Water is one of life’s necessities, but it’s also one of those nutrients that seem to be always praised for wide-ranging benefits — anything from helping us think better to making skin look more youthful. The human body needs water to function properly, and as we can only live 2–3 days without hydration, it seems logical that we would need to drink copious amounts to stay healthy and keep our fluid intake and output equal. So, we do; anyone can tell you we need to drink 8–10 cups of water a day, and the sight of people toting around large water bottles and gulping down the required amount is long familiar. But is it necessary to drink that much throughout the day? Can it really help improve memory, prevent wrinkles, and assist with removing toxins from the body?
There is no evidence that healthy adults need to drink eight cups of water a day. Most adults achieve fluid balance just by following their thirst. And while there is a general recommendation for fluid intake (11–12 cups for women and men respectively), these are met through eating, drinking and even digestion. Food ranges in fluid content from 40 to 90 percent of weight, which provides two to four cups per day. All the fluid we drink (even caffeine-containing drinks like coffee and tea, as well as soup, juice, etc.) adds up to about six cups per day. And metabolism produces about one cup per day of water as a by-product. This adds up to about 9–12 cups of fluid! And we lose about that much from breathing, sweating and waste. So right there is fluid balance.
Many people are concerned about becoming dehydrated. Familiar with the statement that “thirst is the first sign of dehydration,” they continuously drink to prevent becoming thirsty. While dehydration is a serious concern (severe dehydration can put the body into shock or unconsciousness), thirst is merely a sign that the body needs fluid. Consider this comparison: “Hunger is the first sign of starvation” is an extreme exaggeration, and would require one to eat constantly to prevent any sign or feeling of hunger. Just as we can trust our hunger cues to inform us when to eat, we can trust our thirst cues to let us know when it’s time to drink, and how much.
Is water the cure for aging skin? Not likely. But for those who don’t have much fluid in their diet, it does appear that drinking more water (to reach 2000 mL [8 cups] of water/day) can improve skin physiology by making it more elastic and able to return to its original state after stretching. So, proper hydration may be beneficial for those with chronically dry skin.
Hydration status has a definite effect on the mind and body, as even mild dehydration increases fatigue, decreases alertness and affects mood, especially for those with poor thirst responses (including elderly people and children). Children clearly benefit from drinking more, with improved memory and cognition, and may need to be encouraged to recognize their thirst, or drink more frequently. While water doesn’t seem to improve memory for most people, when severely dehydrated, returning to adequate hydration can improve short-term memory and cognitive performance.
Toxins are removed from the body via the kidneys, lungs and skin. While water helps with movement through the body, more water will not remove more toxins, or even expedite the process. With increased water consumption comes increased water removal; the kidneys regulate blood concentration of minerals and electrolytes so tightly that excess water will be removed so as not to dilute the proper concentration, and ensure everything is at the proper level. An example of when this doesn’t happen is “hyponatremia” — low blood sodium, often caused by too much water in the body, which can cause edema, severe neurological impairments, seizures and death. While fluid assists with balancing these electrolytes and minerals, more is not better, as it will just leave the body.
Eight cups of water throughout the eight-hour day, or “8×8,” is an arbitrary recommendation that’s become popular and seems like the basis for a healthy lifestyle. While water is a necessary part of our daily intake, excessive amounts can cause harm. Fluid needs can change, depending on activity level, the weather, when ill, expecting or nursing, so it’s important to listen to your body’s needs and respect your thirst.
- Valtin, H. (2002). “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8×8”? Regulatory, Integrative and Comparative American Journal of Physiology 283 (5) R993–1004
2. N.A. (2004). Dietary references intakes: Water, potassium, sodium, chloride, and sulfate. Accessed from The National Academies of Sciences Engineering Medicine
3. Cook, D. (2017). 8 glasses of water a day is the mother of all hydration myths. Accessed from huffingtonpost.ca
4. Maughan, R.J. & Griffin, J. (2003). Caffeine ingestion and fluid balance: a review. Journal of Human Nutrition and Dietetics 16(6) 411–420
5. Wolf, R., Wolf, D., Rudikoff, D. & Parish, L.C. (2010). Nutrition and water: drinking eight glasses of water a day ensures proper skin hydration — myth or reality? Clinical Dermatology 28(4) 380–383
6. Palma, L., Marques, L.T., Bujan, J. & Rodrigues, L.M. (2015). Dietary water affects human skin hydration and biomechanics. Clinical, Cosmetic and Investigational Dermatology 8 413–421
7. Masento, N.A., Golightly, M., Field, D.T., Butler, L.T. & van Reekum, C.M. (2014). The British Journal of Nutrition 111 (10) 1841–1852
8. Sécher, M. & Ritz, P. (2012). Hydration and cognitive performance. The journal of nutrition, health and aging 16(4) 325–329
Bracha Kopstick is a Registered Dietitian in Toronto and owner of BeeKay Nutrition. She takes the “diet” out of dietitian, and wants you to take it out of your life! As a nutrition expert, Bracha promotes eating home-prepared foods more often and taking time to enjoy what you eat without any associated guilt. She is available for in-person and online counseling. Contact her at Bracha@beekaynutrition.com