1. The basics — boring but essential

1.1 Vaccinations

• Flu vaccine: Annual. Not perfect, but reduces incidence, severity, and complications. CDC effectiveness summary
• COVID vaccine: Stay up to date. Still the best tool for preventing severe disease. CDC COVID vaccines

1.2 Sleep

Sleep < 6 hours/night is associated with significantly higher URTI risk. RCT data show even experimental sleep restriction increases susceptibility to rhinovirus infection. Prather 2015 (PMID 26118561)

Practical: Aim for 7–9 hours/night. Consistency matters more than occasional long sleeps.

1.3 Hygiene

• Handwashing: Soap + water for 20 seconds — after public spaces, before eating, after coughing/sneezing.
• Hand sanitizer: 60%+ alcohol when soap unavailable.
• Don't touch your face: Viruses enter via eyes, nose, mouth.
• Ventilation: Open windows when possible; HEPA filters help in shared spaces.

1.4 Exercise (but not too much)

Moderate regular exercise (30–60 min most days) is associated with lower URTI incidence. Nieman 2011 review (PMID 21618162)

Chronic overtraining or very high-intensity exercise without recovery can temporarily suppress immune function. Keep moving, but don't redline every day.

2. Supplements — what actually has evidence

2.1 Vitamin D

Meta-analyses show vitamin D supplementation reduces acute respiratory infections, especially in people who are deficient. The effect is modest but real. Martineau 2017 BMJ meta-analysis (PMID 28202713)

Dose: 800–2000 IU/day in winter, especially at high latitudes. Higher if deficient — discuss with your clinician.

2.2 Zinc (at first symptom)

Zinc lozenges started within 24 hours of symptom onset can reduce common cold duration by ~1 day. Hemilä 2017 Cochrane review (PMID 28515951)

Dose: 75–90 mg/day elemental zinc as lozenges, up to 7 days. Zinc acetate and zinc gluconate formulations tend to work better.

2.3 Probiotics

Multi-strain Lactobacillus/Bifidobacterium probiotics show modest reductions in URTI incidence and duration in meta-analyses. Cochrane review (PMID 24938696)

Dose: ≥10 billion CFU/day, multiple strains. Daily yogurt, kefir, kimchi, or a capsule.

2.4 Vitamin C

• Prevention: Regular 200 mg/day doesn't prevent colds in the general population, but may reduce duration by ~8–14%. Hemilä 2013 Cochrane (PMID 23440782)
• Treatment: 1–2 g/day at first symptom may have a slightly larger effect on duration.
• Special populations: Bigger benefits in people under extreme physical stress (marathons, military training, cold exposure).

Practical: 200–500 mg/day if your diet is weak in fruit/veg. At first symptom: 1000 mg 2–3×/day for a few days if you tolerate it.

2.5 Garlic

One well-designed RCT showed aged garlic extract reduced colds vs placebo. Other studies are mixed. Josling 2001 (PMID 11697022)

Cheap, low-risk. Eat garlic regularly — raw or cooked. Supplement quality varies.

2.6 Kiwi fruit

RCTs in older adults and young children show 2–4 kiwis/day reduced URTI severity and duration. Hunter 2012 RCT (PMID 22726918)

Whole food, high in vitamin C and other bioactives. Low-risk, easy to add.

2.7 Green tea (EGCG)

Small RCTs show green tea catechins (especially EGCG) may reduce flu incidence. Evidence is modest but promising. Yamada RCT (PMID 17906319)

2–3 cups/day of green tea, or EGCG supplements 200–400 mg/day.

2.8 Elderberry (Sambucus nigra)

Some RCTs show elderberry extract shortens flu duration if started within 48 hours of symptom onset. Product quality and standardization vary widely. Zakay-Rones 2004 RCT (PMID 15080016)

If you use it: choose a standardized extract and follow label doses at first symptom. Avoid raw or unripe elderberries — they're toxic.

3. "Immune boosters" — not well-supported for colds/flu

These may have other benefits or interesting lab data, but don't yet have strong human RCT evidence that they prevent or shorten colds/flu in otherwise healthy people.

• Echinacea: Cochrane review shows inconsistent effects; many trials are poor quality. Karsch-Völk 2014 Cochrane (PMID 24554461)
• CoQ10: One RCT in elderly hospitalized pneumonia patients — no good prevention data for ordinary URTIs in general population. Farazi 2014
• Chaga: Animal/in vitro data and traditional use — essentially no robust human RCTs on colds/flu. Lu 2021 review
• Cordyceps: RCTs show immune parameter changes but no significant URTI incidence reduction in healthy adults. Jung 2019 RCT
• Generic multivitamins: In well-nourished adults, RCTs show little or no effect on infection incidence.
• Cranberry: Evidence is specific to UTIs, not respiratory viruses.
• Turmeric/curcumin: Interesting anti-inflammatory and antiviral actions in vitro — no convincing RCTs on colds/flu yet.

4. Cold season protocol

4.1 Baseline — all season

• Up to date on flu + COVID vaccines.
• Sleep 7–9 hours/night consistently.
• Move most days (moderate cardio + strength) — no chronic overtraining.
• Handwash + sanitizer after public spaces; avoid face-touching.
• Fruit and veg daily (aim for 5+ servings — especially vitamin C-rich foods).
• Vitamin D 800–2000 IU/day in winter if at high latitudes or deficient.
• Probiotic (multi-strain) or daily fermented foods.
• Optional: 200–500 mg vitamin C/day if diet is weak. 2–4 kiwis/day if you like them.

4.2 When you've been exposed (plane, sick kid, coughing client)

• Tight on sleep — no late-night doomscrolling.
• Hand hygiene and not touching your face.
• Ventilation — open windows, HEPA if you have one.
• Optional low-risk boosters: green tea 2–3 cups/day, garlic and kiwi at meals.

4.3 At first symptom (scratchy throat, sniffle)

• Start zinc lozenges — ~75–90 mg/day elemental zinc, up to 7 days.
• Vitamin C 500–1000 mg, 2–3×/day for a few days (if gut tolerates).
• Hypertonic saline nasal irrigation and gentle gargling.
• Optional: elderberry extract from a reputable brand, per label.
• Drop your training load 1–2 notches and prioritise sleep.
• Stay home if you can — you're contagious before and early in the symptom course.

5. When to see a doctor

• High fever lasting > 3 days or recurring after improvement.
• Shortness of breath, chest pain, confusion, or dropping oxygen saturation.
• Severe ear pain, sinus pain, or cough producing green/brown sputum with high fever (possible bacterial superinfection).
• If you're pregnant, immunocompromised, or have significant chronic disease — lower threshold to seek care.