Immunity

1. Immunitywell supported · human dataAdded 8 October 2026

   Immunity supplements do almost nothing to stop respiratory infections

   A pooled analysis of 115 studies covering 199,055 healthy people found that nutrient supplements had little to no effect on preventing viral respiratory tract infections. The only signals were narrow: zinc appeared protective for children in Asia, and vitamin D modestly reduced infections in adults, mainly in North America.

   ⚠What it shows: As strong as this kind of evidence gets: results pooled from 115 studies covering 199,055 people in 37 countries, though the vast majority were children. The two positive signals, zinc and vitamin D, were regional and the studies behind them disagreed with each other, so even those deserve caution.Meta-analysis · Allergy

   Full breakdown →Vitamin D explained →Nutrient supplementation for prevention of viral respiratory tract infections in healthy subjects: A systematic review and meta-analysis. Allergy 2022
2. Immunitywell supported · human dataAdded 5 October 2026

   Probiotics did not stop athletes' colds, but they made them milder

   Pooled results from 14 randomised trials suggest probiotic supplements did not cut the number or length of respiratory infections in elite athletes, but they did reduce total symptom severity and lowered the inflammatory markers interleukin 6 and tumour necrosis factor alpha.

   ⚠What it shows: Reasonably solid for what it claims: results pooled from 14 trials in elite athletes, so the benefit may not carry over to everyday exercisers. The right strain, dose and timing are still unknown.Meta-analysis · J Athl Train

   Full breakdown →Probiotics explained →Probiotic Supplementation and Respiratory Infection and Immune Function in Athletes: Systematic Review and Meta-Analysis of Randomized Controlled Trials. J Athl Train 2021
3. Immunitywell supported · human dataAdded 1 October 2026

   Probiotics did nothing to ward off COVID in five trials

   Across five randomised trials, probiotic, prebiotic and synbiotic supplements showed no prophylactic effect against COVID-19: infection rates and antibody levels were no different from placebo over one to three months.

   ⚠What it shows: A consistent null across five trials spanning exposed staff, care home residents, healthy adults and household contacts, which makes it reasonably trustworthy. The trials only ran one to three months, so longer use and other infections were never tested.Systematic review · Clin Med Res

   Full breakdown →Probiotics explained →Assessment of the Prophylactic Effects of Probiotics, Prebiotics, and Synbiotics Against COVID-19 Infection: A Systematic Review of Randomized Controlled Trials. Clin Med Res 2024
4. Immunitywell supported · human dataAdded 29 September 2026

   Vitamin pills mostly flopped against COVID, with two narrow exceptions

   Across 37 randomised trials, vitamin supplements showed no consistent benefit for preventing or managing COVID-19 or long COVID. The exceptions were on death rates, where vitamin C showed a benefit and vitamin D did too, but only when given regularly.

   ⚠What it shows: The headline null is fairly firm: 37 trials where people were assigned vitamins or a comparison at random were pooled, and most outcomes showed no clear benefit from any vitamin. The two positive signals on deaths came from trials that varied widely in doses and patients, so even the authors treat them cautiously and call for better-designed studies.Meta-analysis · Nutrients

   Full breakdown →All-cause mortality explained →The Efficacy of Multivitamin, Vitamin A, Vitamin B, Vitamin C, and Vitamin D Supplements in the Prevention and Management of COVID-19 and Long-COVID: An Updated Systematic Review and Meta-Analysis of Randomized Clinical Trials. Nutrients 2024
5. Immunitywell supported · human dataAdded 27 September 2026

   Flu antivirals ranked: zanamivir speeds relief, baloxavir cuts complications

   An analysis pooling 26 randomised trials in 11,897 healthy adults and children found all four flu antivirals assessed were associated with shorter symptoms, with zanamivir linked to the fastest relief and baloxavir to the lowest risk of complications and side effects. Oseltamivir at 75 mg was the exception on tolerability, associated with more nausea and vomiting.

   ⚠What it shows: A strong basis for comparing the drugs against each other: results pooled from 26 trials in 11,897 otherwise healthy adults and children. It ranks the pills rather than telling you whether any is worth taking for a mild bout, and the complications finding rests on moderate quality evidence.Meta-analysis · JAMA Netw Open

   Full breakdown →Comparison of Antiviral Agents for Seasonal Influenza Outcomes in Healthy Adults and Children: A Systematic Review and Network Meta-analysis. JAMA Netw Open 2021
6. Immunitywell supported · human dataAdded 24 September 2026

   Vitamin D protects against respiratory infections, but only in steady doses

   Vitamin D supplementation reduced the risk of acute respiratory infections in pooled individual data from 25 trials covering 11,321 people. The protection appeared only with daily or weekly dosing, not with large bolus doses, and was strongest in people who started out severely deficient.

   ⚠What it shows: About as solid as supplement evidence gets: individual records pooled from 25 trials in 11,321 people aged 0 to 95, and the evidence was rated high quality. The catch is that the benefit vanished with occasional large-dose regimens and was concentrated in people who were deficient to begin with.Meta-analysis · Health Technol Assess

   Full breakdown →Vitamin D explained →Vitamin D supplementation to prevent acute respiratory infections: individual participant data meta-analysis. Health Technol Assess 2019
7. Immunitypreliminary · human dataAdded 18 September 2026

   Tai Chi cools inflammatory markers, but only a high dose moves all three

   Pooled results from nine randomised trials in 571 people suggest Tai Chi lowers the inflammatory marker TNF-alpha, and that IL-6 and CRP also fall when the amount of practice is high. Low amounts of Tai Chi showed little effect on IL-6 and CRP.

   ⚠What it shows: An early signal, not a verdict: results pooled from nine trials totalling 571 people, which the authors rate as relatively low quality with findings that disagreed with each other. The suggestion it could help in COVID-19 goes well beyond what these trials tested.Meta-analysis · Ann Palliat Med

   Full breakdown →Inflammation explained →Impact of Tai Chi on CRP, TNF-alpha and IL-6 in inflammation: a systematic review and meta-analysis. Ann Palliat Med 2021
8. Immunitypreliminary · human dataAdded 16 September 2026

   Probiotics may cut your odds of catching COVID and speed a mild case's exit

   A sweep of nine studies in 1,235 outpatients found probiotic use was linked to a lower chance of developing COVID-19 after exposure and faster recovery from mild infection, with fewer whole-body symptoms. Older people and those with conditions such as metabolic disorders appeared to benefit most.

   ⚠What it shows: Promising rather than proven: a sweep of eight randomised trials plus one before-and-after study in 1,235 outpatients, with the evidence rated moderate certainty overall. Only four of the nine studies were judged well run, so the size of the benefit remains uncertain.Systematic review · Nutr Health

   Full breakdown →Probiotics explained →Effectiveness of probiotics on COVID-19 prevention and treatment against mild COVID-19 in outpatient care: A systematic review. Nutr Health 2026
9. Immunitypreliminary · human dataAdded 14 September 2026

   Probiotics may give over-60s a stronger flu jab response

   Pooling ten randomised controlled trials in 1,560 adults aged 60 and over, oral lactobacilli-based probiotics increased seroconversion rates to all three strains of the seasonal influenza vaccine compared with placebo, though the reviewers caution that further research is needed to be more certain.

   ⚠What it shows: Encouraging but not settled: ten trials in 1,560 people aged 60 and over pointed the same way, but several had enough missing data to raise bias concerns, and the authors themselves call for more research before anyone leans on this.Meta-analysis · Age Ageing

   Full breakdown →Probiotics explained →The effect of oral probiotics on response to vaccination in older adults: a systematic review of randomised controlled trials. Age Ageing 2024
10. Immunitypreliminary · human dataAdded 12 September 2026

    Vitamin D's immune reputation rests on just 13 trials

    A systematic review found only 13 randomised trials of vitamin D for treating or preventing infections in humans, with the strongest signals pointing to tuberculosis, influenza and viral colds. Serious side effects from supplementation were rare, but the reviewers concluded the evidence justified further research rather than changes to care.

    ⚠What it shows: A state of the field rather than a verdict: a sweep of all the trials on this up to 2009 turned up just 13, and they differed so much in doses and patients that no firm conclusion was possible. Serious side effects were rare across the lot.Systematic review · Endocr Pract

    Full breakdown →Vitamin D explained →Vitamin D for treatment and prevention of infectious diseases: a systematic review of randomized controlled trials. Endocr Pract 2009
11. Immunitypreliminary · human dataAdded 11 September 2026

    Probiotics keep hinting at protection from UTIs, but the proof stays thin

    In a sweep of 12 recent randomised trials, probiotics showed a consistent direction of benefit for recurrent urinary tract infections, Helicobacter pylori eradication and respiratory infection symptoms, but the certainty of the evidence was rated low to moderate.

    ⚠What it shows: Promising direction, thin proof: a sweep of all the recent studies found only 12 small trials totalling 1200 people, with designs too varied to pool properly. The authors rate the certainty of the evidence low to moderate and say routine recommendations are not yet justified.Systematic review · Future Microbiol

    Full breakdown →Probiotics explained →A systematic review evaluating efficacy of probiotics in prevention and treatment of bacterial infections. Future Microbiol 2026
12. Immunitywell supported · human dataAdded 8 September 2026

    Vitamin D pills did not cut coughs and colds in healthy people

    Pooled results from 15 trials in 7053 previously healthy adults and children found vitamin D3 supplements did not significantly reduce respiratory tract infections; the 6% risk reduction observed was not statistically significant.

    ⚠What it shows: A serious sweep of the trial evidence, but with limits: results pooled from 15 trials in 7053 people, and the trials disagreed with each other while overall quality was low. It also could not properly test whether people who are genuinely deficient in vitamin D fare differently.Meta-analysis · PLoS One

    Full breakdown →Vitamin D explained →Effect of Vitamin D3 Supplementation on Respiratory Tract Infections in Healthy Individuals: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. PLoS One 2016
13. Immunitynot supported · human dataAdded 2 September 2026

    Vitamin D fails to fend off coughs and colds in trials of 30,263 people

    A meta-analysis of 30 randomised trials with 30,263 participants found vitamin D supplementation had no significant effect on preventing acute respiratory infections. Apparent benefits from daily and short-term dosing disappeared when only the highest quality trials were analysed, and publication bias was detected.

    ⚠What it shows: A convincing null: pooling 30 trials covering 30,263 people found no overall protection against respiratory infections, and the hints of benefit from daily dosing vanished in the best-run studies. Signs that unflattering results went unpublished weaken even those hints further.Meta-analysis · Nutrients

    Full breakdown →Vitamin D explained →Efficacy of Vitamin D Supplements in Prevention of Acute Respiratory Infection: A Meta-Analysis for Randomized Controlled Trials. Nutrients 2022
14. Immunitypreliminary · human dataAdded 29 August 2026

    The lower the vitamin D, the higher the COVID death rate

    Across one population study and seven clinical studies, lower blood vitamin D3 levels correlated with higher COVID-19 mortality, and a regression through the pooled data pointed to a theoretical zero-mortality level near 50 ng/mL. That is a correlation and an extrapolation, not proof that raising vitamin D prevents deaths.

    ⚠What it shows: Treat this as a pattern, not proof: it pools one population study and seven hospital studies where lower vitamin D went with more deaths, and following people like this cannot show that raising vitamin D would have saved anyone. The zero-deaths level at 50 ng/mL is a line extended beyond the data, never tested in a trial.Meta-analysis · Nutrients

    Full breakdown →Vitamin D explained →COVID-19 Mortality Risk Correlates Inversely with Vitamin D3 Status, and a Mortality Rate Close to Zero Could Theoretically Be Achieved at 50 ng/mL 25(OH)D3: Results of a Systematic Review and Meta-Analysis. Nutrients 2021
15. Immunitywell supported · human dataAdded 19 August 2026

    Probiotics cut the odds of catching a cold, but not how long one drags on

    In pooled trial data covering 3451 people, those taking probiotics were less likely than those on placebo to catch at least one acute upper respiratory infection, and antibiotic prescriptions for these infections fell too. How long an infection lasted once caught did not change.

    ⚠What it shows: Reasonably solid: results pooled from 10 trials in 3451 people, with side effects no worse than placebo and mostly minor stomach upsets. Some of the trials disagreed with each other and none covered older adults, so the true size of the benefit is uncertain.Meta-analysis · Cochrane Database Syst Rev

    Full breakdown →Probiotics explained →Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev 2011
16. Immunitywell supported · human dataAdded 15 August 2026

    Vitamin C won't stop your cold, unless you're running marathons

    In pooled trials covering 10,708 people from the general community, taking vitamin C daily did not prevent colds. Yet in marathon runners, skiers and soldiers under severe physical stress it roughly halved cold risk, and regular use shortened colds by 8% in adults and 14% in children.

    ⚠What it shows: Definitive for the average person: pooled trials in over ten thousand community members show vitamin C does not stop you catching colds. The halved risk applied only to 598 people under extreme exertion, and taking it once symptoms start showed no consistent effect.Meta-analysis · Cochrane Database Syst Rev

    Full breakdown →Vitamin C guide →Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev 2013
17. Immunitypreliminary · human dataAdded 6 August 2026

    A workout before your jab does not buy protection

    A Cochrane review of six randomised trials with 599 adults found that exercising shortly before an influenza vaccination was neither beneficial nor harmful, with no significant difference in outcomes between people who exercised and those who did not. The one trial reporting actual influenza cases also found no significant difference.

    ⚠What it shows: Cochrane review of six small RCTs (599 adults aged 18-80, study size 46-158), rated low quality: five of six trials had at least four unclear risk-of-bias domains, most measured biochemical rather than participant-centred outcomes, and no trial reported influenza complications.Meta-analysis · Cochrane Database Syst Rev

    Full breakdown →Exercise prior to influenza vaccination for limiting influenza incidence and its related complications in adults. Cochrane Database Syst Rev 2016

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