Heather Bedard, C.H.E.
While we all learned in school that water is important to drink, many people do not drink enough water because they don't feel thirsty, don't like the taste, or they prefer other beverages such as coffee, tea, or sports drinks. Let's dive in to what water does for us and why it's important.
The human body, as an infant, consists of 75% water and we gradually lose that percentage as we age. In old age the percentage is lowered to about 55%. This is potentially because aging results in lowered thirst sensation and many elderly people do not drink as much water as younger people. Research supports this as shown in a study dehydration in elderly people.(1)
The human body typically loses about 10 cups of water a day through sweating, breathing, talking, and stool. People eating a whole food diet, rich in plant foods – which contain a good amount of water – can ingest about 2 cups of water in this way. That leaves about 8 cups of water to consume on average. If you are physically active to where you are sweating more, or in the heat, you will need to consume more. (2) For kids this number typically comes out to ½ of their weight in ounces.
Water balance is controlled very tightly in the body. When you become dehydrated, meaning you haven’t consumed enough water, water is moved from inside the cells to extracellular areas. This loss of water causes the cells to shrink. The cells shrinking leads to a series of events including signaling the body to drink and informs the kidneys to concentrate waste in less amounts of urine. This happening once in a while isn’t a big issue, but if it happens consistently over time can result in wear and tear on your kidneys. This is especially true if you are consuming a lot of toxins that are being eliminated in the smaller amount of urine. One of the best ways to protect your kidneys is to drink enough water!
Really quickly, on this point about the kidneys, many people unknowingly stress their kidneys through chronic dehydration AND consuming diuretics such as alcohol. When you drink alcohol, it inhibits the pituitary gland from releasing a hormone called anti-duretic hormone. This hormone typically signals to the kidney to reabsorb water and retain salt when someone is dehydrated. When this hormone is blocked, it means that your kidneys, which are working to remove the alcohol from the blood stream, are sending more water to your urine. Exactly how much extra urine is produced from a glass of wine is still up for discussion, but most agree its at least one glass of wine worth for the first drink. As you can see, this can easily lead to even more dehydration.
Ok, so let’s get back to what happens in the body when you’re dehydrated. As I mentioned before, when your cells shrink, it signals to your body that you are thirsty. Secondly, it results in a craving for salt. This is because sodium, along with potassium, regulates water levels in your body! Both of these minerals are also known famously as electrolytes. When the cells lose their balance of these electrolytes in the cells it causes a chain reaction. This is why it’s important if you are exercising and losing a lot of water through sweat,s or even just outdoors on a hot day, to be sure you are drinking enough water and consuming enough electrolytes. No, this doesn’t mean a chemical and sugar laden sports drink. But you can do this by eating whole foods like spinach, banana, and sunflower seeds, making your own electrolyte drink, or drinking good quality water that hasn’t had the minerals filtered out. But I would just encourage you to pay attention to your body when you are having cravings for liquids or salty foods and maybe try to fill that craving with water instead of other beverages.
When you are dehydrated you may feel hotter than usual. This is because the core temperature of your body is increased. As you may remember from school, sweating and evaporation of sweat is how you cool yourself. So, when you’re exercising hard or outside on a hot day, you are losing water and disrupting that electrolyte balance. Typically, this is not difficult to restore. However, if you do not replace the water and electrolytes you have lost from sweating bad things happen!
The first thing is that your sweat production is lowered which in turn means that your body is not able to cool itself. Therefore, your internal temperature increases. This isn’t the only downside. Other functions in the body that rely on water are also affected. Plasma is the part of your blood that carries water, salts, and enzymes. It makes up about 55% of your blood content. About 92% of that is composed of water. That means, when you are dehydrated, plasma volume is reduced and blood viscosity, or thickness is increased. That in turn reduces cardiac output and then because your body is stressed, cortisol is produced. This experience can often be more pronounced in children. (3)
When you are dehydrated, it often presents with a headache. This is due to dehydration of the brain and reduced blood plasma volume. Drinking water could provide pain relief in a short amount of time…even 3-mins to 3 hours for even migraine headaches due to dehydration. (4)
You may be thinking, "Well I don’t drink a lot of water and I don’t feel dehydrated." Studies show that thirst is not always an accurate indicator of hydration level, and this can result in chronic dehydration. This is of note when it comes to working out. Many people work out in a dehydrated state which results in reduced blood flow to the muscles and the effects that I described above. (5) This occurs even when those who are exercising do not feel thirsty. (6) In other words, you cannot rely on thirst alone to tell you that you need to drink water. A better option would be to make sure that you are drinking at least 8 cups of water a day and closer to 10 if you are really sweating and exerting yourself. Most people are working out to improve their physical stamina and challenge their bodies. If you are not adequately hydrated, you will have reduced endurance, more fatigue, and less return on your output. This is shown in a study on the influence of graded dehydration on hyperthermia and cardiovascular drift during exercise. (7)
It really doesn’t take much to feel the effects of dehydration on your system as a study on hydration and physical performance found. (8) More research needs to be done but you are better off being hydrated than not!
Some health professionals recommend urinalysis to determine hydration levels but urinalysis really only tells you measures recent fluid intake and not your overall hydration status.
When all is said and done, caring for your body with proper hydration is one of the simplest, and easiest, things you can do for your health.
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Phillips P, Johnston C, Gray L. “Disturbed fluid and electrolyte homeostasis following dehydration in elderly people.” Age Ageing 1993 Jan;22(1):S26-33.
Jequier E, Constnat F. “Water as an essential nutrient: the physiological basis of hydration.” Eur J Clin Nutr 2010 Feb;64)(:115-123)
Bytomski J, Squire D. “Heat illness in children.” Curr Sports Med Rep 2003 Dec;2(6):320-4.
Blau J, Kell C, Sperling J. “Water-deprivation headache: a new headache with two variants.” Headache 2004 Jan;44(1):79-83
Maughan R, Watson P, Shirreffs S. “Heat and cold: what does the environment do to the marathon runner?” Sports Med 2007;37(4-5):396-9.
Bar-Or O, Dotan R, Inbar O, Rotshein A, Zonder H. “Voluntary hypohydration in 10-to 12-year-old boys.” J Applied Physiol 1980 Jan;48(1):104-8.
Montain S, Coyle E. “Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise.” J Appl Physiol 1992 Oct;73(4):1340-50.
Murray B. “Hydration and physical performance.” J Am Coll Cutr 2007 Oct;26(5 Suppl):542S-548S.