Considering that the human body is upwards of 60% water maintaining adequate hydration is fundamental to good health. With so many enticing energy drinks fruit juices bottled tea and coffee on the market humble life-sustaining plain ol’ water sometimes gets forgotten.

Dehydration has disastrous effects. Water is so critical to processes throughout the entire body that when there isn’t enough to go around the body may perform a kind of triage prioritizing the use of water in some systems while causing shortages or imbalances elsewhere. Due to water’s role as a constituent of blood digestive secretions synovial fluid (which cushions the joints) cerebrospinal fluid and more insufficient hydration can lead to acute as well as chronic health problems including some that may be life-threatening.

You have probably heard the advice to consume at least eight-8oz glasses of water daily just to maintain a baseline of adequate hydration and then consume additional amounts if you are physically active or if the weather is hot and dry. If you’re trying to lose weight you may even be following suggestions to “fill up” on water in an effort to consume fewer calories from food. Unfortunately overhydration from drinking too much water can result in complications just as dangerous and deadly as those of dehydration. And overhydration is no longer a very rare occurrence limited to marathon runners and other endurance athletes. It’s happening even among high school athletes and there have also been fatal incidents of overhydration resulting from university fraternity hazing rituals and bizarre radio contest challenges.

The most significant result of overhydration is hyponatremia which is a medical term that translates to “low sodium in the blood.” This does not necessarily mean that the absolute amount of sodium is low; it may be that the amount of sodium in the blood is normal but the amount and rate of water intake has surpassed the body’s ability to maintain proper osmotic balance and the concentration of sodium has been diluted by too much water. The body keeps a higher concentration of sodium in the blood and other fluids that are outside of cells than it does inside cells. When excess water has diluted the sodium concentration in these fluids the body will try to restore its osmotic balance by having cells take in the extra water. This leads to tissue swelling including in the brain which is why this condition must be taken seriously and may require immediate medical attention.

The signs and symptoms of overt hyponatremia are weakness dizziness confusion headache nausea and/or vomiting. Due to the effects on the brain extremely severe cases may result in seizures coma and even death. Hyponatremia can be an effect of specific medical conditions but when it is the consequence of deliberate or inadvertent consumption of excessive amounts of water the other name for hyponatremia—water intoxication—emphasizes just how dangerous a situation it can be. 

So how do you stay hydrated without risking overhydration? Let thirst be your primary guide. The often-repeated saying that if you’re thirsty it’s already too late is incorrect. Common sense should be a guide too. If you’ve been sweating significantly consider replacing water and electrolytes either with a beverage specifically formulated for that purpose or by adding a pinch of unrefined salt to your water or food. 

According to the 2015 consensus statement regarding exercise-associated hyponatremia (EAH) published in the Clinical Journal of Sport Medicine “The safest individualized hydration strategy before during and immediately following exercise is to drink palatable fluids when thirsty. Studies verify that participants allowed free access to fluids during treadmill walking in the heat or running 30 km under different ambient conditions maintain plasma osmolality by drinking to thirst.” In other words drink when you’re thirsty but don’t feel pressured to “pre-game” by guzzling copious amounts of water in advance of physical exertion.

The experts agree: there is no need to engage in “protective hydration” above and beyond normal water consumption. As with all vital nutrients you can get too much of a good thing. Adequate water is essential but that doesn’t mean more is always better. 

Sources: 

1. Ballantyne C. Strange but True: Drinking Too Much Water Can Kill. Scientific American. 21 June 2007.
2. University of Connecticut Korey Stringer Institute. Hyponatremia.
3. Hew-Butler T et al. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference Carlsbad California 2015. Clin J Sport Med. 2015 Jul;25(4):303-20.