The typical human body’s mass is made up of about 60% water. It’s a bit lower in older people and females and higher in young children. Almost 99% of the molecules in your body are water. So, it is it is vital to make sure you get adequate hydration. But what does this mean?
Water is the primary building block of cells. It also carries essential oxygen and nutrients to the cells.
Water is needed for the body to use proteins and carbohydrates as food. It is also the main component in saliva which is used to digest carbohydrates, as well as actually swallowing the food.
Water acts as an insulator to protect the body’s temperature. It is also essential to cooling the body through perspiration and respiration. It is particularly important in insulating the brain, spinal cord, organs, and the foetus during pregnancy.
Water acts as a shock absorber in the body for both hard and soft organs. It also lubricates joints enabling basic movements.
Water is the principal solvent in the body. It dissolves minerals, soluble vitamins, and nutrients making them available to the body where they are needed. It is then used to flush waste and toxins from the body.
Loss of hydration will interfere with these processes. This can begin to happen fairly quickly and without you really noticing it.
A person will typically start to feel thirsty if they lose 2 to 3% of their body’s water. However, the impact of dehydration will be seen before that point. Mental performance and physical coordination will typically deteriorate at around 1% dehydration. Mood will also be soon affected.
And you don’t actually need to be doing much to deplete the water in your body by 1%. Just by breathing it will soon happen.
Given that getting adequate hydration simply means ensuring that you drink enough water, it would appear to be a relatively easy thing to achieve. However, it turns out that answering the question of what constitutes adequate hydration is not so simple.
What Does Adequate Hydration Mean?
There seems to be something of a consensus that drinking little and often is the best way to stay hydrated. For a typical person going about their business without engaging in strenuous exercise, typical recommendations for water consumption are in the range of 1.5 to 2 litres per day. Some of this intake will arise in the form of food which generally accounts for about 20% of water intake.
The correct intake may be as high as 2.5 litres for men with larger body sizes, but the recommendation of 2 litres a day for adults is widespread.
Some recommend more. According to the Mayo Clinic, citing research by the National Academies of Sciences, Engineering, and Medicine in the US, a man requires 3.7 litres of fluids per day while a woman requires 2.7 litres. These amounts include all intakes including water is solid foods.
Not everyone agrees, and it is claimed that there is little in the way of scientific evidence to support this recommendation. A good benchmark may well be the recommendation by the UK’s NHS to drink 6 to 8 glasses of water per day – about 1.2 litres – to prevent the onset of dehydration.
However, what you do during the day is a key factor in what intake is appropriate for adequate hydration. This will change depending on how much exercise you take, the weather and altitude, your overall health and during pregnancy and breast feeding.
Hydration and Exercise
The amount of exercise you take is a key factor in how much water you need to drink to ensure adequate hydration.
Water is critical to maintain blood volume, body temperature and muscle contraction when exercising.
Water loss can rise quickly as a result of sweating as the body aims to maintain core temperature while exercising. This loss of fluid will result in dehydration if fluid intake is inadequate.
When exercising for a defined period your body will be able to tolerate low to moderate levels of dehydration. As a result, you will not experience much in way of symptoms. However, if the level of dehydration rises your performance will be impaired. You will typically experience an increased heart rate for any level of exercise and an increased perception of the required level of effort.
Dehydration will lead to a more rapid onset of fatigue and more intense tiredness. It will then take much longer to recover.
You will experience reduced levels of skill and coordination and an overall loss of cognitive ability. This will persist after the exercise has finished, for example, when you are driving home afterwards.
If the dehydration is not addressed you will experience gastrointestinal issues, such as nausea. In extreme dehydration there is an increased risk of heat illness.
It’s a pretty ugly list. And it’s the same even if you are an experienced or fit athlete. But it’s fairly straightforward to avoid getting into this situation.
How much Hydration is Enough when Exercising?
You may wish to contact a sports dietitian to develop an individual hydration plan. However, there is a lot you can do by yourself.
Hydration needs are depend on the individual due to variations in sweat rates between people. These can also vary for the same person exercising in different conditions.
Always ensure you are well hydrated before you begin to exercise. Don’t overdo it. There is no benefit to performance beyond what is adequate and there can be detrimental impacts.
Being too aggressive with your hydration can lead to interrupted sleep the night before, bloating and gastrointestinal upset. It will also lead to the frequent need to urinate during the period of exercise.
Follow a hydration plan based on your individual needs while exercising. This can be quite simple and even a few repetitions of an exercise programme will soon indicate where you need more water and when you have enough.
Again, don’t overdo it. Excessive intake can result in hyponatremia where sodium levels in the blood become too dilute. However, this is usually only seen in endurance events, such as a marathon, if participants consume large volumes of low electrolyte fluids in excess of their needs.
Continue to rehydrate after you finish exercising. It’s not that your body continues to lose fluid at as high a rate as when exercising. However, it is unlikely that you will have drank enough while exercising to replace 100% of the fluids lost.
In fact, it is not necessary for adequate hydration that you will have done so and a good exercise regime will involve a temporary drop in hydration levels.
Keep in mind that there is no performance advantage to starting an exercise session over-hydrated and it is actually more likely to result in negative side effects.
A Lot depends on Your Individual Characteristics.
Your sweat rate is an important determinant of your hydration needs. This is influenced by factors including:
- Your body size. People with larger body sizes tend to sweat more.
- Your fitness level. Fitter athletes generally start to sweat earlier.
- The makeup of your genetics. Some people naturally sweat more than others.
- The ambient temperature. Hot and humid conditions increase sweat rates.
- Whether there is adequate air flow. Air flow over the skin improves body cooling and reduces sweat rates
- The intensity of the exercise being undertaken. As intensity increases, so does sweat rate.
So, there is no ‘one size fits all’ approach that tells you how much to drink to replace the fluid you will lose from sweat. The important requirement is to be aware of your own hydration needs before, during, and after exercise.
Keeping that in mind, here is a simple online calculator that will provide you with an indication of the amount of water that you will require to replace fluids lost during exercise. It does attempt to take a range of factors into account, but it is a guideline and should not be used to supplant professional advice.
When it comes to ensuring adequate hydration, whether or not you are engaging in exercise, the best guide is self-monitoring. Do this during the course of the day and before, during and after exercise.
Ensure that you take in enough that you do not feel thirsty, you mouth is not dry, and your urine is regular and light coloured. Any deviation from this is a sign you need to act and increase intake.