Hydration Isn't Just Water: What Really Helps for Long COVID
Plus: How do Gatorade, Pedialyte, and Liquid IV Compare
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Long Covid, MD Podcast Episode #54. Click PLAY to listen.
Last week on Long Covid, MD, we covered ways I use IV hydration to treat a long COVID flare. Today, I want to break down the science behind plain water, salt water, and oral rehydration solutions (ORS)—from the World Health Organization’s formulation to Gatorade—and explain how to use each of them to maintain your baseline health, before an exertion, and during a flare.
A disabling condition
Living with COVID-related dysautonomia can feel like a personal Squid Game, where simply standing becomes an exhausting test of survival. One evening, mid-conversation with my husband, I felt sudden light-headedness and a wave of impending doom. “Hold on,” I said, before sinking to the floor and resting my head on the bath mat. For twenty minutes I stared at the floorboards, willing myself not to pass out, while my steady but frightened husband stayed beside me. “Are you ok?!” he asked. “I don’t know…but this is fascinating,” I replied.
Since that dissociative event (the brain does what it can to deal with fear), I’ve learned a lot about dysautonomia; unfortunately, it wasn’t a focus of my medical training. I’ve learned that some of the most effective non-drug treatments are simple: water and salt.
But not all fluids work the same way.
Why fluids matter in dysautonomia
As we covered in the IV hydration post, our blood is actually composed of blood cells (like oxygen-carrying red blood cells), and plasma, which is the liquid part of blood. Plasma is the portion we can expand with fluid.
When standing, gravity pulls blood into the lower body, leaving less available to supply the brain. Typically, the autonomic nervous system responds to the drop in blood volume by constricting blood vessels to increase blood pressure.
That mechanism is disrupted in a condition like dysautonomia. To compensate, we can increase total blood volume with IV or oral fluid. If we increase blood volume enough, hopefully whatever remains when we stand is enough to reach the brain.
Drinking fluid expands plasma for variable lengths of time:
Plain water can help briefly, through a reflex that raises blood pressure.
Salt water helps the body hold onto fluid. (The steroid fludrocortisone, also called fluorinef, works this way, too.)
ORS (salt + glucose + water) supercharge absorption of water, keeping more fluid in the bloodstream.
The goal isn’t just “hydration” in the general sense—it’s strategic plasma expansion: increasing the blood volume available to circulate when upright.
Plain water: quick boost, short effect
A glass of plain water can be surprisingly powerful when used the right way. Drinking 300–500 mL rapidly (about 1-2 cups) can trigger the osmopressor reflex. This reflex increases sympathetic activity, raising blood pressure and reducing lightheadedness (Jordan, Circulation, 2000).
When to use it: before a shower, going outside in the heat, or standing for a long errand.
Limitation: the effect lasts only 30–60 minutes.
Salt water and ORS: holding onto volume
Adding salt to water extends hydration. Plain water is often lost quickly in urine, but adding salt (sodium) prevents our kidneys from excreting that water. Sodium is the main electrolyte of our body, and water follows sodium. Water wants to stick with sodium, and sodium likes to live in plasma.
The bottom line is, water expands our blood; salt keeps it expanded.
How much water and salt is best?
Guideline-based recommendations for POTS are below. Oral rehydration solutions can help us reach these goals.
Fluids: about 3 liters/day
Salt: about 10 g/day of NaCl (≈ 4 g sodium, ≈ 170 mmol)
When to use it: spread through the day with food or in drinks.
(Sheldon, et al, Heart Rhythm 2017; Managing POTS Symptoms, Standing Up to POTS)
The right salt:sugar ratio boosts hydration
Water Follows Sodium
When you drink a salty solution, sodium enters the cells lining your intestines. Water naturally follows sodium, because water always moves toward where there are more dissolved particles: this is called osmosis. The more sodium absorbed into the bloodstream, the more water comes with it — and the more your blood volume expands. This is why salty drinks or salt tablets keeps more fluid in circulation compared to plain water, which is quickly lost in urine.
The Sodium–Glucose Transporter
Your gut also has a special “pump” called the sodium–glucose transporter (SGLT1). It’s like a revolving door that only turns if both sodium and glucose walk through together. When glucose and sodium are present in the small intestine, this transporter pulls in both at the same time. Water then follows behind them into the bloodstream, more effectively than osmosis could alone.
Oral rehydration solutions (ORS), like St Mark’s and WHO formulations, are designed around this principle. They have a balanced 1:1 ratio of sodium and glucose so the transporter works at its best.
Drinks with more sugar (like some sports drinks or Liquid I.V.) throw off this balance. They may cause water to stay in the gut or even pull water into the gut, leading to bloating or diarrhea instead of raising blood volume.
Water travels between cells through osmosis, following sodium. Water travels more effectively when coupled to the Sodium:Glucose Transporter (SGLT1).
The Difference
Sodium alone: Absorbs water by osmosis. Helps retain water in the blood, but absorption is slower.
Sodium + glucose together (SGLT1): Works like a turbo-boost for absorption. Pulls sodium and water into the bloodstream faster and more efficiently, expanding blood volume more than sodium alone.
✅ Key takeaway: Water follows sodium into the bloodstream. When glucose joins sodium, absorption is even stronger. This is why oral rehydration solutions (ORS) with the right balance of sodium and glucose are more effective for plasma expansion than plain water or sugary sports drinks.
Oral rehydration solutions vary
Different ORS recipes were designed for different needs, but primarily for dehydration due to gastrointestinal loss. They mainly differ in how salty they are (salinity), how concentrated they are (osmolarity), and which electrolytes they contain.
-St. Mark’s Solution
Origin: Developed in the UK (St. Mark’s Hospital) for patients with short bowel syndrome and severe salt/fluid loss.
Sodium: 90 mmol/L (high, matches intestinal sodium loss).
Glucose: 20 g/L (90 mmol/L).
Potassium: ~20 mmol/L.
Osmolality: ~300 mOsm/L.
Intended use: Maximum sodium retention. Designed for patients who need to expand blood volume or prevent dehydration from gut disease.
Relevance for POTS/dysautonomia: Very effective because sodium content is high enough to increase plasma volume.
Where to find: Not commercially available in the US. Found in UK supermarkets, drug stores, or by prescription. You can mix it at home by following the linked recipe.
📖 Recipe: St. Mark’s Hospital Patient Leaflet PDF
-World Health Organization’s ORS
Origin: Designed for rehydration in cholera and diarrheal illness worldwide.
Sodium: 75 mmol/L (slightly lower than St. Mark’s).
Glucose: 75 mmol/L (13.5 g/L).
Potassium: 20 mmol/L.
Citrate: 10 mmol/L (alkalinizing).
Osmolality: ~245 mOsm/L.
Intended use: Balanced formula to prevent dehydration and electrolyte loss during diarrhea.
Relevance for POTS/dysautonomia: Effectively reduces POTS symptoms, supported by research.
Where to find: Readily available in the US, under various brand names, as a powder or tablet to dissolve into water. I’ve used this one called Trioral.
📖 Reference: WHO ORS Composition, Medow, 2017
-Pedialyte (commercial, U.S.)
Origin: Over-the-counter oral electrolyte solution for children with mild dehydration.
Sodium: ~45–50 mmol/L (about half of WHO or St. Mark’s).
Glucose: ~25 g/L (≈ 139 mmol/L).
Potassium: 20 mmol/L.
Osmolality: ~250–270 mOsm/L.
Intended use: Gentle hydration for mild diarrhea or vomiting.
Relevance for POTS/dysautonomia: Too low in sodium to meet the plasma-expansion target. You’d need a lot of Pedialyte to reach 170 mmol/day sodium.
Where to find: Common in US supermarkets; available on Amazon in UK
📖 Label: Pedialyte Classic Nutrition Facts
-Liquid IV and Gatorade
Like Pedialyte, these are branded electrolyte drinks that don’t contain as much sodium as the others, but if you have to choose, Pedialyte > Liquid IV > Gatorade. Remember that medical ORS have a sodium:glucose ratio close to 1:1. Pedialyte and Liquid IV have a similar ratio of about 1:3; Pedialyte is typically less expensive. Gatorade has a sodium:gluose ratio of 1:25.
⚠️ Safety caveats
Salt loading isn’t for everyone. Avoid or use with caution if you have:
Heart failure
Kidney disease
Uncontrolled hypertension
Tendency to edema
Ask your doctor if it’s safe for you to increase your salt intake.
✅ Summary
Different types of hydration:
Water bolus: short-lived boost
Salt water: daily retention
ORS: optimal absorption, sometimes equivalent to IV saline.
St. Mark’s → strongest option for POTS (most sodium)
WHO ORS → almost as good, widely available, evidence-based
Branded hydration drinks → not as much sodium; more glucose, sweeter taste
For those of us with dysautonomia, hydration is critical. Getting the right balance can be transformative for symptoms, giving you more stable upright time and better energy to live your life.
Below is a reference sheet summarizing today’s post for paid subscribers. It’s got key take-aways, an easy-to-use chart comparing the different ORS formulations, the recipe for St Mark’s rehydration solution, and linked resources. Consider upgrading for access.
👉 Have you tried ORS like St. Mark’s or WHO solution? What differences have you noticed compared with plain water or sports drinks? Share in the comments—I’d love to hear your experiences.
