Signs and symptoms of hyponatremia

Hyponatremia is an electrolyte imbalance defined by low blood sodium levels. Although it often requires medical attention, the earliest signs and symptoms can often be subtle and include muscle cramps, headaches, and fatigue. Symptoms (often neurological) get more severe as sodium levels continue to fall. 

Various medical conditions can cause hyponatremia, but so can overhydration with sodium-free fluids. For instance, when athletes drink too much plain water, blood sodium levels can drop, leading to exercise-associated hyponatremia. Hydration practices like drinking to thirst and including salt in fluids, especially during exercise, may help prevent this form of hyponatremia.

Today, I’ll dive into the signs and symptoms of hyponatremia to help you identify them in yourself and others, plus explain how drinking electrolyte water to thirst can help prevent it. Let’s get started.

What Is Hyponatremia?

A person is considered hyponatremic when blood sodium levels become diluted — specifically, when they fall below 135 mEq per liter. In other words, they have excess body water and insufficient solutes (aka, sodium) in their blood.

The human body typically is effective at preventing fluid and electrolyte imbalances. It’s always monitoring the osmolality (concentration of solutes) in your blood — and it’s always ready to make adjustments if things get wonky. Here are few examples:

• If blood osmolality is too high, your body increases sodium excretion through urine. Rising osmolality also triggers thirst, causing you to drink fluids that help restore fluid balance.
• If blood osmolality is too low, your body secretes aldosterone to reabsorb more sodium through the kidneys.
• If blood volume is too high — from, say, drinking too much water — your brain suppresses antidiuretic hormone (ADH) so you can pee out the excess water.

There are many more examples, but you get the idea. The takeaway? When the fluid balancing system runs properly, hyponatremia is rare. But this system can be derailed in a number of ways.

What Causes Hyponatremia?

When someone develops hyponatremia, it typically means that a medical condition has disrupted their blood balancing system, or their fluid balancing system has become overwhelmed.

In terms of medical conditions that can derail our fluid and electrolyte balance, the most common are kidney failure, heart failure, liver disease, cancer, and any illness that causes vomiting or diarrhea. Less common medical conditions include cystic fibrosis, Gitelman syndrome, Bartter syndrome, hypovolemic POTS, orthostatic hypotension, and Addison’s disease. Some drugs can also result in hyponatremia, including diuretics, oxytocin, SSRIs (antidepressants), nicotine, antipsychotics, NSAIDs (anti-inflammatories), and more. It can be worth talking with a trusted healthcare provider about whether your medical conditions or prescriptions could affect your fluid balance system, and how to prevent it in your unique situation.

The less-talked-about issue is drinking too much plain water. Consuming too much plain water, especially too fast, can overwhelm the body’s fluid balancing system and temporarily dilute blood sodium levels. Many elite endurance athletes have experienced this danger due to well-meaning but dangerous advice that more water is always better.

Exercise-Associated Hyponatremia

Drinking too much plain water can contribute to hyponatremia at any time. But doing so while exercising, when sweating fluids and electrolytes at high rates, can speed it up.

Part of the problem is that athletes are often encouraged to drink beyond thirst in an effort to prevent dehydration during intense efforts. Other factors may dilute blood sodium levels, too. For example, our bodies like to break down glycogen (the stored form of glucose, or sugar) for quick energy when exercising. Glycogen is stored alongside water molecules, and breaking glycogen down releases this stored water, which may contribute to fluid overload and decrease sodium levels in the blood. Exercise may also decrease the rate you urinate, making it harder to get rid of excess fluids. 

When you combine these factors with drinking plain water beyond thirst, it’s not surprising that up to 51% of endurance athletes wind up with asymptomatic cases of hyponatremia, and up to 1% of endurance athletes experience symptomatic hyponatremia — most commonly in ultra-endurance athletes like marathoners.

Signs and Symptoms of Mild Hyponatremia

Symptoms of mild hyponatremia (marginally low sodium levels) include:

• Headaches
• Brain fog
• Muscle cramps
• Low energy
• Fatigue

In other words, folks with mild hyponatremia may generally feel “off.” That said, these symptoms can overlap with many other conditions, including heat exhaustion, hypovolemia, hypoglycemia, and, ironically, dehydration.  It makes sense to seek the advice of a medical professional for proper diagnosis. However, since blood sodium tests aren’t always available on command, pay attention to the context. Was Johnny glugging plain water before his soccer game? Does he have exercise-associated hyponatremia symptoms, too? That might suggest a sodium imbalance is to blame.

Signs and Symptoms of Moderate to Severe Hyponatremia

Moderate to severe hyponatremia can have serious, neurological symptoms that can be life-threatening if left untreated. Here’s a list of what to look out for.

• Confusion
• Seizures
• Lethargy
• Light sensitivity
• Loss of consciousness
• Brain damage
• Brain swelling

In his book Waterlogged: The Serious Problem of Overhydration in Endurance Sports, Dr. Tim Noakes provides detail on his experience treating hyponatremic runners. The usual presentation, according to Noakes, is confusion, loss of consciousness, and epileptic seizures. “The other presentation that I frequently see is that people who finish the race become very withdrawn,” Noakes is quoted as saying. “They lie down in the fetal position. They don’t want to speak to anyone. They don’t want to look at the lights.”

In these moderate to severe cases, medical attention should be sought immediately. Along with restricting fluids and halting exercise, a doctor may give the patient super salty fluids, either orally or through an IV. Often, this can restore the patient fairly rapidly.

Tips To Prevent Exercise-Associated Hyponatremia

Two tips to help maintain fluid balance and prevent exercise-associated hyponatremia are to drink to thirst and include sodium in your fluids. Let’s cover both strategies. 

Thirst is nature’s built-in system for maintaining fluid balance. If you need more fluids, you get thirsty and drink more water. If you don’t need more fluids, thirst shuts down and you stop drinking water. Therefore, drinking to thirst — not beyond — may decrease the risk of overhydration and low blood sodium levels during activity. 

Including sodium in those fluids may also help keep blood sodium levels in a healthy range, particularly during exercise when we’re sweating (sodium is the most predominant electrolyte lost in sweat). Adding about 1 gram of sodium per liter of water can replace average sodium losses through sweat, but your mileage may vary and it can be worth testing different ratios out and seeing what works best for you.

To recap, drink salty fluids to thirst throughout exercise, and you’ll be hydrating wisely and supporting fluid balance. And remember that overhydration is just one cause of hyponatremia — you may need to dig more. I hope this article helps!