The importance of hydration

5 min read – fact checked ✔

Why hydrate?
Water is essential for life, the major component of body fluids and plays a critical role in many other biological processes, including helping to regulate body temperature through sweating. Fluid balance in the body is carefully controlled by varying the concentration of fluids in the blood and urine, resulting in the release of a variety of hormones which trigger either satiation or thirst. Body loses of water occur in urine and faeces as well as smaller amounts through the skin, lungs, digestive enzymes and lacrimal glands on a daily basis. If sufficient fluids are not consumed to replace those which are lost, then the body enters a state of dehydration. Mild dehydration may result in approximately 1-2% loss in bodyweight lost, and may lead to headaches, tiredness, lack of concentration and may even affect athletic performance ⁽¹⁾. Fluid requirements vary between individuals and depend on a variety of factors such as age, level of activity, and climate. UK Government advice on fluid intake recommends consuming 6-8 glasses per day, which equates to around 1.2 litres in total; 6 x 200ml glasses or 8 x 150ml glasses ⁽²⁾. However, many may not be aware that water is also found in a large number of delicious fruits and vegetables which can not only hydrate you, but also contribute to your five-a-day. Scroll to the end of the page to view the list and become hydration saavy, or carry on reading to understand some more about the science of water and the human body.

CLICK TO EXPAND AND LEARN MORE ABOUT THE IMPORTANCE OF WATER TO HUMAN PHYSIOLOGY

Biological actions of water
Water is an inorganic, transparent, tasteless, odorless, and virtually colorless chemical substance, and the main constituent of earth’s hydrosphere and the fluids of all known living organisms. Although humans can survive for several weeks without food, they cannot normally go without fluids for more than a just a few days. On average, water makes up around 60% of body weight in males and about 50-55% for females, although this varies depending on age and body composition as a higher percentage of body fat equates to a lower proportion of the body water. Water is essential for the function of all the cells in the body and a major constituent of body fluids (such as lymph, saliva, bile) and has many other biological roles ⁽³⁾:-

• Acts as a lubricant for the joints and eyes
• Medium where most reactions occur in the body
• Acts as a cushion for the nervous system
• Helps transport nutrients and elimination of waste via faeces, urine and plasma
• Helps to regulate body temperature

How hydration status is maintained
The body has sensitive mechanisms to maintain hydration status and to prompt drinking but young children and older or ill adults may need support to maintain adequate hydration.. Fluid intake is important to maintain hydration when physically active and is advised before, during and after activity. If active at higher levels for long periods (such as intense activity lasting more than 1 hour), drinks with added carbohydrate and electrolytes may be advisable to rehydrate more quickly and replace electrolytes lost in sweat. Total water losses from skin may range from as little as about 100 mL (up to about 300 mL insensible only) to well over 1 L (with extensive sweating). The kidneys play a critical role in fluid regulation in the body under the influence of several hormones including vasopressin, the renin- angiotensin-aldosterone system, and natriuretic peptides influencing renal function, the cardiovascular system, among others, to correct imbalances in the body’s fluid and sodium levels, as well as other major minerals ⁽⁵⁾. These fine fluid / electrolyte balances are required to maintain hydrostatic pressure which is the water movement between the interstitial fluid and the plasma, colloidal osmatic pressure which is the water movement across the capillary walls (the endothelium) that separates the plasma and the interstitial fluid, and finally osmolarity, which helps maintain extracellular volume to control blood pressure and cardiovascular function.

What are good sources of hdyration?
We can get fluids from foods and drinks as depicted in the image below, although young children and older or ill adults may need support to maintain adequate hydration ⁽²⁾. Water can also be obtained from drinks such as squash, fruit juice, soft drinks, milk, tea and coffee. However, not all sources are ideal. For example, although some forms of alcoholic beverages (ie red wine) may confer some degree of benefit to some individuals, the effects according to the research appear to be genetic, dose and frequency-dependant, which may explain the great deal of discrepancy in the literature ⁽⁷⁾. Alcohol is also a diuretic and potentially poses risk to human health such as weight gain and liver disorders, and therefore, alcoholic drinks should not be considered as contributing to fluid intake ⁽⁷⁾. Other beverages are high in added sugars, so caution is warranted when consuming drinks such as some commercial fruit juices and speciality drinks. Excessive sugar intakes can also have a considerable negative effect on fluid balance and blood pressure ⁽⁹⁾. Caffeine has a diuretic effect that may influence the net retention of ingested water ⁽⁸⁾. Therefore, comparing water content of foods without considering the presence of the other substances that may impact ingested water availability does not provide accurate picture of a particular food or the beverage’s hydration value. In a practical sense, it may be better to choose foods that contain both high water content and provide other ingredients that can facilitate the hydration process as well as provide a wider range of other important nutrients which can positively influence wellbeing, such as those suggested at the end of this article – stay with me read on.

Other factors affecting hydration
Heat, humidity and physical activity can increase fluid and electrolyte requirements ⁽¹⁾ and more fluids may be needed to maintain hydration. Sports drinks with added carbohydrates and sodium are usually not needed when taking part in moderate activities, but when engaged in intensive exercises for longer than an hour, commercial or home-made sports drinks may help to rehydrate more quickly, provide energy, replace sodium losses and balance electrolytes.

Could you be over hydrating?
Although dehydration can impair cognitive and physical performance in mild cases, and in extreme cases can be fatal, it can also be dangerous to drink excessive amounts of water in combination with a low salt intake or sodium losses occuring via excessive sweating in warm climates and/or physical activity ⁽¹⁾ and could result in rare cases of water intoxication (hypotonic overhydration). Over hydration could lead to hyponatraemia (low levels of sodium in the blood), causing the inside of your cells to contain too much water and thus swell due to an abnormal sodium level in your bloodstream, often when sodium level reaches dangerously low levels with concomitant excessive water consumption. Water intoxication is more serious than you think, and could progress to a point that causes major health problems. These include falling into a coma, seizures and can even result in death ⁽⁵⁾.

The importance of salt and individual needs.
Although UK dietary guidelines recommend daily reductions in salt intakes, not everyone is salt-sensitive, as studies have shown that the links between salt intake and health outcomes may have a large variety of determinants, including genetic factors, race/ethnicity, age, body mass, overall diet quality including macro- and micronutrient content, as well as associated underlying disease states, e.g. hypertension, diabetes and renal dysfunction ⁽¹⁶⁾. Thus not everyone may be affected by responsible salt intakes in the same way especially when most salt-containing processed foods are removed, evidencing the need for individual assessment and personalised nutrition ⁽¹⁶⁾. I could help you determine your salt tolerance and metabolic function via blood and genetic assays – contact me for more info and lab testing. Therefore, balancing water intake with sufficient sodium is critical for proper fluid balance, muscle and nerve function.

Be hydration savvy
Many fruits and vegetables contain very high levels of water as a percentage of weight ⁽¹⁵⁾ and thus contribute to your daily fluid intake (see tables below), with the added benefit of providing a whole host of other important nutrients such as fibre, vitamins, minerals and antioxidants which could positively affect your physiology apart from helping to maintain proper fluid / electrolyte balance. Increasing consumption of a combined minimum five-a-day 80 gram portions of fruit and vegetables as recommended by the UK Government dietary guidelines ⁽¹⁰⁾ could help to optimise health ⁽¹¹⁾. 80 grams is approximately equivalent to your closed fist or a small apple. Antioxidants may help quench free radicals produced from daily metabolic processes, inflammation, daily stressors and environmental toxins which can negatively affect health ⁽¹²⁾. The increase in 5-a-day fruit and veg intake may also help you achieve the UK daily recommended minimum fibre targets of approximately 30 grams a day ⁽¹³⁾, which could help improve digestive function and systemic health ⁽¹⁴⁾. Therefore, the next time you are feeling thirsty and feel the need to hdyrate, opt for a fresh fruit or veggie instead, you may thank me later!

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