September through November is race season. If you’re signed up for a fall 10K, half marathon, or marathon, then right now — late August — you’re in the highest-volume weeks of your training block, probably in unpleasant heat, and probably starting to see ads for products promising to shave minutes off your finish time.
Most of those products won’t. A few inputs have reasonable evidence for endurance performance or recovery, and the ones that do share a theme: they work best when practiced during training, not debuted on race morning. So instead of a shopping list, here’s a timeline — what’s worth doing now, what’s worth testing in your peak weeks, and what the taper is for.
Before Anything Else: The Non-Negotiables
No supplement survives comparison with the basics, so let’s name them.
- Carbohydrate fueling. For efforts over roughly 75–90 minutes, taking in carbs during the run (commonly 30–60 g per hour, more for long marathons) is the most performance-relevant “supplement” that exists. It’s food, and it needs rehearsal — gut tolerance is trainable.
- Fluid and sodium. In August heat, long sessions can cost well over a liter of sweat per hour. Water alone isn’t enough for multi-hour efforts; most guidance lands around 300–600 mg of sodium per hour for long, sweaty sessions, adjusted for how salty a sweater you are. Our electrolytes guide covers the details — and why you don’t need electrolyte powder for a 30-minute easy jog.
- Sleep. Training adaptations are consolidated in recovery. A capsule cannot substitute for the hour of sleep you’re skipping to fit the run in.
If any of those three are broken, fix them before reading further. Everything below is a rounding error by comparison.
Now Through Early September: The Base You Can Still Build
Get tested before you supplement iron
Low ferritin is genuinely common in endurance runners — especially women, and especially during high-mileage blocks, thanks to menstrual losses, sweat, gut losses, and footstrike breaking down red blood cells. Fatigue and stalling paces can reflect low iron.
But this is the one item on this list where guessing is a bad idea. Iron accumulates, excess is associated with real harms, and supplementing without knowing your ferritin means flying blind. If your training has flatlined, ask a clinician for iron studies; if supplementation is warranted, they’ll set a dose. (Interesting wrinkle from the research: some trials suggest every-other-day iron dosing may absorb better than daily.) Don’t start iron on your own — this is a “test, don’t guess” nutrient.
Creatine: yes, even for runners (probably)
Creatine’s reputation is all barbells, but 3–5 g daily is cheap, unusually well studied, and may help endurance athletes at the margins — better repeated-surge capacity, possibly better glycogen storage when loading carbs, and some interesting preliminary work on heat tolerance because it pulls water into cells. The catch: that same water shift typically adds a pound or so of body mass, which some runners feel and dislike. August is the time to find out how your body responds — not October. If you want the background, see our creatine page. Skip the loading phase; steady daily dosing gets you there in about four weeks with less GI risk.
Vitamin D: check, don’t assume
Late summer is when your vitamin D status peaks, so a low reading now is meaningfully low, and levels will only fall as training moves into darker months. Runners train outdoors, but sunscreen, early-morning miles, and northern latitudes all cut synthesis. A test in the next month gives you a clean baseline before winter; typical maintenance doses when supplementation is warranted run 1,000–2,000 IU daily with a meal containing fat.
September: Peak Weeks — Test Your Race-Day Tools
The rule for this phase: every race-day input gets at least two or three rehearsals in training.
Caffeine — the best-supported item on this list
Caffeine at roughly 3–6 mg per kg of body weight, taken 45–60 minutes before effort, has decades of consistent evidence for endurance performance. For a 70 kg runner that’s 210–420 mg — and most people do fine at the low end, with less jitteriness and stomach churn. Things to rehearse: your dose, your timing, your gut’s opinion, and whether a mid-race top-up (gels with 25–50 mg) sits well. Habitual coffee drinkers still tend to benefit, though the effect may be smaller. If you’re caffeine-sensitive, have a heart rhythm condition, or are pregnant, this one’s not for you — and note that “800 mg pre-workout” products are a genuinely bad idea for a two-plus-hour effort.
Beetroot and dietary nitrate — modest but real
Nitrate from beetroot juice or concentrate raises nitric oxide availability and has a body of controlled trials showing small improvements in time-to-exhaustion and economy — most consistently in recreational athletes; the effect tends to shrink in the highly trained. Typical protocols use 6–13 mmol of nitrate (often 1–2 concentrated beet shots) taken 2–3 hours before the session, sometimes stacked daily for several days before a key effort. Fair warnings: it can turn urine pink (harmless, alarming) and doesn’t agree with every stomach. Details on our beetroot page. Skip antibacterial mouthwash around dosing — oral bacteria are part of how nitrate converts.
Beta-alanine — only for the shorter, harder races
For efforts in the 1–10 minute high-intensity range (and arguably for a hard 5K/10K finishing kick), beta-alanine at 3.2–6.4 g daily, split into smaller doses, builds muscle carnosine over 3–4 weeks. For a marathoner it’s likely irrelevant. The paresthesia (harmless skin tingling) is dose-dependent — another reason to split doses and start now rather than later.
Late September Into October: Taper and Race Week
The “nothing new” rule
The taper is for absorbing training, not experimenting. Whatever your race-day plan is by two weeks out — caffeine dose, fueling schedule, electrolyte plan — freeze it.
Tart cherry: the one exception worth knowing about
Tart cherry is interesting precisely because the studied protocols start before the hard effort: typically 8–12 oz of juice twice daily, or ~480 mg of extract, for 4–7 days leading into and a couple of days after a marathon or hard block. Trials have reported less soreness and faster strength recovery; the evidence is preliminary, studies are small, and the juice carries real sugar and calories. One honest caveat that applies across the board: blunting inflammation around every training session may dampen the very adaptations you’re training for — which is why antioxidant-style recovery aids make more sense around races than year-round. (The same logic shows up in the antioxidant–exercise research.) Reserve it for the race, not the whole block.
What to skip entirely
- “Endurance blends” and proprietary pre-workouts — underdosed actives, overdosed caffeine, undisclosed amounts.
- BCAAs — if you’re eating adequate protein, they add nothing meaningful.
- New anti-inflammatories on race day — NSAIDs plus dehydration plus a marathon is a combination with real kidney and gut risks; talk to a clinician rather than following forum advice.
Bottom Line
Fuel, fluids, sodium, and sleep decide most of your race. Behind them: caffeine (3–6 mg/kg, rehearsed) is the best-supported ergogenic; nitrate and creatine offer modest, plausible margins worth testing now; tart cherry is a reasonable race-week experiment; iron only ever follows a blood test. Lock everything by two weeks out, and let the taper do its quiet work. For the wider picture, our marathon runner’s guide goes deeper on the full list.
This article is educational, not medical advice. Talk with a healthcare provider before starting any supplement — especially if you’re pregnant or nursing, take medication, or are managing a health condition.