Hyponatremia at work: when more water hurts

What is hyponatremia?

Hyponatremia means low sodium in the blood. In exercise-associated hyponatremia (EAH), a 2025 review in the Journal of Endocrinological Investigation says the primary cause is overconsumption of fluids, which dilutes the sodium concentration in the blood. In plain words, the worker drinks more than the body needs.

It is not the same as dehydration. Dehydration is too little water. Hyponatremia from overdrinking is too much water for the sodium on hand. Both can feel bad, and the fix for one can make the other worse. That is why a crew needs a pace and a ceiling, not just “drink more.” See hyponatremia and dehydration in the glossary.

Can workers really get it on the job?

Yes. A 2019 review in Transactions of the American Clinical and Climatological Association says it is likely that anyone in prolonged physical activity who drinks copious amounts of fluids is at high risk. The 2025 review adds that EAH was first considered limited to extreme endurance events such as ultramarathons and Ironman triathlons.

A long, hot shift looks a lot like those events. Work is hard, hours are long, and supervisors say “keep drinking.” Without a limit, a conscientious worker can drink too much. The signs are serious, so the point is worth ten seconds in a toolbox talk.

What are the signs of hyponatremia?

The review lists bloating, vomiting, nausea, headache and altered mental status as the most common symptoms in mild or moderate cases. It says nearly all symptoms are neurological. These signs overlap with heat illness, which makes field recognition hard.

A supervisor cannot sort this out at the water cooler, so do not try. Confusion, altered mental status or slurred speech is an emergency. NIOSH says to call 911 for emergency medical care when heat stroke is suspected. The same call is the right one when the cause is unclear. Learn the difference in heat exhaustion vs heat stroke and the heat illness pillar.

What should a supervisor do?

A supervisor should act on the signs, not guess the cause. Stop work for the affected worker, move them to shade, stay with them and call 911 if they are confused, vomiting repeatedly or getting worse. Do not keep pushing water on a worker who shows these signs. Let medical responders decide.

This is a supervisor’s checklist, not medical advice. Your site medical provider should approve the steps and train the crew:

1. Stop the worker’s task and move them to shade.
2. Check for confusion, slurred speech, vomiting and severe headache.
3. If any are present, call 911 and stay with the worker.
4. Tell the responders how much the worker has been drinking and for how long.
5. Do not keep forcing fluids.
6. Write down what happened for your incident log.

How do you prevent it on a crew?

Give crews a pace, a ceiling and a plan for long shifts. The 2025 review calls drinking according to thirst the main and safest individual preventive strategy. The 2019 review says the primary strategy is to avoid overdrinking during exercise. NIOSH sets practical limits for work in the heat: 1 cup of water every 15 to 20 minutes for moderate work under 2 hours, and no more than 6 cups per hour.

Put these rules in your toolbox talk and your jobsite hydration plan:

• Sip on a schedule. Do not chug.
• Do not drink past the 6-cups-per-hour ceiling.
• Do not force fluids on someone who feels sick.
• Report headache, nausea, bloating or confusion right away.
• Use a buddy system so workers watch each other.

The heat toolbox talk script already includes the six-cup ceiling.

Do electrolytes help?

They help replace what sweat takes out, but they are not a license to overdrink. NIOSH says to drink sports drinks with balanced electrolytes when sweating lasts several hours. The review’s main advice is still to drink according to thirst. Treat electrolytes as one part of the plan, not a cure for overdrinking.

JMAR’s Rapid Restoration Drops are a dietary supplement. The drops replace electrolytes lost in sweat and support hydration. They are not medicine, and they do not treat any illness. Follow the label, and read electrolytes 101 and what liquid electrolyte drops are. For why water alone can fall short, JMAR’s own post is here: Why water is not enough. Compare formats in electrolytes vs water on long shifts.

Who should check with a doctor first?

Anyone with a health condition, anyone on medication that affects fluid or sodium balance, and anyone who has had low sodium before should talk to a healthcare professional about a work hydration plan. A general guide cannot set a personal limit. Your occupational health provider can.

Heat stroke is always a 911 emergency, and so is any worker who is confused. When you are not sure which problem you face, call.

What can you say about it in a toolbox talk?

Keep it short. Add three lines to your regular heat talk. They match the guidance in this guide and take less than a minute to read aloud.

“We drink on a schedule, about a cup every fifteen to twenty minutes while we work in the heat. We do not chug. More is not better.”

“If you feel sick, have a bad headache, feel bloated or get confused, tell me right away.”

“If someone is confused, I call 911. Nobody waits and nobody forces water on them.”

Put the lines in your toolbox talk rotation. Review them with new hires on day one.

What myths should supervisors drop?

Three beliefs push crews toward overdrinking. Each has a plain correction from the sources above.

Teach the rule that pairs pace and a ceiling. It protects crews from both ends of the problem: too little water and too much.

What should you ask your occupational health provider?

Bring a short list. A provider who knows your work can set limits that fit your crews. Ask the questions below and write the answers into your plan.

1. What fluid pace and ceiling fit our hardest jobs?
2. How should we adjust for workers on medications that affect fluid or sodium balance?
3. Which signs should trigger a 911 call on our sites?
4. What first aid steps should supervisors learn?
5. How should we log fluid use during heat events?

Keep their answers with your written heat plan and review them every season.

What should you record after an incident?

Write down what happened while memories are fresh. Good notes help medical staff and help you fix the plan. Include the time, the heat reading, the worker’s task, how long they had worked and roughly how much they drank.

Add the signs you saw, who called 911, when help arrived and what you changed afterward. Share the notes with your safety lead and your occupational health provider. Do not guess at causes in the log. Record facts and let clinicians decide.

Next step

Want a hydration plan with a clear pace and ceiling for your crews? Book a 15-minute demo, ask for a free sample or see hydration programs. Related: acclimatization and sodium.