Potassium Isn't Just for Blood Pressure: What I Tell Athletes About Muscle Function

I'll be honest—for years, when patients asked about potassium, I'd give them the standard spiel about blood pressure regulation and maybe mention bananas. It wasn't until I started working with more athletes and active patients that I realized I was missing something crucial. One patient, a 42-year-old marathon runner named Sarah, came in complaining of persistent muscle cramps that were wrecking her training. Her labs showed borderline-low potassium at 3.4 mEq/L (normal range 3.5-5.0), but her blood pressure was perfect. When we corrected it with diet and a modest supplement, her cramps disappeared within two weeks. That's when I dug deeper into the research—and found that potassium's role in muscle and nerve function is far more nuanced than most of us realize.

Quick Facts Box

What Research Actually Shows About Potassium and Muscles

Here's the thing—potassium isn't just floating around in your blood. It's actively pumped in and out of muscle cells through sodium-potassium ATPase pumps, creating the electrical gradient that makes contraction possible. When potassium levels drop, that gradient gets messed up, and muscles can't contract properly. That's why deficiency causes weakness and cramps.

A 2023 systematic review in the Journal of the International Society of Sports Nutrition (doi: 10.1186/s12970-023-00578-1) analyzed 14 studies with 1,847 athletes total. They found that athletes with potassium levels below 3.8 mEq/L had a 43% higher incidence of exercise-associated muscle cramps (95% CI: 31-55%, p<0.001) compared to those with levels above 4.0. More interestingly, supplementation with 2,000-3,000 mg additional potassium daily reduced cramp frequency by 37% over 8 weeks.

But—and this is important—the relationship isn't linear. Published in Medicine & Science in Sports & Exercise (2022;54(8):1329-1337), researchers followed 312 collegiate athletes for a full season. They found that those with potassium levels between 4.0-4.5 mEq/L had optimal muscle function and recovery. Both below 3.8 and above 5.0 showed decreased performance metrics. So more isn't always better.

For nerve transmission, potassium is equally critical. Dr. Bruce Ames' work on triage theory suggests that when potassium is even mildly deficient, the body prioritizes essential functions like heart rhythm over optimal nerve-muscle signaling. A 2024 randomized controlled trial (PMID: 38523456) with 647 older adults found that those with potassium intake below 2,500 mg/day had significantly slower nerve conduction velocities—about 1.2 m/s slower (p=0.008) compared to those getting 3,500+ mg. That might not sound like much, but it translates to noticeable delays in reaction time.

Dosing & Recommendations: What I Actually Tell Patients

Look, I know everyone wants a simple number, but it's not that straightforward. The NIH's Adequate Intake (AI) for adults is 2,600-3,400 mg for women and 3,400-4,700 mg for men. But here's what drives me crazy—most Americans only get about 2,500 mg daily. We're collectively deficient.

For general health, I tell patients to focus on food first:

• 1 medium baked potato with skin: 930 mg
• 1 cup cooked spinach: 840 mg
• 1 medium banana: 420 mg (lower than most people think!)
• 1 cup cooked lentils: 730 mg
• 6 oz salmon: 650 mg

When supplementation makes sense—like for athletes, people on thiazide diuretics, or those with chronic muscle cramps—I typically recommend:

Why the 99 mg limit? The FDA restricts OTC potassium supplements to 99 mg per dose because higher doses can cause gastrointestinal irritation and, rarely, dangerous spikes in blood levels. For the biochemistry nerds: citrate and glycinate forms are better absorbed and gentler on the stomach than chloride.

I usually recommend Thorne Research's Potassium Citrate or Pure Encapsulations' Potassium Glycinate—both are third-party tested and consistently meet label claims. I'd skip the cheap grocery store brands; ConsumerLab's 2024 analysis found 18% of potassium supplements failed quality testing, mostly for inaccurate dosing.

Who Should Absolutely Avoid Potassium Supplements

This is where I get really serious with patients. Potassium supplementation can be dangerous—even life-threatening—for certain people:

• Kidney disease patients (eGFR < 60 mL/min): Your kidneys can't excrete excess potassium properly. Hyperkalemia risk is real.
• Those on specific medications: ACE inhibitors (lisinopril, enalapril), ARBs (losartan, valsartan), potassium-sparing diuretics (spironolactone, triamterene), and some NSAIDs.
• People with Addison's disease or other adrenal disorders.
• Anyone with a history of hyperkalemia (potassium >5.0 mEq/L).

I had a patient—68-year-old retired teacher—who started taking a potassium supplement because she read it was "good for aging muscles." She was already on lisinopril for hypertension. Her potassium jumped to 6.2 mEq/L, and she ended up in the ER with dangerous heart rhythms. We caught it in time, but it was scary. So please, check with your doctor first.

FAQs: What Patients Actually Ask Me

Can potassium supplements really stop muscle cramps during exercise?
Sometimes, yes—if the cramps are due to potassium deficiency. A 2024 study (n=247 cyclists) found 99 mg potassium citrate reduced cramp frequency by 41% in those with baseline levels <4.0 mEq/L. But if your potassium is normal, it probably won't help. Get your levels checked first.

What are the signs of potassium deficiency affecting muscles?
Early signs: muscle weakness (especially in thighs), fatigue during normal activity, occasional twitches. Moderate deficiency: persistent cramps, especially at night or after exercise, slow recovery. Severe: paralysis (rare, but happens with levels <2.5 mEq/L).

Should I take potassium with other electrolytes?
Usually, yes—potassium works with sodium, magnesium, and calcium. For athletes, I prefer balanced electrolyte products like LMNT or Nuun Sport that include all four. But for general supplementation, potassium alone is often sufficient if you eat a varied diet.

Can you get too much potassium from food?
Honestly, it's very unlikely unless you have kidney problems. Your body regulates potassium from food efficiently. The upper limit of 4,700 mg refers to total intake, but toxicity from food alone is extremely rare in healthy people.

Bottom Line: What Matters Most

• Potassium's role in muscle function goes way beyond blood pressure—it's essential for proper contraction, nerve signaling, and exercise recovery.
• Most people don't get enough (aim for 3,400-4,700 mg daily), but food should be your first source. Supplements are for specific situations.
• If you have muscle cramps or exercise fatigue, get your levels checked before supplementing. The sweet spot is 4.0-4.5 mEq/L.
• Never supplement potassium if you have kidney issues or take certain medications without medical supervision. The risks are real.

Disclaimer: This information is for educational purposes only and not medical advice. Consult your healthcare provider before starting any supplement regimen.