Hydration – what it is and why it’s crucial
The importance of hydration lies in its role in allowing the body to perform our internal processes effectively and efficiently. Water is involved in a number of essential functions in the body. For example, it helps maintain our body temperature and acts as a primary material for our cells (the building blocks of our bodies). This means that staying hydrated is essential for our bodies to do their job to ensure that we can keep ourselves going. (1)
The function of water in the human body
As mentioned, water plays an important role in the body. It maintains our body temperature, helps transport signals to our brain, flushes out waste and helps deliver vital oxygen around the body. This, along with many other actions, is why water plays such a big part in our everyday lives.
Up to 60% of the human body is composed of water. This water is shared between our different organs (most organs contain up to 70% water). The brain and kidneys contain the highest percentage of water compared to other organs within the body. By ensuring that we are hydrated we can assist with the function of these vital organs. (2)
The composition of water in our bodies changes with age. Research shows that the bodies of older people consist of approximately 55% water, whereas the water composition of infants lies at about 75%. (3) As we age, the decrease in fluid composition of our bodies can cause issues such as urinary tract infections and constipation. Older people may be less aware that they aren’t getting enough fluids, and this can exacerbate issues with hypohydration, which we will explain in the following section.
Dehydration vs. Hypohydration
Simply put, dehydration is the process of losing water, whilst hypohydration is the end result, when we are in a water deficit. (4) This means that our bodies are losing more fluids than we are taking in. The signs of hypohydration are more noticeable than the signs of other nutrient deficiencies. Hypohydration is the uncompensated loss of water from our bodies, and this is when we begin to notice signs that we need to replenish our fluids by drinking liquids. For example, many of us have noticed a dry mouth, the feeling of thirst, the change in the colour of urine. These are signs of hypohydration and these are clear signals our body is giving us to rehydrate ourselves. We should listen to these messages carefully.
Hypohydration’s impact on focus, mood, and memory
Even mildly hypohydrated individuals (1-2% fluid loss) have shown impairments in cognitive performance. This means not being fully hydrated can affect our short-term memory, ability to focus on tasks, or our mood. (5) For example, a study conducted in school-age children found that children with better habitual hydration showed better cognitive flexibility than children who were less hydrated and providing a water intervention led to improved task-switching capabilities. (6)(7)
Hydration and our bowels
Our Hydration status can also impact our bowel movements. When we have bowel issues such as diarrhoea, this can cause our body to lose water via loose stools. Patients that suffer from chronic diarrhoea can also lose important electrolytes in the process. When we are re-hydrating post diarrhoea, we also have to consider the electrolytes that have been lost. The WHO have created an Oral rehydration formula containing different substances such as glucose and sodium to help with this. This is often used when children have diarrhoea. When we lose water, it is important that we replenish both the water and the electrolytes that were lost. (8)
How the body hydrates itself
The body always wants to be a constant state of physiological balance. This is known as homeostasis. When the body senses that the fluid balance is off, a deficit for example, it moves water stored on our cells outside of the cells to regain an equilibrium. Similarly, if the body feels that it is overhydrated, the opposite occurs and the kidneys help excrete the excess water. The kidneys play an important role in maintaining the fluid balance of the body by producing concentrated urine when we are dehydrated to conserve water (that is why we have dark urine when we are dehydrated). The body also tries to re-hydrate itself by sending signals to the brain to indicate that we feel thirsty.
How hydration changes as we age
Dehydration is the most common fluid complication amongst the elderly. This is a result of a diminished thirst sensation, decreased muscle mass (therefore giving a decreased body fluid composition), and older adults have less of an ability to produce more concentrated urine to preserve low fluid levels in the body. Along with have a reduced thirst sensation some older people have trouble swallowing, therefore thicker fluids may be required to hydrate themselves. Many older adults with swallowing issues do not enjoy the texture of thickened liquids and this could contribute to a reduction in fluid consumption for these groups. (9-11)
Role of the electrolyte in hydration
Electrolytes are substances that break down into positive or negative charges when dissolved in water. Some examples of electrolytes include sodium, potassium and chloride. These electrolytes work together to create channels of communication within our bodies to conduct actions such as nerve impulses and muscle contraction. (12)(13)
Electrolytes also play an important role in hydration. Electrolytes can be found in foods that we eat, so our nutrition can play a role in our hydration status as well! The kidneys help regulate the amount of electrolytes present in the body so that we don’t have too much or too little of them in our system.
As mentioned before, electrolytes carry charges. Sodium and potassium have a positive charge whilst chloride has a negative charge. Sodium and chloride are found in the fluid outside of our cells and potassium is found in the fluid within our cells. Chloride works hand in hand with sodium to transport substances in and out of cells. As sodium is positive and chloride is negative, the charges cancel each other out to ensure that a neutral charge is maintained, this is known as charge neutrality. (14)
Both Sodium and chloride can often be found in savoury foods containing salt. The chemical name for salt is sodium chloride. Sodium and chloride help to maintain the fluid outside of our cells. Often excess salt consumption is discouraged as it plays a role in high blood pressure, but sodium and chloride play crucial roles in fluid balance. This is because the regulation of salt and water balance in the body is highly inter-connected. Water is known to follow salt; this can contribute to the regulation of blood pressure and thus fluid balance. (15)
Another nutrient that plays a role in fluid balance is potassium. Potassium is often found in fruits and leafy green vegetables. It maintains the fluid inside the cells. Potassium and sodium work together to help us transport fluid where it is needed the most. (16)
Good beverages to help us hydrate
Instantly when we think of beverages to help us hydrate, we think of water. We are encouraged to take approximately 6-8 glasses of water per day to maintain good hydration. Water is a solid choice to maintain hydration, but we should also remember that all beverage consumption can contribute to good hydration. We should avoid sugar sweetened beverages to hydrate ourselves as they can help us hydrate, but over consumption of beverages such as these could put us at risk of issues with our dentition. Teas and coffees can also help with hydration. Although previously thought to exacerbate dehydration because of the diuretic effect of caffeine, these alternative options have been shown to ultimately push us toward a more hydrated state. (17) Fortified milk can be useful as a hydrating solution as it contains vitamins and minerals such as Vitamin D and calcium.
Hydration and activity
Also, to note that depending on the activity, you may need to consume more or less fluid, this can be dependent on timings for breaks for example. Those that play soccer or rugby might have a higher risk of hypohydration as the alternate pauses can sometimes interfere with our opportunity to rehydrate.
If we are expected to sweat a lot during activity, sports drinks may be a more suitable choice to rehydrate as the electrolytes within them can help the body retain fluid and give us energy. Post activity, milk can also be a good rehydration choice as along with the hydration properties, the protein found in milk can contribute to building and retaining muscle. It is always important to continue to rehydrate yourself when carrying out physical activity. (18)
Staying hydrated is very important for our overall health and well-being. We need water to survive, it is one of the primary nutrients required to sustain us. Hydration is key to maintain all of the bodies process and we must not take it for granted.
Hilary McCahill, BSc, RD
Hilary McCahill is a qualified dietitian in both Ireland and the UK and is a graduate of the human nutrition and dietetics programme jointly shared by Trinity College Dublin and Technological University Dublin. She is currently a quality graduate within Kerry Group’s graduate programme. She is passionate about all things food, health and nutrition having spent time working in both food industry and within clinical settings.
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- Masento, N.A., Golightly, M., Field, D.T., Butler, L.T. and van Reekum, C.M. (2014). Effects of hydration status on cognitive performance and mood. British Journal of Nutrition, 111(10), pp.1841–1852. doi:10.1017/s0007114513004455.
- Khan, N., Westfall, D., Jones, A., Sinn, M., Bottin, J., Perrier, E. and Hillman, C. (2019). The Effect of Hydration on Cognition in Children: The WITiKids Randomized Controlled Crossover Trial (OR32-08-19). Current Developments in Nutrition, 3(Supplement_1). doi:10.1093/cdn/nzz052.or32-08-19.
- NHS Inform (2019). Hydration | NHS inform. Nhsinform.scot. Available at: https://www.nhsinform.scot/campaigns/hydration
- Bennett, J.E., Dolin, R. and Blaser, M.J. (2019). Mandell, Douglas, and Bennett’s principles and practice of infectious diseases. Philadelphia, Pa: Elsevier.
- Białecka-Dębek, A. and Pietruszka, B. (2018). The association between hydration status and cognitive function among free-living elderly volunteers. Aging Clinical and Experimental Research. doi:10.1007/s40520-018-1019-5.
- Bruno, C., Collier, A., Holyday, M. and Lambert, K. (2021). Interventions to Improve Hydration in Older Adults: A Systematic Review and Meta-Analysis. Nutrients, 13(10), p.3640. doi:10.3390/nu13103640.
- Kerry Health And Nutrition Institute. (2017). The Retiring Nature of Taste Perception. Available at: https://khni.kerry.com/news/blog/the-retiring-nature-of-taste-perception
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