Condition
Flu
Flu is a contagious respiratory illness caused by influenza viruses that infect the nose, throat, and lungs, bringing fever, body aches, and deep tiredness. People most often look at vitamin D and elderberry, and a meta-analysis of elderberry examined upper respiratory symptoms, while two small analyses found asthma symptoms improved with vitamin D. Still, the vitamin D evidence is limited and neither result tested flu itself, so the picture remains unsettled.
Sources: PMID 30670267; PMID 39421966; PMID 41204244
- Supplements studied
- 3
- Graded outcomes
- 1
- Trials
- 7
- People studied
- 1,916
Evidence by supplement
- Strong
- Moderate
- Limited
- Very limited
| Grade | Outcome | Effect | Size | Studies | People | Studies list |
|---|---|---|---|---|---|---|
| Asthma Symptoms Small Improvement | Improves (the measure goes down) | Small effect | 2 studies | 334 people | ||
Studies that measured asthma symptoms | ||||||
| Upper Respiratory Tract Infection Symptoms | Improves (the measure goes down) | 13 studies | 332 people | |||
Studies that measured upper respiratory tract infection symptoms
| ||||||
| Influenza Risk | Changes; see studies | 2 studies | 1,482 people | |||
Studies that measured influenza risk | ||||||
| Fever | Improves (the measure goes up) | 1 study | 334 people | |||
Studies that measured fever | ||||||
| Pneumonia Symptoms | Improves (the measure goes down) | 1 study | 334 people | |||
Studies that measured pneumonia symptoms | ||||||
| Grade | Outcome | Effect | Size | Studies | People | Studies list |
|---|---|---|---|---|---|---|
| Upper Respiratory Tract Infection Symptoms | Improves (the measure goes down) | 3 studies | 87 people | |||
Studies that measured upper respiratory tract infection symptoms
| ||||||
| Grade | Outcome | Effect | Size | Studies | People | Studies list |
|---|---|---|---|---|---|---|
| Vaccine Augmentation | Improves (the measure goes up) | 1 study | 227 people | |||
Key findings
- Asthma SymptomsImproves (the measure goes down)
The Influenza (Flu) Prevention and Supportive Care protocol
2 primary supplements · 7 supporting supplements
- Vitamin D2,000–4,000 IU daily for prevention (target 40–60 ng/mL)
- Elderberry175–600 mg elderberry extract daily; higher dose (up to 1,200 mg) during acute illness
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Studies cited
23 studies from PubMed
- Therapeutic effect of vitamin D in acute lower respiratory infection: A randomized controlled trial
- Effects of vitamin D supplements on influenza A illness during the 2009 H1N1 pandemic: a randomized controlled trial
- Vitamin D supplementation did not prevent influenza-like illness as diagnosed retrospectively by questionnaires in subjects participating in randomized clinical trials
- Preventive Effects of Vitamin D on Seasonal Influenza A in Infants: A Multicenter, Randomized, Open, Controlled Clinical Trial
- Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren
- Vitamin D supplementation for severe pneumonia--a randomized controlled trial
- Effects of vitamin D supplementation to children diagnosed with pneumonia in Kabul: a randomised controlled trial
- Double-blind randomised controlled trial of vitamin D3 supplementation for the prevention of acute respiratory infection in older adults and their carers (ViDiFlu)
- Vitamin D supplementation for the prevention of acute respiratory tract infection: a randomized, double-blinded trial among young Finnish men
- A randomized controlled trial of vitamin D3 supplementation for the prevention of symptomatic upper respiratory tract infections
- Vitamin D₃ Supplementation Reduces the Symptoms of Upper Respiratory Tract Infection during Winter Training in Vitamin D-Insufficient Taekwondo Athletes: A Randomized Controlled Trial
- Intake of 25-Hydroxyvitamin D3 Reduces Duration and Severity of Upper Respiratory Tract Infection: A Randomized, Double-Blind, Placebo-Controlled, Parallel Group Comparison Study
- Vitamin D3 and gargling for the prevention of upper respiratory tract infections: a randomized controlled trial
- Effect of vitamin D3 supplementation on upper respiratory tract infections in healthy adults: the VIDARIS randomized controlled trial
- Vitamin D supplementation and upper respiratory tract infections in adolescent swimmers: a randomized controlled trial
- Vitamin D supplementation decrease asthma exacerbations in children: a systematic review and meta-analysis of randomized controlled trials.
- Association between prenatal vitamin D supplementation and respiratory diseases in children: a systematic review and meta-analysis.
- Vitamin D Supplementation and the Risk of Colds in Patients with Asthma
- Double-blind randomised placebo-controlled trial of bolus-dose vitamin D3 supplementation in adults with asthma (ViDiAs)
- Efficacy and safety of the standardised Ginseng extract G115 for potentiating vaccination against the influenza syndrome and protection against the common cold corrected
- Black elderberry (Sambucus nigra) supplementation effectively treats upper respiratory symptoms: A meta-analysis of randomized, controlled clinical trials.
- Elderberry for prevention and treatment of viral respiratory illnesses: a systematic review.
- Elderberry Extract Outpatient Influenza Treatment for Emergency Room Patients Ages 5 and Above: a Randomized, Double-Blind, Placebo-Controlled Trial.