The signs and symptoms of hyponatremia can be subtle. If you don’t know what you’re looking for, you can slog away for years in a suboptimal state.
I see it all the time in active folks. They lose both sodium and fluids through sweat, but they mainly focus on replacing the fluids. Electrolytes are, at best, an afterthought.
That’s a recipe for hyponatremia. Drinking too much plain water causes blood sodium levels to fall—leading to muscle cramps, fatigue, low energy, and other hyponatremia symptoms. “Plain” is the operative term here. If you put sodium in your water, you avoid these complications.
I wish I knew that twenty years ago. Back then, I was wondering where my energy and focus had gone on the jiu-jitsu mat. Even though I was sweating like a warthog being chased by a panther, I didn’t suspect electrolytes were the problem. As many do, I figured I was getting enough dietary sodium to cover sweat losses.
But as it turned out, I was wrong. When I bumped up my salt intake—first with electrolyte homebrews and later with LMNT—it lit me up like a Christmas tree. I hit a higher gear both on and off the mat.
The off-mat benefits were the real gift. My cognition sharpened up. I felt brighter and clearer. My brain fog vanished. And looking back, it makes sense. Since sodium is crucial for brain function, the hallmarks of hyponatremia are neurological.
Today I’ll be diving into the signs and symptoms of hyponatremia. This will help you identify these symptoms in yourself and others so you can take corrective measures.
What Is Hyponatremia?
Hyponatremia is a condition of low serum sodium. According to most sources, a person is considered hyponatremic when blood sodium levels fall below 135 milliequivalents per liter.
Ultimately, hyponatremia is a problem of fluid balance. When someone has low sodium levels, it means they have excess body water—and insufficient solutes (aka, sodium)—in their blood and tissues.
Normally, the human body excels at preventing fluid imbalances. It’s always monitoring the osmolality (electrolyte concentration) in your blood—and it’s always ready to make adjustments if things get wonky.
Here are some examples:
- If blood osmolality is too high, your body increases sodium excretion through urine. Rising osmolality also triggers thirst. Then you drink water and fluid balance normalizes.
- If blood osmolality is too low, your body secretes aldosterone to reabsorb more sodium through the kidneys. Aldosterone also raises blood pressure. (Dang.)
- If blood volume is too high—from drinking too much water, say—your brain suppresses antidiuretic hormone (ADH) so you can pee out the excess.
There are many more examples, but you get the idea. When the fluid balancing system runs properly, hyponatremia is rare. But this system can be derailed.
What Causes Hyponatremia?
When someone has hyponatremia, it means that either:
- Something is wrong with their fluid balancing system
- Their fluid balancing system has become overwhelmed
To the first point, various medical conditions can derail the fluid balancing system. The most common are kidney failure, heart failure, liver disease, cancer, Addison’s disease, and any illness that causes vomiting or diarrhea.
Many drugs also result in hyponatremia. This list includes diuretics, oxytocin, SSRIs, nicotine, antipsychotics, NSAIDs, and even illicit drugs like MDMA (ecstasy).
Those are the medical causes, but I spend more time thinking about cause number two: drinking too much plain water. When you over-hydrate with sodium-free water, you overwhelm the fluid balancing system.
The overwhelm is temporary, but it can be dangerous. Many elite endurance athletes have experienced this danger firsthand.
Elite endurance sports create the perfect storm of hyponatremia risk. To begin, the setting is engineered to promote overhydration. Not only are elite athletes encouraged to drink beyond thirst by “reputable” organizations like the American College of Sports Medicine, but they’re given ample opportunities to do so.
Most marathon courses have watering stations every couple of miles. This water, unfortunately, does not contain salt. Meanwhile, the competitors are sweating excessively. In warm climates, athletes can lose up to 7 grams of sodium per day!
Then there’s ADH. When you over-hydrate, the body usually suppresses ADH so you can pee out the excess. Unfortunately, this ADH-suppression mechanism gets broken by exercise. The result is unwanted fluid retention and hyponatremia.
The last one I’ll mention is glycogen metabolism. As you chew through stored glucose (glycogen) during exercise, a significant amount of water is released that may dilute sodium levels.
When you combine these factors, it’s not surprising that around 15% of elite endurance athletes develop hyponatremia. They stagger across the finish line. They act like confused zombies. They need to be rushed to the medical tent. Occasionally, they die. Those are the worst cases, of course. But even mild hyponatremia can be life-deranging.
Signs and Symptoms of Mild Hyponatremia
A person with marginally low sodium levels will often present with headaches, muscle cramps, low energy fatigue, brain fog, and malaise. They’ll feel “off”, in other words.
I see a lot of people cycling in and out of mild hyponatremia. Why? Because bad hydration advice is ubiquitous. Many have heard the age-old advice to drink 8 glasses of water per day, regardless of thirst. This rule is inimical to healthy hydration, but it’s been drilled into our psyche since kindergarten.
When you drink too much plain water, your body can’t keep up. And it really can’t keep up if you combine it with sweaty exercise. And don’t forget about diet. If you’re a health-conscious person eating a real food diet, you probably aren’t getting enough sodium.
Most people get their salt from processed foods. You, however, must rely on the salt shaker. And if your whole food diet is also a low-carb diet, then you really need more sodium. When you limit carbs, the drop in insulin increases urinary sodium excretion.
Sum these hydration and dietary factors and you have a formula for mild hyponatremia. Let’s see what happens when sodium levels continue to fall.
Signs and Symptoms of Moderate to Severe Hyponatremia
Moderate to severe hyponatremia is serious stuff. It’s a life-threatening condition that has killed more than a few athletes.
In his book Waterlogged: The Serious Problem of Overhydration in Endurance Sports, Dr. Tim Noakes covers many of the points I just covered and more. His accounts of treating hyponatremic runners are super interesting.
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.”
Why does this happen? Because low sodium causes brain swelling. It’s a neurological nightmare. Fortunately, treatment with oral or IV sodium restores the patient fairly rapidly.
For those of you who like lists, here’s a list of moderate to severe hyponatremia symptoms:
- Light sensitivity
- Loss of consciousness
- Brain damage
- Brain swelling
I’ll cover hyponatremia treatment and prevention soon. First, I want to talk about sodium deficiency.
Hyponatremia and Sodium Deficiency
By itself, a dietary sodium deficiency won’t cause hyponatremia. Allow me to elaborate.
Remember your fluid balancing system? If you don’t get enough sodium, your body secretes hormones like aldosterone, renin, and angiotensin to retain this mineral. These hormones may raise blood pressure (yikes), but they’re effective at keeping sodium around.
Another consequence of a low sodium diet? Osteoporosis. That’s right. If you chronically under-consume salt, your body will raid bone to keep serum levels up.
That’s why sodium deficiency won’t show up on a blood test. Serum sodium is insured by skeletal sodium. But this doesn’t mean sodium intake doesn’t influence hyponatremia risk. It does. Consuming salt doesn’t only prevent hyponatremia, but it also treats it.
How To Prevent Hyponatremia
Barring medical considerations, there are only two rules for preventing hyponatremia:
- Drink when thirsty
- Get enough sodium
Thirst is nature’s way of simultaneously preventing dehydration and overhydration. It’s a brilliant mechanism for maintaining fluid balance. Athletes who drink to thirst don’t typically develop hyponatremia. Athletes who drink on a set schedule or as much as they can are the more likely group.
The second rule is to stay salty. Most people will benefit from a baseline of 4–6 grams of sodium (2–3 teaspoons of salt) per day, but super sweaty athletes may need double or triple that amount to replace sweat losses.
The salt shaker is your friend here, but it’s probably not enough. That’s why I recommend adding salt to your water for an extra hit of sodium. That’s the basic principle behind LMNT, my tasty electrolyte drink mix. It’s designed to keep active people hydrated and non-hyponatremic.
And in case you were wondering, the science on salt is solid. In one 2014 randomized controlled trial, drinking saltwater reversed hyponatremia in runners who had just completed a 161-kilometer race.
To recapitulate: drink to thirst, get enough salt, avoid hyponatremia, feel better. It really is that simple.