The Science Of Hydration & Hyponatramia With Dr. Tamara Hew-Butler
“Thus, to answer your question, the definition of “dehydration” is confusing because there are so many conflicting different definitions of the same term. Overhydration is when there is excess water in the system (our bodies) or more than what is needed. Overhydration usually results in peeing a lot (getting rid of the excess fluid ingested) but in rare cases, it can be fatal.”
—Dr. Tamara Hew-Butler
In the ever-evolving landscape of sports medicine and exercise physiology, understanding the nuances of hydration and its impact on performance is paramount. Dr. Tamara Hew-Butler, a distinguished podiatric physician and associate professor at Wayne State University, Detroit, Michigan, stands at the forefront of this field, unraveling the complexities of hydration science with unwavering dedication and expertise.
With a distinguished academic journey spanning institutions like the University of California at Los Angeles, Temple University, and the University of Cape Town, Dr. Hew-Butler has emerged as a leading authority in exercise-associated hyponatremia and the intricate mechanisms governing water and sodium balance. Her groundbreaking research has not only garnered acclaim within academic circles but has also transcended traditional boundaries, captivating audiences on radio shows, television programs, and esteemed publications worldwide.
In this exclusive interview, we delve into the depths of hydration science with Dr. Tamara Hew-Butler, exploring the multifaceted nature of dehydration, overhydration, and the risks associated with hyponatremia. With her invaluable insights, we aim to demystify common misconceptions surrounding hydration, empower individuals to make informed decisions about their fluid intake, and ultimately optimize performance and well-being. Join us as we embark on a journey into the realm of hydration and hyponatremia, guided by the expertise of one of the foremost authorities in the field.
6 Questions With Tamara Hew-Butler
1. Can you talk about what dehydration and overhydration are?
There are three main (and conflicting) definitions of “dehydration”, which makes subsequent hydration advice (i.e., how much water should I drink) confusing and often conflicting. The three definitions are as follows:
The clinical and physiological definition of dehydration refers to cellular dehydration and is defined when enough water is lost so that the fluids surrounding the cells become concentrated (“hypertonic” is the correct term). When this happens, the cells begin to shrink (as the water inside the cells flows to the outside of the cell, down an osmotic gradient, due to the hypertonic environment). With “cellular dehydration” the shrinking of the cells triggers thirst so that more water is put back into the body, so equilibrium (fluid homeostasis) is re-established. A diagnosis of cellular dehydration can only be confirmed through a blood test(i.e., a blood sodium concentration >145mmol or plasma osmolality >296mOsm/kgH2O). Behavioral drinking from the physiologic sensation of thirst serves to rectify (and prevent) cellular dehydration.
The second definition of dehydration is commonly used in sports medicine, because it is easily diagnosed using body weight and/or urine concentration. When an athlete loses >2% of (starting) body weight during exercise, this signifies “dehydration”. Alternatively, a urine specific gravity (USG) >1.020 signifies dehydration, from this sports medicine perspective. Because body weight and urine are not direct physiological measures of hypertonicity (cellular dehydration) thirst is not activated by these indirect measures. This is why you hear “when you get thirsty it is too late” because bodyweight loss and urine concentration do not reflect what is going on in the blood (the regulated variable). Please see this article, if you want to learn more.
The third definition of dehydration is what I call the “commercial definition” of dehydration because it isn’t based on science but rather from press releases put out by companies performing surveys. As such, the statistic that 75% of children are walking around dehydrated comes from a survey of parents (sponsored by soda stream) which asked the parents whether or not their kids drank at least 8 glasses of water a day. If the parent answered no, these children were considered “dehydrated”. The International Bottled Water Association also surveyed 3003 adults (asking the same question in 1998) which is how up to 75% of adults walk around dehydrated came about.
Thus, to answer your question, the definition of “dehydration” is confusing because there are so many conflicting different definitions of the same term. Overhydration is when there is excess water in the system (our bodies) or more than what is needed. Overhydration usually results in peeing a lot (getting rid of the excess fluid ingested) but in rare cases, it can be fatal.
2. What is hyponatremia? What are the symptoms and the risks associated with it?
Hyponatremia is biochemically defined as a blood sodium concentration below the normal range of the test, which is usually <135mmol/L. Basically, when too much water is administered (beyond the ability of the kidneys to excrete the excess water, as urine) the excess water “dilutes” the sodium ions in the blood (like pouring more whiskey over the same amount of rocks).
This “hypotonicity” from drinking too much fluid (or from the administration of too much IV fluids in a hospital setting) causes all the cells in the body to swell (the opposite of cellular dehydration, where all the cells shrink due to hypertonicity).
Hyponatremia gets dangerous when the brain swells more than 5-8%, pushes against the skull, and causes brainstem herniation (i.e., pushed the brainstem out of the base of the skull) and the patient dies.
Unfortunately, the signs and symptoms are very similar to dehydration and include headache, nausea, vomiting, and confusion. People with hyponatremia feel and look “puffy” from all the cell swelling and are rarely thirsty.
3. How much water should we drink a day?
There is no “one size fits all” regarding the amount of water people need to drink per day (like there is no set number of calories we all need to eat to be healthy). The amount of water a person needs per day varies widely and is highly dependent on size (bigger people need more water than smaller people), activity level (the higher intensity you exercise the more you sweat), and ambient temperature (the hotter it is the more you sweat). Basically, the more we sweat the more water we lose, which needs replacing. Thus, in general, it is the amount of water that we lose is what dictates how much water we need to replace (drink) and not the other way around.
4. I have one foot in the world of working with patients with disabilities and chronic health conditions who seem to be underhydrated and another in the world of fitness where overhydration is the concern. What are some strategies to know if we’re getting too little or too much water throughout the day?
As per the above, whether you are big or small, fast or slow, disabled or able-bodied, when we get thirsty we should drink and when we are not, we do not need the excess water. Drinking fluids when thirsty will maintain proper hydration levels (prevent dehydration AND overhydration) in most situations in most individuals (and animals!). The sensation of thirst arises from sensors in the brain that are constantly “sampling” the blood for the perfect balance and water and salts (tonicity). Fluid balance is a physiologically regulated variable (when cells start to shrink), just like hunger (when the stomach shrinks) and the urge to urinate (when the bladder is full). There is no better “app” or “tracker” than the osmosensors located in the circumventricular organs within the brain (just outside the blood-brain barrier).
Brian: two strategies I use with my patients to help teach them about their current hydration level is how dry their tongue is and the color of their pee.
5. With the popularity of fashionable water bottles like Stanleys and Hydroflasks, do you believe that the trend of frequent water sipping might impair our ability to discern genuine thirst signals?
I don’t think the physiological sensation of thirst will ever get “impaired” by chronic drinking during the day. People tell me they “never get thirsty” and believe that their thirst sensation is indeed impaired. However, in reality, since they never need water (always in an excess water balance state and always peeing) thirst never needs to be triggered. I then tell these individuals that if I took away their water and made them exercise in the heat for a few hours, they will know what thirst feels like!!
With that said, people who are chronically sipping out of their water bottles do seem to get “thirsty” when they DO NOT have their bottle. I think this is more from the sensation of wetness on their lips being gone than actual physiological thirst (as thirst can be triggered by a dry mouth, and is called xerostomia) and warrants further study!
6. Talk about the importance of electrolytes for our health.
I think you covered this well [in your article on electrolytes]!! The only comment I will add is that water, minerals, and nutrients are usually replaced adequately during meals. The mainstream media (and culture of impatience) makes us believe that we need to replace every drop of water and salt lost through sweat instantaneously. We have mechanisms in place that keep water and salt in balance despite changes in climate and activity.
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