by Tim Curry, MS ACSM-RCEP

Water is an essential molecule for human health, wellness, and performance. It is something that most of us don’t consume enough of, but did you know you can drink too much water? Though far less common than dehydration, hyponatremia (aka water intoxication) is just as dangerous. We will focus on one specific type of hyponatremia (more common in sports), Exercise Associated Hyponatremia (EAH). Let’s explore what EAH is, how it happens and how to prevent it.

TIME FOR SOME LATIN

Have you ever looked at a periodic table and noticed sodium’s symbol is “Na”? The Latin word for sodium is natrium (hence Na). You may notice that this word also shows up in hyponatremia which means low (hypo-) sodium (-natremia). The issue that occurs with water intoxication is an imbalance of the electrolyte sodium, between fluid filled spaces in your body.

WHAT DO ELECTROLYTES DO?

Electrolytes are used in our body to help control the flow of water in and out of cells. To conceptualize this idea, imagine two boxes filled with water and some sodium. Between these boxes is a membrane, or a wall, that allows water through, but not sodium.

Now in this example, as in our body, the exact amount of water molecules and sodium molecules is not the same between the boxes. One box has more water molecules in it and fewer sodium molecules.

This creates what is called a concentration gradient between the boxes. The water wants to move from where it is in a high amount to the box where it is in a lower amount. The water will move across the membrane until the two sides equalize.

Imagine if we added more sodium to the box that has less total water, we could cause the water to move back the other way. This is the same basic principle that allows our body to shift water in and out of cells in our body. It is controlled by the amount of electrolytes found between the fluids.

WHAT IS HAPPENING TO ME?

Hyponatremia is an issue where you have too little sodium in the blood stream. This causes water to flow into cells and out of the blood stream. While fluid movement between cells is not generally a concern, excessive fluid movement caused by hyponatremia is very detrimental to the body. When our sodium levels fall too low our cells begin to take on far too much water, causing them to expand. This expansion pushes against other cells, nerves, arteries/veins/capillaries, and can eventually lead to the cell’s own walls bursting.

SO THIS ONLY OCCURS WHEN I DRINK TOO MUCH WATER, RIGHT?

Not quite, remember the root issue is too little sodium. While overconsumption of water is a main factor of hyponatremia, especially during exercise, there are a couple other causes. One main issue is the inappropriate secretion of a hormone call antidiuretic hormone (ADH). ADH helps control how our kidneys function, and how much water we excrete (i.e., urinate). When we create more of it, our kidneys help us retain more water, and vice versa. Normally, if we are becoming dehydrated, we create more ADH and if we are overhydrated, we reduce production. In this case though, ADH is being produced even though we don’t need it, causing us to hold on to too much water and diluting the sodium in our bloodstream.

An inappropriate secretion of ADH occurs for several reasons, but some to be aware of include stress, pain, heat, and use of NSAIDs, all of which are common elements in many sports. Additionally, there are some less common reasons we would have low sodium levels in the bloodstream that we will not discuss here.

IF LOW SODIUM LEVELS ARE THE ISSUE, CAN’T I JUST DRINK SPORTS DRINKS WITH ELECTROLYTES OR EAT SALT TABLET? PROBLEM SOLVED…WHERE IS MY PHD?

While drinking fluids with electrolytes proactively to stay hydrated is great, once hyponatremia is reached, it becomes a bit more complicated. Sports drinks are generally hypotonic solutions. This means that they are designed to help get water from the gut into your body quickly. They do contain some sodium, but not enough to correct this issue. Instead, they are potentially exacerbating the issue by allowing water to get into the blood stream even faster.

Salt tablets are potentially problematic due to their unintended side effect of increasing thirst. While placing more sodium into the blood would help, the issue is that people who take salt tablets tend to consume even more water. Sports drinks and salt tablets have not been shown to reduce hyponatremia risk, and in fact they may make things worse.

IN THAT CASE, WHAT IS THE SOLUTION?

Focus on simple, proper fluid intake strategies. The most effective solution is to simply follow a proper fluid intake strategy for your training and racing. When exercising, you should not experience weight gain during the activity. We also don’t want to lose more than 2% of pre-activity weight either. Just like in Goldilocks, the goal is to find the consumption amount that is just right.

You can do this by weighing yourself before and after activity (nude if possible because clothing can retain water and add weight to your post-activity weigh in). If you gained weight after the activity then drink less water next time, and vice versa. A good place to start is to consume 16–24 oz of fluid per hour of activity. Another approach is to drink to thirst, but still check that you are not under or over consuming. You can also add in urine color monitoring. The ideal hydration level will lead to a pale-yellow urine color. Take caution if your urine color becomes excessively dark or clear.

WHEN DO I NEED TO WORRY ABOUT EAH?

The risk for EAH depends on the sport, for example rowers generally show the highest rate of this issue overall. In endurance sports there appears to be a correlation between running distance and risk; the longer you are out there the higher the risk. Cyclists have a low risk for EAH, relatively speaking. The overall risk of EAH occurring in a sport ranges from 0% up to as high as 51% in certain cases based on the research.

As a general guideline you should be aware of EAH being a risk if you are:

· Exercising for long durations (3–4+ hrs)

· Not prepared for your event

· Exercising in an environment that is very hot, cold, or humid

· Taking NSAIDs

· A female

· A person who has not developed a hydration plan and tends to go crazy with drinking water during exercise

HOW DO I KNOW IF I HAVE IT?

The signs of EAH can be confusing for people when taken out of context because they can mirror those of dehydration. Nausea, vomiting, dizziness, oliguria (low or no urine production), muscle cramps, and fatigue are all symptoms that belong to each issue. However, the change in weight is a clear sign of EAH.

Due to the serious nature of both dehydration and EAH, if you experience symptoms of either, it is important you seek professional medical advice ASAP. Since dehydration and EAH, along with other medical issues, can all present similarly, but warrant different individual treatments, you should seek trained medical advice to resolve the issue. The best way to avoid these issues is with the creation and execution of a hydration plan that works for you. With just a little bit of work you can easily manage the risks of water intoxication.

If you are interested in learning more about hydration and the application of science-focused nutrition while working with athletes, check out the nutrition courses developed by registered dietitian Mary Ginnetti. Coeus courses were developed along-side the National Interscholastic Cycling Association (NICA) to meet the needs of high school cycling coaches. Coeus courses are also relevant to people interested in athletic nutrition, performance, or skills training. 

SOURCES

Rosner, M. H., & Kirven, J. (2007). Exercise-Associated Hyponatremia. American Society of Nephrology(2), 151–161.

Scheer, W., & Knechtle, B. (2020). Exercise associated hyponatremia in endurance sports: a review. Archivos de Medicina del Deporte, 37(4), 260–265