Water & Hydration

Water is a vital nutrient!

Water is essential to life given the role it plays in metabolism, transportation, circulation and temperature regulation (Horswill & Janas, 2011). The human body can last weeks without food, but only days without water.

Hydration has the largest beneficial effect on performance of any single nutrient (Zoorob et al, 2013)

Your body has no way to store water and it needs fresh supplies every day.  Each day humans must consume a certain amount of water to survive. The amount of water we need depends on your body size, your metabolism, your activity levels, the weather, and the food you eat.  If you are physically active or even training, you will need a high intake of water on a daily basis.

Generally, an adult male needs about 3 liters (3.2 quarts) of water per day while an adult female needs about 2.2 liters (2.3 quarts) of water per day. All the water a person needs does not have to come from drinking liquids, as some of this water is contained in the food we eat.

In adult men, about 60% of their bodies are water.  In adult women, 55% of their bodies are made of water. 

The unique qualities and properties of water are what make it so important and basic to life.  Water serves a number of essential functions to keep us all going.

• The cells in our body are full of water, which is a vital nutrient to the life of every cell. 
• Water forms the basis of blood, digestive juices, saliva, urine and perspiration, and is contained in lean muscle, fat, joints, and bones.  It is water that keeps the blood liquid enough to flow through blood vessels.
• Water regulates our internal body temperature through sweating and respiration: every time you exhale, you are exhaling water in your breath.
• The carbohydrates and proteins that our bodies use as food are metabolized and transported by water in the bloodstream; Water's "stickiness" (from its’ surface tension) plays a part in our body's ability to transport these materials all through ourselves.
• No less important is the ability of water to transport waste material out of our bodies in urine.
• The excellent ability of water to dissolve so many substances allows our cells to use valuable nutrients, minerals, and chemicals in biological processes.
• Water acts as a shock absorber for the brain, spinal cord, and organs in general.

The word hydration is verb, meaning to restore moisture.  When an individual has a normal body water content, they are euhydreated.  When they have a lower than normal content, they are hypohydrated.  The term dehydration refers to the process of losing body water, but it is often used incorrectly to describe hypodration, meaning their body water content is too low (Armstrong, 2007).

Hydration
Water is essential for the metabolism of some macronutrients, such as glycogen, which can only be stored in the muscle when bound to water in a ratio of 1:3 g (Murray & Rosenbloom, 2018). It is glycogen that provides energy for exercise, so maintaining daily adequate hydration is especially important for athletes.

However, it is important to maintain a balance, so as to not overhydrate and drink more than you need. This is referred to as hyponatremia, which is where the overhydration has created an electrolyte abnormality, reducing the body’s sodium concentration to less than 135mEq/L.  In this state, your body’s water levels rise and your cells begin to swell, and it can become life-threatening (Montain et al, 2006; Knechtle et al, 2019). 

It recommended to drink when you become thirsty.  It is not recommended to drink as much as possible before or during exercise.  It is most important to ensure that your fluids are replaced during recovery (Millard-Stafford et al, 2012).

          Tip:  You drink today for tomorrow – is the best advice.

Dehydration
Dehydration is not a disease, and it only has one symptom and that is thirst.  If you begin to exercise, after a period of time, you will become thirsty – that’s your body’s way of telling you to drink (Noakes, 2012)

Fluid balance is fundamental for athletes, as hypohydration, which occurs when body water levels are lower than normal due to excessive sweating during exercise or diarrhea, can have life-threatening consequences and negatively impact performance (Barley et al, 2020).

Athletes should be aware that the body can lose fluids in typically two ways: through sweating as a natural result of prolonged exercise and through urination.  The degree of each is driven by exercise load, and other factors such as temperature and humidity (Periard, et al, 2021)

Furthermore, fatigue, injury, immunosuppression, and decreased performance can occur not only when energy expenditure regularly exceeds daily caloric intake but also when hydration is insufficient (Jones et al, 2008; Casa, 1999; Cade et al, 1999; Murray & Rosenbloom, 2018).

Thirst is often not an effective indicator of dehydration, as 1.5 liters can be lost before thirst perception (Consensus Statement, 2012). Athletes are susceptible to losing 0.3 to 2.4 L per hour of sweat, which includes not only water but also salt, potassium, calcium, magnesium, and chloride.

Hydration and Recovery
It is crucial to replenish fluid loss after exercise. Researchers have found that losing 2% of body fluids can affect performance and cognitive function.

One of the first goals during recovery is to replace any fluid and electrolyte deficits. Most physically active individuals sweat from 0.3 to 2.4 L·h⁻¹, which would be contingent on the intensity of exercise, duration, and environmental conditions such as altitude, heat, and humidity (Thomas et al, 2016). Moreover, individual characteristics (i.e., body mass, genetic predisposition, heat acclimatization state, physical fitness, and metabolic efficiency) might influence sweat rates for a given activity (Sawka, 2007)]. For instance, the highest sweat rate was registered at 3.7 L·h⁻¹ for a world-class ultramarathon runner (Kreider, 1991). Thus, measuring pre- and post-exercise body mass is a recommended practice to assess fluid status.

Rehydration is a fundamental step in recovery, but what, how, when and how much will depend on the athlete and the particular event. All athletes should be educated on personal sweat rates, hydration cues, and rehydration strategies that avoid both hypohydration and fluid overload (Roberts et al, 2017). Replacing fluids lost through sweat is top priority for recovery. A total of 16 to 24 oz of fluid should be consumed for every 1 lb lost (Cade et al, 1971).

Athletes and practitioners should replenish three cups of fluid per pound of weight lost (~1.5 L·kg⁻¹) and to make sure body mass is back up before the next training session.

Rehydration can take between four and 24 hours (Burke, 2010).

In the case of half, full, and double marathons, like the Comrades, be cognizant of your fluid intake as too much is not good either.

Bottom line – water is your best fluid to sustain your performance and if competing it is best ingested the days before your event, then replaced during recovery.

References

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