Listen to your thirst - and drink water instead!

How much fluid should I drink to keep my kidneys healthy? 

The human body can last weeks without food, but only days without fluid.  It has no way to store the fluid it needs to replenish the blood in order for body functions to work properly, to make up for losses from lungs, skin, urine and faeces.  Fluid regulates the body’s temperature through perspiration, the kidney removes waste via urine, and carries nutrients and other substances throughout the body.  Fresh supplies of fluid are needed every day, however, there is no set amount to drink each day.  Drink to satisfy thirst is a good guide.

Kidney Health Australia Position Statement on drinking water - April 2003

The desirable amount of water to drink each day has been promoted to the public in recent years to be 8 glasses each of 8oz (= 240 ml) each 24-hour period. This view had in the past been publicised by water authorities and bottled water manufacturers, with endorsement of this view by Kidney Health Australia.

However, after our Kidney Health Australia medical team conducted a critical review of published literature in 2003, we found there is a distinct lack of evidence in published literature supporting this position.  As a result of this review our Board of Directors adopted the following position in regard to water intake.

There is a lack of evidence that drinking water in excess of thirst is beneficial for the health of Australians living in temperate regions and not exercising strenuously. To satisfy thirst,  water is the recommended fluid.  Drinks containing sugar or caffeine or alcohol all may cause or worsen health related problems and should be avoided except in modest quantities.

• The daily fluid intake needs are increased in:
  • All residents in tropical or hot climates
  • Individuals practising strenuous exercise
  • Certain medical conditions characterised by excess obligatory fluid loss
  • Certain medical conditions requiring an increased urine flow
    
• The daily fluid intake needs are decreased in most patients with
  • End stage kidney failure
  • Certain cardiac and respiratory conditions
    
• From the kidney viewpoint all fluids including those containing caffeine and alcohol should count towards the daily fluid total.

So what should you drink? 

If you’re thirsty, drink water instead.  Water is the recommended fluid to satisfy thirst and nature's choice.  It is calorie-free, inexpensive and readily available and choosing to drink water instead will have a positive impact on your health.  It can also contain fluoride which is good for the teeth.   

* View Kidney Health Australia's Position Statement on water fluoridation.  More>
** National Kidney Foundation (USA) have updated their Fluoride Position Statement for people with CKD.  More>

Note that commercially bottled mineral water contains salt which can lead to fluid retention and swelling and even increased blood pressure in susceptible people. Limit the amount of mineral water you drink or check the label and choose low sodium varieties (less than 30mg sodium per 100ml).

Other sources which hydrate the body

You don't need to rely only on what you drink to satisfy your fluid needs.  What you eat also provides a significant portion of your fluid needs.  On average food provides about 20 percent of total water intake, while the remaining 80 percent comes from water and beverages of all kinds.

For example, many fruits and vegetables — such as watermelon and cucumbers — are nearly 100 percent water by weight. Beverages such as milk and juice are also comprised mostly of water. Milk is important (especially for children) and tea can be a source of antioxidants, which appear to protect against heart disease and cancer.  Fresh fruit is preferable to fruit juice because it has more fibre and nutrients and less sugar.  Even beer, wine and caffeinated beverages such as coffee, tea or soft drink can contribute, but should not be a major portion of your daily total fluid intake. 

Sweet drinks should be limited as they add calories without nutrient value.  Caffeine or alcohol may cause or worsen health related problems and should be avoided except in modest quantities.  

Situations when you need to listen to your thirst 

Though no single formula fits everyone, knowing more about your body's need for fluids will help you estimate how much water to drink each day.  The amount of fluid you need to drink depends on your size, activity level and the weather. The best way of knowing how much to drink is to drink enough to satisfy your thirst. 

Other situations when you may need to ensure that you listen to your thirst are:

Exercise.  The more you exercise, the more fluid you'll need to keep your body hydrated. During long bouts of intense exercise, it's best to use a sports drink that contains sodium, as this will help replace sodium lost in sweat and reduce the chances of developing hyponatremia, which can be life-threatening. Fluid also should be replaced after exercise. 

Environment.  Hot or humid weather can make you sweat and requires additional intake of fluid. Heated indoor air also can cause your skin to lose moisture during wintertime.  Further, altitudes greater than 2,500 meters (8,200 feet) may trigger increased urination and more rapid breathing, which use up more of your fluid reserves. An air traveller can lose approximately 1.5 litres of water during a three-hour flight.

Illnesses or health conditions.  Signs of illnesses, such as fever, vomiting and diarrhea, cause your body to lose additional fluids and in these cases you should ensure that you keep your body hydrated.  Certain conditions including bladder infections or urinary tract or kidney stones, also require increased water intake.  On the other hand, certain conditions such as heart failure and some types of kidney, liver and adrenal diseases may impair excretion of water and even require that you limit your fluid intake.

 If you have severe kidney disease.  Your healthcare team will let you know if you need to limit fluids and how much fluid you can have each day. 

Pregnancy or breast-feeding.  Women who are expecting or breast-feeding need additional fluids to stay hydrated. Large amounts of fluid are lost especially when nursing.

Dehydration in elderly.  Insufficient signalling mechanisms in the elderly mean that they do not feel thirsty, even though they may be dehydrated.  Keep this in mind if you are caring for an elderly person as they may need prompting around fluid intake.  Some negative effects of dehydration in the elderly may include mental confusion, dry skin, migraines, hypertension, digestive complications and persistent constipation. Severe dehydration over time could even cause organ failure.  Elderly people are often at risk of dehyration due to:

• Changes to kidney function, which declines with age
• Hormonal changes
• Not feeling thirsty
• Medication (for example, diuretics and laxatives)
• Chronic illness
• Limited mobility

Dehydration in children.  Children are susceptible to dehydration, particularly if they are ill. Vomiting, fever and diarrhoea can quickly dehydrate a baby.  This can be a life-threatening condition.  If you suspect dehydration, take the child immediately to the nearest hospital emergency department.  Some of the symptoms of dehydration in a child include:

• Cold skin
• Lethargy
• Dry mouth
• Depressed fontanelle on the skull
• A blue tinge to the skin as the circulation slows

What is dehydration?

Dehydration occurs when the water content of the body is too low and is easily fixed by increasing your fluid intake. It is very important that you listen to your body' s signals that you are thirsty or have not had enough fluid intake.  Symptoms of dehydration include headaches, lethargy, mood changes and slow responses, dry nasal passages, dry or cracked lips, dark-coloured urine, weakness, tiredness, confusion and hallucinations. 

If you do not have enough fluids to keep your body hydrated, eventually urination stops and your kidneys will fail.  The body can’t remove toxic waste products and in extreme cases, this may result in death.

Dehydration - symptoms and what to do:

• Early dehydration dry mouth, thirst, restless or irritable behaviour, headache, mild muscle cramping.
• Moderate dehydration dry mouth, extreme thirst, flushed face, warm and dry skin, lack of urine production, dizziness, weakness, cramps in the arms and legs, headache.
• Severe dehydration all of the above, plus severe cramping, low blood pressure, fainting, convulsions, bloated stomach, lack of elasticity of the skin, rapid and deep breathing, fast and weak pulse – in extreme cases, heart failure.
• The treatment If you develop early signs of dehydration, get out of the sun; ideally go somewhere cool and in the shade. Splash yourself with tepid water or apply cool, wet cloths to your face and neck, and drink water slowly, small sips at a time. If your symptoms are not relieved within half an hour or so, or you go on to develop more severe symptoms, such as an inability to pass urine, vomiting, weakness or cramping, consult a doctor immediately.

Causes of dehydration include:

• Increased sweating due to hot weather, humidity, exercise or fever.
• Increased output of urine due to a hormone deficiency, diabetes, kidney disease or some medications.
• Diarrhoea or vomiting.
• Recovering from burns.

You may need more fluid in your diet if you are:

• On a high protein diet.
• On a high fibre diet, as fluids help prevent constipation.
• Have an illness that causes vomiting or diarrhoea.
• Are physically active.
• Are exposed to warm or hot conditions.

• Fluid loss needs to be replaced.
• Body fluid is higher in men than in women, and falls in both with age.  
• Fluid loss may be more in hot weather and with prolonged exercise.
• Most mature adults lose about 2.5 to 3 litres of fluid per day.
• Elderly people lose about 2 litres per day.
• An air traveller can lose approximately 1.5 litres of water during a three-hour flight.  

All living creatures needs clean and safe drinking water, but how much do you need?

Although Dr Goldfarb and Dr Negoianu wish they could demolish all of the urban myths found on the internet regarding the benefits of supplemental water ingestion, they do concede there is also no clear evidence of lack of benefit.  In fact, there is simply a lack of evidence in general.  

As a nephrologist, Dr Goldfarb is interested in how the kidney handles fluids, which prompted he and Dan Negoianu to review scientific literature on the benefits of drinking water.  Their conculsions debunk four myths. 

Myth No 1 - Drinking a lot of water suppresses appetite

Dr Goldfarb said, yet there is "no consistent evidence" that water suppresses appetite.  "Many people drink water before and during the meal to try to suppress their appetite," Goldfarb stated, yet there is "no consistent evidence" that water suppresses appetite.  "Because you absorb water so quickly and it moves through the GI tract so quickly, it probably doesn't fill you up the way people have proposed, nor does it lead to the release of hormones which suppress appetite as far as we know," Goldfarb affirmed.

However, they did suggest that the data regarding satiety and thermogenesis were intriguing, but insufficient to clarify the role of water intake in reducing the obesity epidemic.  There are multiple issues to test, but further research in this area could provide enlightening evidence which could change obesity-related outcomes such as caloric intake and body weight.

Myth No 2 - Drinking lots of water flushes toxins from the body and improves kidney function

No clinical evidence exists to back this up.  Goldfarb reported that this is not how the kidney works. "When you drink a lot of water you end up having a larger volume of urine but don't necessarily increase the excretion of various constituents of the urine.  Sodium and urea might be expelled, but there is nothing to back up any clinical benefit to this.  Some have even claimed that water intake can benefit the function of organs; however no studies have documented this type of benefit either."

Water ingestion can acutely affect GFR, although not necessarily in the direction one migh expect.  Evidence was found that increased water intake, actually decreases GFR.  A variety of studies reveal that drinking water does have an impact on clearance of various substances by the kidney, including sodium and urea. However, these studies do not indicate any sort of clinical benefit that might result.  It might therefore seem that any 'toxin' removed purely by glomerular filtration is cleared less efficiently in the setting of increased water intake, however, it is not certain such changes in GFR persist over time. 

Myth No 3 - Drinking water reduces headaches

It does not, according to the evidence.  Only one study could be found to back this up, and the results of the study lacked statistical significance.

Myth No 4 - Drinking water drinking improves your skin

No scientific data suggests that it actually improves the water content of the skin.  Although there is evidence that dehydration affects the skin, there are no data to suggest that it actually improves the content of the skin.

Dr Goldfarb and Dr Negoianu did find solid evidence that people living in hot, dry climates, as well as some athletes, have an increased need for water, and people with certain diseases like kidney stones may benefit from increased water intake - but no such data exist for average, healthy individuals.

There are circumstances where drinking a lot of water may be actually unhealthy

In long-distance runners more harm is done by long distance runners over-drinking during races than by long distance runners who under-drink.  Dr Goldfarb further cited a case of a woman who developed swelling of the brain and died when she drank water continuously and very rapidly for several minutes as part of a contest.