mild diuretic effect, causing you to produce more urine, you ultimately get more fluid than you lose. Still, excessive amounts of caffeinated drinks can cause headaches and insomnia, so it’s best to keep your levels of caffeine to less than 400mg a day, which equates to about four cups of brewed coffee, or 4–13 cups of tea.
Did you know?
- A slice of bread can be 40-50% water
- You can lose up to 1.5 litres of water during a three-hour flight
- Drinking salt water will make humans sick
- We lose half a cup of water each day just by breathing
- Fruit contains between 65% and 95% water
- We feel thirsty when our water levels drop by 1%
Article sources and references
- Australian Beverages. 2013. Caffeine — The facts. www.australianbeverages.org/for-consumers/caffeine-facts/ Accessed November 2015https://www.australianbeverages.org/initiatives-advocacy-information/
- Baylor College of Medicine. 2015. Thirsty? You’re already dehydrated; June 15, 2015. www.bcm.edu/news/sports-medicine/thirsty-you-are-already-dehydrated Accessed November 2015https://www.bcm.edu/news/sports-medicine/thirsty-you-are-already-dehydrated
- BBC Science. 2014. Maintaining water balance. Available at www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/homeostasis/waterbalrev1.shtml Accessed November 2015https://www.bbc.com/bitesize/guides/zp29y4j/revision/4
- Benton D et al. 2016. Minor degree of hypohydration adversely influences cognition. American Journal of Clinical Nutrition 1014:603-12https://www.ncbi.nlm.nih.gov/pubmed/27510536
- Better Health Channel. 2014. Kidneys. www.betterhealth.vic.gov.au/health/conditionsandtreatments/kidneys Accessed November 2015https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/kidneys
- Better Health Channel. 2015. Caffeine. www.betterhealth.vic.gov.au/health/healthyliving/caffeine Accessed November 2015https://www.betterhealth.vic.gov.au/health/healthyliving/caffeine
- Better Health Channel. 2015. Fatigue fighting tips. www.betterhealth.vic.gov.au/health/conditionsandtreatments/fatigue-fighting-tips Accessed November 2015https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/fatigue-fighting-tips
- Blue Planet. 2015. Water Facts. www.blueplanet.nsw.edu.au/water-facts/.aspx Accessed November 2015http://www.blueplanet.nsw.edu.au/water-facts/.aspx
- Cleveland Clinic. 2013. What the color of your urine says about you. www.health.clevelandclinic.org/2013/10/what-the-color-of-your-urine-says-about-you-infographic/ Accessed November 2015https://health.clevelandclinic.org/
- Migraine Research Foundation. 2015. About Migraine. www.migraineresearchfoundation.org/about-migraine.html Accessed November 2015https://migraineresearchfoundation.org/about-migraine/
- National Health and Medical Research Council (Australia) & Ministry of Health (New Zealand). 2006. Nutrient Reference Values for Australia and New Zealand Including Recommended Dietary Intakes. Canberra: NHMRChttps://www.nhmrc.gov.au/sites/default/files/images/nutrient-refererence-dietary-intakes.pdf
- NHS Choices. 2014. A small amount of coffee will not dehydrate you. www.nhs.uk/news/2014/01January/Pages/A-small-amount-of-coffee-will-not-dehydrate-you.aspx Accessed November 2015https://www.nhs.uk/news/food-and-diet/a-small-amount-of-coffee-will-not-dehydrate-you/
- The Pain Centre of Arizona. 2013. Is dehydration causing your headache? www.thepaincenter.com/news/headaches-and-dehydration Accessed November 2015https://www.thepaincenter.com/news/headaches-and-dehydration