What is hyponatremia? Hyponatremia is low sodium in the blood, typically below 135 mEq/L [135 mmol/L]. Yes, hikers can get it by drinking more water than the body can handle, especially during long, hot, sweaty days. It can turn serious fast when confusion, vomiting, seizures, or collapse appear.
What is hyponatremia?
Hyponatremia means your blood sodium level has dropped too low.
Sodium helps control fluid balance, nerve signals, and muscle function. When sodium falls, water shifts into cells. In mild cases, you may feel lousy and foggy. In severe cases, brain swelling can trigger confusion, seizures, coma, or death. Mayo Clinic gives a clear medical overview of hyponatremia symptoms and causes, including nausea, headache, confusion, and loss of energy.
For hikers, the trail-specific version is usually called exercise-associated hyponatremia, or EAH. The Wilderness Medical Society guidelines on exercise-associated hyponatremia define it as hyponatremia that happens during or up to 24 hours after physical activity. Translation: you can feel fine at the trailhead, keep chugging water all day, and get into trouble later at camp or in the car.
Can drinking too much water cause hyponatremia?
Yes, drinking too much water can cause hyponatremia when intake outruns your body’s ability to get rid of fluid.
That old advice to “drink before you’re thirsty” gets hikers into trouble when it turns into forced drinking. A slow hiker on a hot climb may sip constantly because the bottle is there, the bladder hose is easy, and everyone has heard horror stories about dehydration. But your kidneys can only dump water so fast, and hard exercise can make the body hold onto water through antidiuretic hormone.
The CDC Yellow Book says the idea that you “can’t drink too much” during prolonged exercise is outdated and dangerous, and that prevention includes drinking enough to relieve thirst. See the CDC’s travel medicine section on heat illness and exercise-induced hyponatremia.
Here’s the trap: you sweat out water and sodium, then replace mainly water. Over hours, your blood gets diluted. A salty snack helps, but food cannot magically cancel out gallons of extra water.
What are the symptoms of hyponatremia in hikers?
Hyponatremia symptoms can look like dehydration, heat exhaustion, altitude illness, or plain fatigue.
That overlap is why hikers miss it. A tired, nauseated person on a hot trail looks dehydrated. The reflex is to hand over water. If the real problem is low sodium from overdrinking, more plain water can make things worse.
| Condition | Common clues | What can confuse you |
|---|---|---|
| Hyponatremia | Headache, nausea, vomiting, bloating, swollen hands, confusion, worsening symptoms after lots of fluid | Can look like heat illness or dehydration |
| Dehydration | Thirst, dry mouth, low urine output, dizziness, dark morning urine | A dehydrated hiker may also feel nauseated and weak |
| Heat exhaustion | Heavy sweating, weakness, dizziness, headache, nausea, elevated body stress from heat | Early symptoms overlap with hyponatremia |
Red flags matter most. Confusion is not normal trail tiredness. Repeated vomiting is not “just a rough day.” Trouble walking straight, fainting, seizure, or loss of consciousness means the hike is over and medical help is needed.
Why do hikers get hyponatremia on long trails?
Hikers get hyponatremia when long exertion, heat, sweat loss, and overdrinking line up.
Long days create the setup. You’re moving for 6, 8, 10, or more hours. You sweat. You snack less than usual. You may drink from a hydration bladder without tracking how much is gone. You may also be moving slowly, so you’re drinking like an endurance athlete while burning energy at a lower rate.
Risk rises when you:
- Drink on a rigid schedule even when you are not thirsty.
- Carry only plain water on long, hot days.
- Refill a large bladder and sip constantly without noticing total intake.
- Eat very little salty food during long efforts.
- Keep pushing after nausea, headache, or confusion starts.
- Assume every sick hiker needs more water.
The Wilderness Medical Society notes that most EAH cases involve too much total body water relative to sodium during endurance events and strenuous wilderness activity. That is exactly the kind of slow-burn mistake a hiker can make on a canyon route, desert traverse, humid Appalachian climb, or high-mile backpacking day.
How much water should you drink while hiking?
Drink to thirst, then adjust for heat, effort, altitude, and your own sweat rate.
No single bottle-per-hour rule fits every hiker. A 115-pound [52 kg] hiker cruising in cool shade does not need the same fluid as a 210-pound [95 kg] hiker climbing in direct sun. Your pace, pack weight, humidity, wind, temperature, and fitness all matter.
Use this trail method instead:
- Start normally hydrated. Pale morning urine and normal thirst are useful clues. Do not pre-load with huge amounts of water.
- Carry enough, not endless. Plan water around distance between reliable sources, weather, and bailout options.
- Drink when thirsty. Sip, don’t force. Thirst is useful during most hiking situations.
- Eat real trail food. Mix sweet foods with salty options like crackers, pretzels, salted nuts, jerky, cheese, or soup.
- Track bladder use. If you use a hydration reservoir, check it at breaks so you know whether you drank 16 oz [0.5 L] or 70 oz [2.1 L].
- Pause when symptoms show up. Nausea, headache, swelling, or confusion deserves a stop, shade, reassessment, and a safety plan.
Do electrolytes prevent hyponatremia?
Electrolytes can help replace sodium, but they do not make overdrinking safe.
This is where marketing gets hikers. A flavored electrolyte packet may contain sodium, but if you wash it down with too much water, your blood sodium can still fall. Sports drinks are often more dilute than your blood. They are not a shield against nonstop sipping.
Food is often the easiest sodium source on trail. Salty snacks are packable, familiar, and less likely to upset your stomach than harsh salt-loading strategies. The CDC also points hikers toward salty foods during prolonged exertion rather than relying only on drinks.
A smart electrolyte plan looks simple:
- Bring salty food for hikes lasting several hours.
- Use electrolyte drinks as part of your plan, not as permission to overdrink.
- Avoid trying a new high-sodium product for the first time on a remote hike.
- Be extra cautious if you have kidney, heart, liver, adrenal, or blood pressure issues, or if you take medications that affect fluid balance.
What should you do if you suspect hyponatremia on trail?
Stop, reassess, and get medical help for severe or worsening symptoms.
You cannot confirm blood sodium by guessing. A real diagnosis requires lab testing, such as a blood sodium test described by NIH MedlinePlus. On trail, you are making safety decisions with incomplete information.
Use this field checklist:
- Stop hiking. Continuing can worsen both heat illness and hyponatremia.
- Get out of heat. Move to shade, loosen layers, and cool the person if overheated.
- Do not force fluids. If the person has been drinking heavily and shows concerning symptoms, more water may be harmful.
- Offer salty food only if alert and able to swallow safely. Do not give food or drink to someone confused, vomiting repeatedly, drowsy, or unconscious.
- Call for help. Confusion, seizure, collapse, severe headache, repeated vomiting, or worsening condition needs emergency care.
Do not try to fix a severe case with salt tablets, chugged broth, or internet math. Severe hyponatremia is a medical emergency.
When to see a doctor
See a doctor promptly if symptoms suggest hyponatremia, especially after long exercise or heavy fluid intake.
Emergency care is needed for confusion, seizures, loss of consciousness, severe weakness, trouble breathing, or repeated vomiting. Mayo Clinic’s hyponatremia diagnosis and treatment guidance says serious symptoms such as vomiting, confusion, seizures, or lost consciousness require emergency care.
You should also talk with a clinician before big hiking trips if you have a history of low sodium, kidney disease, heart failure, liver disease, adrenal problems, or you take diuretics, antidepressants, seizure medicines, or other medications that can affect sodium and fluid balance. No trail article can clear you medically. Get personal advice before you are 9 miles [14.5 km] from the trailhead.
How can you prevent hyponatremia while hiking?
Prevent hyponatremia by avoiding forced overdrinking and pairing long efforts with food that includes sodium.
The goal is balance. Not bone-dry suffering. Not a sloshing stomach. Balance.
- Drink to thirst instead of chasing a fixed hourly target.
- Plan water carries by route, heat, exposure, and reliable sources.
- Eat salty snacks during long hikes, especially in heat.
- Take real breaks so you can notice symptoms before they snowball.
- Teach your hiking partners that sick plus overhydrated is different from simply thirsty.
- Know turnaround points. Pride is a lousy treatment plan.
If you remember one thing, make it this: dehydration is common, but overhydration can be dangerous too. Your job is not to drink the most water. Your job is to finish the hike with your brain, legs, and judgment working.
Related reading
- Lyme Disease Symptoms After a Hike
- Hantavirus and Camping: Cabins, Shelters and Risk
- Electrolytes for Hikers: What They Are and How Much You Need
- What Does Poison Ivy Look Like? Leaves of Three and Lookalikes
FAQ
What is the first sign of hyponatremia?
Early signs can include headache, nausea, low energy, weakness, and feeling “off.” These symptoms are vague, so look at the context: long exertion plus heavy fluid intake raises concern.
Can you get hyponatremia from drinking water after a hike?
Yes, hyponatremia can appear after exercise, not only during it. Exercise-associated hyponatremia can develop up to 24 hours after activity, so worsening nausea, headache, confusion, or vomiting after a long hike deserves medical attention.
Are swollen hands while hiking a sign of hyponatremia?
Swollen hands can happen for several reasons, including normal fluid shifts during hiking. But swollen hands plus headache, nausea, bloating, confusion, or heavy water intake is more concerning.
Should I take salt tablets to prevent hyponatremia?
Do not rely on salt tablets as your main prevention plan. Drinking to thirst and eating salty foods during long hikes is usually a safer, more practical approach for recreational hikers.
Is hyponatremia the same as dehydration?
No, they are different problems, though symptoms can overlap. Dehydration is too little body water, while hyponatremia is too little sodium in the blood, often from too much fluid relative to sodium.
Can electrolyte drinks cause hyponatremia?
They can contribute if you drink too much of them. Many electrolyte drinks still contain mostly water, so overdrinking them can dilute blood sodium just like overdrinking plain water.