Low sodium can cause headaches, but the kind that matters is low sodium in your blood (hyponatremia), not a low-salt diet. It often comes with nausea and a foggy feeling, and a fast drop can be dangerous. For most people, cutting back on dietary salt doesn’t bring on headaches and may even mean fewer of them.1PubMed Central. Lower Sodium Intake and Risk of Headaches: Results From the Trial of Nonpharmacologic Interventions in the Elderly The main exception is rapid salt and water loss, as happens when people start keto.
Why Low Blood Sodium Can Make Your Head Hurt
On a blood test, low blood sodium shows up as a sodium result below about 135 mmol/L. When blood sodium drops, the blood becomes more watery than the fluid inside your cells, so water flows into the cells and they swell.2PubMed Central. Hyponatremia and the Brain Headache is one of the first signs, along with nausea.3PubMed Central. Pathophysiology and treatment of exercise-associated hyponatremia The swelling can become severe, since an increase in brain volume of 8% to 10% can be fatal.4Cleveland Clinic Journal of Medicine. Neurologic effects of hyponatremia and its treatment
The skull is rigid, so swollen brain tissue has almost nowhere to go and pressure inside the head rises. That pressure stretches pain-sensitive tissue around the brain, which is why this kind of headache tends to feel diffuse and persistent rather than pinpointed. The same pressure can cause nausea and drowsiness, so these symptoms tend to travel together.
Blood sodium and the salt you eat are two different things. Your kidneys normally keep blood sodium steady even when your diet swings a lot. Low blood sodium usually comes from too much water, or from a body that holds on to water, rather than from eating too little salt. That’s why a low-salt diet alone rarely makes blood sodium fall.
A headache with confusion or vomiting points to the brain being affected, which is not what a simple tension headache looks like. A headache on its own is less likely to be from low sodium, though it can be an early sign, especially after heavy water intake or a new medicine.
Speed matters more than the number itself. The brain can slowly push out salts to shrink its cells back toward normal, but that adjustment takes time.5Cleveland Clinic Journal of Medicine. Neurologic effects of hyponatremia and its treatment So a drop over less than about 48 hours is far more likely to cause symptoms than a slow one.6PubMed Central. Effects of Hyponatremia on the Brain Even mild, slow-developing low sodium isn’t always harmless, though. It can bring headache, poor attention, unsteady walking and falls, and some of these symptoms improve once sodium returns to normal.7PubMed Central. Acute and Chronic Hyponatremia
Does Eating Less Salt Cause Headaches
Salt reduction studies don’t show a rise in headaches, and some show fewer. In a trial of older adults told to cut salt, about 10.5% had headaches compared with 14.3% who didn’t cut back.8PubMed Central. Lower Sodium Intake and Risk of Headaches: Results From the Trial of Nonpharmacologic Interventions in the Elderly Eating less salt was linked to fewer headaches regardless of blood pressure changes.9PubMed Central. Lower Sodium Intake and Risk of Headaches: Results From the Trial of Nonpharmacologic Interventions in the Elderly Another study found a lower headache risk on a low-salt diet, though most of those headaches were probably tension headaches.10PubMed Central. Severe Headache or Migraine History Is Inversely Correlated With Dietary Sodium Intake: NHANES 1999–2004 In a very large trial where people swapped regular salt for a lower-sodium salt substitute, headaches were just as common, about 27% in both groups, and no more severe.11PubMed Central. The effect of salt substitution on frequency and severity of headache: results from the SSaSS cluster-randomised controlled trial of 20,995 participants
One population study points the other way. A large U.S. survey found that people who ate more salt were less likely to report severe headache or migraine.12PubMed Central. Severe Headache or Migraine History Is Inversely Correlated With Dietary Sodium Intake: NHANES 1999–2004 But that survey included people eating far more salt than the average American, so it can’t say that cutting back causes headaches. A perspective piece also notes that some migraine sufferers report fewer headaches with more salt.13Frontiers in Nutrition. Specifically formulated ketogenic, low carbohydrate, and carnivore diets can prevent migraine: a perspective
The studies seem to disagree because they answer different questions. In a trial, people are assigned to eat less salt, so any difference in headaches between groups can be traced to the diet change. A survey only records what people already eat and report, so it can show a pattern without showing what caused it. People who get frequent headaches may skip meals or avoid certain foods, and their salt intake may differ because of appetite, nausea or overall diet quality. That is why the trial results carry more weight here.
If you’re cutting salt for blood pressure, there’s no good reason to stop a doctor-advised low-salt diet over headache worries. If headaches start, look first at other changes such as caffeine, sleep or a new medicine.
Keto Headaches and Fast Salt Loss
When you stop eating carbohydrates, insulin drops and the kidneys stop holding on to sodium and water.14Superpower. Keto Headache: Why It Happens and How to Stop It In the first few days the body also uses up its stored carbohydrate and releases the water bound to it.15Superpower. Keto Headache: Why It Happens and How to Stop It This ongoing sodium loss and slight drop in fluid can cause headache, dizziness, lightheadedness on standing, tiredness and constipation, the familiar “keto flu.”16PubMed Central. Symptoms during initiation of a ketogenic diet: a scoping review of occurrence rates, mechanisms and relief strategies This is salt and fluid loss together, a different problem from having too much water.
That difference changes the fix. Replacing some salt and fluid helps here, while drinking extra plain water would do nothing for a dilution problem. The two can overlap if someone loses salt and also drinks large amounts of plain water, so drinking to thirst is still sensible.
Symptoms often peak early and for many people fade within a week or two as the body adapts. A headache that keeps worsening or comes with confusion is not ordinary keto flu.
Adding some salt, such as broth, during the first weeks is a common way to ease keto-flu symptoms. People with high blood pressure, heart disease or kidney disease should check with a doctor before adding salt.
Headaches From Drinking Too Much Water During Exercise
Drinking more fluid than you lose during long exercise such as a marathon can dilute blood sodium. It often causes no symptoms or just mild tiredness, nausea and headache.17I Spy Physiology Blog. Marathon Runners: There’s a Downside to Drinking Too Much Water Bloating, vomiting and confusion are other common signs, nearly all caused by brain swelling.18PubMed Central. Pathophysiology and treatment of exercise-associated hyponatremia
Early signs such as nausea, headache and feeling puffy can look like dehydration or race fatigue.19Proven Science Nutrition. Hyponatremia: The Danger of Over-Hydrating The instinct to drink more water can then make things worse.20PubMed. Death from hyponatremia as a result of acute water intoxication in an Army basic trainee In one army trainee, symptoms were mistaken for dehydration, and more water led to fatal brain and lung swelling.21PubMed. Death from hyponatremia as a result of acute water intoxication in an Army basic trainee
Some clues can help tell the two apart, though none is reliable on its own. Weight gain, puffy hands or tight rings, and pale, frequent urine point to too much water. Thirst, dark urine and weight loss point to dehydration. When you’re unsure, stop drinking plain water and get medical help rather than drinking more.
On long efforts, drink to thirst rather than on a fixed heavy schedule. A set amount per hour can exceed what you’re actually losing. On events lasting several hours, use drinks or snacks that contain salt.
Weighing yourself helps too. Step on the scale before and after a long run or session, in similar clothing and with no toilet stops in between. Gaining weight suggests you drank more than you lost. Losing a small amount is expected, so a modest drop doesn’t mean you should drink more next time.
Medicines and Health Conditions That Lower Sodium
Common antidepressants such as sertraline can lower sodium, especially in older adults.22PubMed Central. Selective Serotonin Reuptake Inhibitor-Induced Hyponatremia: Clinical Implications and Therapeutic Alternatives In one older man taking sertraline with a water pill, sodium stayed low after the water pill was stopped and recovered only after the antidepressant was switched.23PubMed Central. Selective Serotonin Reuptake Inhibitor-Induced Hyponatremia: Clinical Implications and Therapeutic Alternatives Some seizure medicines can also lower sodium, with subtle signs like headache, irritability, nausea and confusion.24PubMed Central. Hyponatremia With Anticonvulsant Medications: A Narrative Review Sodium can fall quite low on these medicines before any symptoms appear.25PubMed Central. Hyponatremia With Anticonvulsant Medications: A Narrative Review
Older adults are more vulnerable. Combining several sodium-lowering drugs raises the risk, since two together, such as an antidepressant and a water pill, add to each other’s effect. People with heart, liver or kidney disease hold water more easily. Telling every prescriber what you already take helps the combination get noticed.
If you take one of these medicines, don’t stop it on your own, because stopping suddenly can cause its own problems, including withdrawal or seizures. Ask your prescriber whether a sodium blood test makes sense, especially after starting or raising a dose. A new headache with nausea or unsteadiness soon after a change is worth reporting so it can be checked.
Some illnesses make the body release too much of a water-holding hormone, which dilutes sodium. About 1 in 10 people with brain infections such as meningitis developed this problem.26PubMed. Comparison of hyponatremia and SIADH frequency in patients with tick borne encephalitis and meningitis of other origin Autoimmune disease such as lupus can rarely cause it too, presenting with a day of worsening headache, vomiting and confusion.27PubMed Central. Severe Hyponatremia From Lupus-Related Syndrome of Inappropriate Antidiuresis (SIADH): A Diagnostic Challenge Pain itself also triggers release of a water-holding hormone, so severe headaches can nudge blood sodium down rather than the reverse.
Sodium and Migraine
Brain scans found that sodium rises in the fluid around the brain and spine during migraine, but not in the blood.28Newsroom. Migraines and salt: USC neurologist connects the dots This sodium returned to normal when the same people were headache-free.29Newsroom. Migraines and salt: USC neurologist connects the dots So migraine seems to involve sodium handling inside the brain, not low blood sodium.30PubMed Central. Severe Headache Trajectory Following Aneurysmal Subarachnoid Hemorrhage: The Association with Lower Sodium Levels
The brain-scan finding shows sodium changing along with migraine, not that the change causes the attack. It may result from what happens inside the brain during a migraine rather than trigger it, and larger studies would be needed before treatments could be built on it.
For someone with migraine, the evidence doesn’t yet support adding salt as a treatment, and results on salt and migraine point both ways. Keeping a diary of salt intake and attacks gives you something concrete to discuss with a doctor before changing anything.
When a Low Sodium Headache Is an Emergency
Low sodium can progress from nausea and headache to seizures and breathing stopping within 20 minutes, especially when sodium is below 115 mmol/L.31Cleveland Clinic Journal of Medicine. Neurologic effects of hyponatremia and its treatment Headache with confusion, repeated vomiting, unusual sleepiness or a seizure needs emergency care rather than waiting to see if it passes. If someone is hard to wake or has a seizure, call emergency services rather than driving them yourself if you can.
A headache after a long event during which you drank a lot should raise concern, as should one soon after starting or raising a medicine known to lower sodium. Tell staff about water intake, exercise and medicines so they test sodium.
While waiting, don’t keep drinking plain water in the hope it helps, since if sodium is low this can worsen it. Don’t take salt tablets or large amounts of salt on your own either, because the right treatment depends on the cause and is best guided by a test. Stay with the person and note how symptoms are changing.
At the hospital, a simple blood test measures sodium within minutes. Severe cases get a concentrated salt solution, given carefully. Doctors raise sodium slowly, because correcting it too fast can also harm the brain.
When More Salt Is Actually Recommended
Some people are told to eat more salt. Extra salt improved symptoms and blood volume in people with POTS, a condition causing a racing heart on standing.32PubMed. Salt supplementation in the management of orthostatic intolerance: Vasovagal syncope and postural orthostatic tachycardia syndrome A high-salt diet also reduced the heart-rate jump on standing, though in that study overall symptoms didn’t clearly improve.33PubMed Central. Systematic literature review: treatment of postural orthostatic tachycardia syndrome (POTS) Extra salt is a doctor-guided treatment for particular conditions like this, not a general headache fix.
Extra salt can raise blood pressure in many people, so don’t self-prescribe salt tablets. If headaches come with dizziness on standing, talk to a doctor.