The supplements worth taking as a runner depend on whether you’re fixing a deficiency or chasing a performance edge. A few have strong evidence behind them: iron if your levels are low, vitamin D for bone protection, protein if your diet falls short, and caffeine before race day. Others, like beta-alanine and beetroot juice, help in narrower situations. And some popular options, like magnesium for cramps, don’t hold up under scrutiny.
Iron: The Most Common Deficiency in Runners
Iron deficiency is the single most performance-limiting nutrient gap for distance runners. The repetitive foot strike of running destroys small numbers of red blood cells with every step, and iron is also lost through sweat and the gut. Female runners, vegetarians, and high-mileage athletes are at the highest risk.
The tricky part is that you can be iron-depleted long before you become anemic. Ferritin, the storage form of iron, drops first. Research on athletes classifies ferritin below 20 ng/mL in women and below 30 ng/mL in men as iron deficiency. Some sports medicine specialists set the bar even higher, considering anything below 30 ng/mL as absolute deficiency and 30 to 99 ng/mL as functionally deficient for competitive athletes. If your easy runs feel harder than they should, your pace is slipping for no clear reason, or you’re unusually fatigued, a blood test checking ferritin (not just hemoglobin) is the right first step.
Don’t supplement iron blindly. Too much iron causes its own problems. Get tested, and if your ferritin is low, your doctor can recommend the right dose. Taking iron with vitamin C and away from coffee or tea improves absorption significantly.
Vitamin D for Bone Health and Stress Fractures
Runners load their bones with thousands of impacts per run, making stress fractures a real concern. Vitamin D plays a direct role in calcium absorption and bone remodeling, and low levels increase your fracture risk substantially. Blood levels below 40 ng/mL are strongly associated with a higher prevalence of stress fractures in athletes.
The protective target is a serum concentration of 40 ng/mL or above. Getting there typically requires supplementation, especially if you train indoors, live at a northern latitude, or have darker skin. Research on military recruits and athletes found that daily supplementation with 800 IU of vitamin D plus 2,000 mg of calcium reduced stress fracture rates. Recommendations for athletes range from 800 to 2,000 IU daily, with some protocols going up to 4,000 IU per day to reach that 40 ng/mL threshold. A simple blood test can tell you where you stand and how aggressive your supplementation needs to be.
Protein: Higher Than You Think
Most runners underestimate their protein needs. The general recommendation for sedentary adults is about 0.8 grams per kilogram of body weight per day. Endurance athletes need roughly 1.8 g/kg, which is more than double that baseline. For a 150-pound (68 kg) runner, that works out to about 122 grams of protein daily.
Whole foods should be your primary source: chicken, fish, eggs, Greek yogurt, beans, tofu. But protein powder can fill a practical gap, especially in the 30 to 60 minutes after a hard run when appetite is low and muscle repair is already underway. Whey protein is the most studied option for fast absorption post-exercise, though plant-based blends work well too. The key is hitting your daily total, not obsessing over any single meal’s timing.
Caffeine: The Best Legal Performance Booster
Caffeine is the most reliably effective ergogenic aid available to runners. It improves endurance, reduces perceived effort, and sharpens focus. The performance-enhancing dose is 3 to 6 mg per kilogram of body weight, taken about 60 minutes before exercise. For a 70 kg runner, that’s 210 to 420 mg, roughly equivalent to two to four cups of coffee.
Caffeine chewing gums absorb faster than capsules or coffee, so the timing window can be shorter with those products. If you’re a regular coffee drinker, you’ll still get a benefit, though the effect may be slightly blunted. The main caution: practice your race-day caffeine strategy during training. A dose that’s too high can cause jitteriness, a racing heart, or stomach issues mid-run.
Beetroot Juice and Nitrate Supplements
Beetroot juice works by delivering dietary nitrate, which your body converts into nitric oxide. Nitric oxide widens blood vessels and improves how efficiently your muscles use oxygen. In controlled studies, six days of supplementation with about 500 mL of beetroot juice daily (providing roughly 6.2 mmol of nitrate) reduced the oxygen cost of both walking and running. That means you use less energy at the same pace, which is the definition of better running economy.
The benefit is most noticeable in recreational and moderately trained runners. Highly elite athletes seem to respond less, likely because their bodies are already extremely efficient at oxygen delivery. If you’re running 5Ks through half marathons and looking for a small but measurable edge, concentrated beetroot shots (available at most running stores) taken for several days leading into a race are worth trying.
Beta-Alanine for Shorter, Harder Efforts
Beta-alanine increases the amount of carnosine stored in your muscles, which buffers the acid buildup that causes that burning sensation during high-intensity efforts. Four weeks of supplementation at 4 to 6 grams daily (split into doses of 2 grams or less to avoid a harmless but annoying tingling sensation) raises muscle carnosine levels by 40 to 60 percent.
The catch: the performance benefits are most pronounced for efforts lasting 1 to 4 minutes. That makes beta-alanine useful for 800-meter and mile specialists, or for the finishing kick in a 5K. If you’re primarily a half-marathon or marathon runner, the evidence is less compelling. It won’t hurt, but it’s unlikely to be the supplement that moves the needle for longer, steadier efforts.
Omega-3 Fatty Acids for Recovery
The omega-3 fats EPA and DHA help manage the inflammation that follows hard training. A systematic review of randomized controlled trials found that at least 2,400 mg per day of combined EPA and DHA, taken for a minimum of about 4.5 weeks, appears effective at reducing exercise-induced muscle damage and inflammation markers. Most of the positive studies used doses in the range of 1,500 to 3,000 mg of combined EPA/DHA.
You won’t feel a dramatic difference after a single dose. Omega-3s work by gradually shifting the balance of inflammatory compounds in your tissues over weeks. For runners in heavy training blocks or marathon cycles, consistent daily supplementation can support recovery between sessions. Check the label for the actual EPA and DHA content, not just the total fish oil amount, since many capsules contain far less active omega-3 than the front label suggests.
Electrolytes and Sodium During Long Runs
You lose sodium in your sweat, and the rate varies enormously between individuals. Measured sweat sodium concentrations in athletes range from 15 to 99 milliequivalents per liter, meaning some people lose several times more salt than others during the same workout. Standard sports drinks contain about 20 mEq/L of sodium or less, which is on the low end for heavier or saltier sweaters.
For runs under 60 to 75 minutes, water alone is fine for most people. For longer efforts, especially in heat, adding sodium through electrolyte tablets, capsules, or higher-sodium drink mixes helps maintain fluid balance and prevents the bloated, sloshy feeling that comes from drinking plain water without replacing salt. If you notice white salt stains on your clothes or hat after runs, you’re likely a salty sweater who benefits more from targeted sodium replacement.
Creatine: Probably Not for Distance Runners
Creatine is one of the most well-researched supplements in sports nutrition, but it’s built for power and strength, not endurance. The loading phase (20 grams per day for five days) typically causes 1 to 2 kg of weight gain in the first week, mostly from water retention in muscles. For a runner, that extra weight increases the energy cost of every stride. Research has noted that for propulsive, anti-gravity activities like running, the body mass gain from creatine may cancel out any performance benefit.
If you’re a sprinter or you incorporate significant strength training alongside your running, creatine may help in the gym. For distance runners focused on race performance, it’s generally not worth it.
Magnesium: Not the Cramp Fix You’ve Heard
Magnesium supplements are widely marketed to runners for preventing muscle cramps, but the evidence doesn’t support that claim. A Cochrane Review found that oral magnesium supplementation (at doses ranging from 100 to 520 mg of elemental magnesium daily) did not significantly reduce cramp frequency, intensity, or duration compared to placebo. The review concluded that magnesium is unlikely to be effective for muscle cramps at any dosage studied.
That said, magnesium plays a role in hundreds of bodily processes including sleep quality, muscle relaxation, and energy metabolism. Many runners don’t get enough from food alone. If you’re supplementing magnesium for general health or better sleep, that’s reasonable. Just don’t expect it to solve your cramping problem. Exercise-associated cramps appear to be driven more by neuromuscular fatigue than mineral deficiency.