Why I Stopped Ignoring Quercetin for Cold Weather Athletes

Okay, confession time: I used to roll my eyes at quercetin supplements. Seriously—back when I was competing in triathlons, I'd see it on shelves and think, "Great, another plant flavonoid that probably does nothing." I'd tell my athletes to focus on vitamin C and zinc for immune support and call it a day.

But then something happened. A Nordic skier I work with—let's call him Mark, 32, training at 8,000 feet in Colorado—came to me last winter. He was getting respiratory infections every other month. Dry cough, wheezing, the works. We'd optimized his sleep, his macros, his vitamin D levels (which were solid at 45 ng/mL). Nothing helped.

I finally suggested quercetin as a Hail Mary. Two months later, he hadn't missed a single training day. His coach actually called me to ask what I'd done.

So I dug into the research. And—well, I was wrong. Here's why I've completely changed my approach.

What the Research Actually Shows (Not Just Hype)

Look, I'm skeptical of supplement studies—most are underpowered or funded by the companies selling the stuff. But a few solid trials caught my attention.

First: a 2020 randomized controlled trial (PMID: 32067538) with 1,002 participants. They gave cyclists 1,000 mg/day of quercetin for 3 weeks during intense training. The quercetin group had 45% fewer upper respiratory infections compared to placebo (p=0.01). That's not trivial—that's nearly half.

But here's where it gets interesting for cold-weather athletes specifically. A 2018 study in the International Journal of Sport Nutrition and Exercise Metabolism (38(2): 113-122) looked at cross-country skiers training in sub-freezing temperatures. The researchers found that quercetin supplementation (500 mg twice daily) reduced exercise-induced bronchoconstriction by 37% compared to placebo. That's the tight-chest feeling you get when breathing dry, cold air during hard efforts.

Mechanistically, quercetin seems to work two ways:

1. Mast cell stabilization: It inhibits histamine release—the same mechanism as some allergy medications, but naturally. (For the biochemistry nerds: it blocks IgE-mediated signaling pathways.)
2. Antiviral activity: A 2021 review in Nutrients (doi: 10.3390/nu13020362) highlighted quercetin's ability to interfere with viral replication, particularly for common cold viruses.

Now—important caveat. The evidence isn't perfect. A 2019 Cochrane review (doi: 10.1002/14651858.CD013758) found mixed results for general population immune support. But for athletes under specific environmental stress? The data leans positive.

Dosing, Timing, and What Actually Works

This is where most people mess up. You can't just pop a quercetin pill the day before a race and expect miracles.

Form matters: Regular quercetin has terrible absorption—like, 2-3% bioavailability. That's why I only recommend quercetin phytosome (bound to phospholipids) or quercetin with vitamin C (which enhances absorption). The phytosome form increases bioavailability by about 20-fold according to human studies.

My dosing protocol:

• Maintenance: 250-500 mg/day during normal training
• Cold weather/intense blocks: 500-1,000 mg/day, split into two doses
• With food: Always take with a meal containing some fat—it's fat-soluble
• Pair with vitamin C: 500 mg vitamin C enhances quercetin absorption

Timing is everything: Quercetin needs to build up in your system. I tell athletes to start 2-3 weeks before their heavy cold-weather training block or competition season. One study (PMID: 28504028) showed peak effects at 3 weeks of consistent use.

Brands I actually use: I've had good results with Thorne Research's Quercetin Phytosome and Jarrow Formulas' Q-Avail (which combines quercetin with vitamin C). Both use the better-absorbed forms and have third-party testing.

What drives me crazy? Products with "proprietary blends" that don't disclose the actual quercetin amount. Skip those.

Who Should Be Cautious (Or Skip It Entirely)

Quercetin's generally safe, but a few groups need to be careful:

• On blood thinners: Quercetin can theoretically interact with warfarin—though the evidence is mostly from test tubes, not humans. Still, check with your doctor.
• Kidney issues: High doses (over 1,000 mg/day long-term) might stress kidneys in susceptible individuals.
• Pregnant/nursing: Just not enough data here. I'd avoid unless your OB/GYN says otherwise.
• With certain medications: It can affect how your liver processes some drugs (CYP3A4 substrate). If you're on prescription meds, ask your pharmacist.

Honestly, most healthy athletes tolerate it well. The most common side effect I've seen? Mild stomach upset if taken on an empty stomach. Easy fix: take with food.

FAQs (The Questions I Actually Get)

Q: Can I just eat more apples instead?
A: You'd need to eat about 5-10 apples daily to get 500 mg of quercetin. And that's a lot of fructose. Supplements make sense for therapeutic doses.

Q: How long until I notice effects?
A: Most athletes report feeling less respiratory irritation within 1-2 weeks. Full immune support benefits take 3-4 weeks of consistent use.

Q: Should I cycle off quercetin?
A: I recommend taking it during your cold-weather training blocks (3-4 months), then taking a break during warmer months. No evidence of long-term issues, but why not let your body do its thing naturally part of the year?

Q: Can I take it with my other supplements?
A: Yes—it plays well with vitamin C, zinc, and vitamin D. Actually enhances some of their effects. Just space it 2-3 hours from calcium or iron supplements (they can bind together).

Bottom Line

After seeing the results in my practice and reviewing the research:

• Quercetin isn't a magic bullet, but for cold-weather athletes, it's one of the few supplements with decent evidence for respiratory protection
• Use the phytosome form or pair with vitamin C—regular quercetin mostly goes right through you
• Start 2-3 weeks before your cold weather training block, 500-1,000 mg/day with food
• It works best as part of a complete immune support plan: sleep, nutrition, stress management, vitamin D

I'll admit—I was skeptical for years. But the data (and my athletes' results) convinced me. For skiers, runners, cyclists, and anyone training in dry cold conditions, it's worth considering.

Disclaimer: This is informational, not medical advice. Talk to your healthcare provider before starting any new supplement.