Water, a solvent for biochemical reactions, has so many different physical properties and is so important for life. Water is the largest single constituent in the human body. It is essential in the absorption of metabolic heat in the body. It also, maintains vascular volume and aids in moving nutrients and wastes though the body. Water intake must be balanced with water loss on a daily basis in order to maintain a level of total body water. Total water intake consists of drinking water, the water in other beverages, and water in foods. Water deficits make it difficult to maintain homeostasis during perturbations and may have a negative effect on health. In an opposite but equal case, overconsumption of water and low sodium intake will lead to an excess of body water, resulting in hyponatremia and cellular edema.1
Either way too much or too little can have negative impacts on health. Despite the importance of proper water intake, there is still much confusion among the general public and most health care providers on the amount of water that should be consumed. This is because there hasn’t been sufficient evidence to support water intake recommendations as a means to reduce the risk for diseases. Instead, an Adequate Intake (AI) for total water intake was set in order to prevent acute dehydration which includes abnormal body and metabolic functioning. The AI was set based on the median total water intake from US survey data. From these surveys arose what is now considered the standard of 8 glasses of water a day.1 However, everyone’s needs are different and this is an important factor that shouldn’t be left out of the equation.
In humans, consuming fluids to replenish losses and satiate the thirst sensation that is generally partnered with dehydration is a natural process. The amount of liquid consumed usually matches up with the body’s deficit. This amazing bodily feat is still puzzling researchers. Recent evidence suggests that it has something to do with a natural swallowing inhibition. This proposal was tested by having participants rate their effort of swallowing while measuring regional brain responses when they were thirsty and after they had overdrunk. There was unwavering support for swallowing inhibition based on the effort rating recorded. There was a threefold increase in effort after over drinking water, but addition of 8% sucrose to the water had a minimal effect on the effort before and after the participant had over drank.2 It became increasingly difficult for the participants to swallow the more they drank, and the motor cortex that controls swallowing has to work harder in order for them to swallow. This didn’t happen when the participant were comfortable drinking and rated the experience as pleasant. These findings therefore consistently show a presence of swallowing inhibition after an excess of water has been consumed. This mechanism is thought to help regulate the overall fluid take in humans.3
The take home from all this is to forget the strict regimen of drinking a set amount of water every day. Instead, drink when you’re thirsty. Your body is smarter than you think and is good at maintaining balance if you listen to it.
- Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. The National Academies Press. https://www.nap.edu/read/10925/chapter/6. Accessed November 24, 2016.
- Saker P, Farrell MJ, Egan GF, et al. Overdrinking, swallowing inhibition, and regional brain responses prior to swallowing. Proceedings of the National Academy of Sciences. 2016;113(43):12274–12279. doi:10.1073/pnas.1613929113. http://www.pnas.org/content/113/43/12274.abstract. Accessed November 24, 2016.
- Roseveleth F, Eveleth R. New rule: Just drink when you’re thirsty. Smithsonian. http://www.smithsonianmag.com/smart-news/forget-your-hydration-rules-just-drink-when-youre-thirsty-180950290/. Accessed November 24, 2016.