Does vitamin D prevent colds and infections?
Short answer
Not clearly; any effect looks small.
Early pooled trial analyses found slightly fewer respiratory infections with vitamin D. The newest and largest one, 40 trials and 61 589 people, found the difference too small to be sure it is real.
This page says what the research shows. It does not say whether you should take vitamin D.
Where the evidence stands
Each dot is one on-topic paper. Steps near the top answer the question more directly. Select a dot to see the study.
↑ Stronger evidence
-
Trials in people: colds, flu and chest infections
Trials that measured colds, flu and other respiratory infections directly.
10 -
Trials in people: other measures
Trials that measured other health or performance measures.
5 -
Trials in people: lab tests or safety
Trials that measured lab tests, side effects or safety.
1 -
Population studies
Studies that followed or surveyed groups of people. They show links, not causes.
1 -
Blood levels and genes
Studies that link blood levels or genes to health.
4
↓ Weaker evidence
- Points to benefit
- Mixed
- No difference
- No direction
- Points to harm
Not on the ladder: 8 reviews of many studies (shown below), 4 opinion or narrative papers. Counts are papers, not people. Some studies appear in more than one paper.
See every studyWhat we found
- The 2025 pooled analysis of 40 placebo trials and 61 589 people found odds of infection of 0.94 with vitamin D; the range, 0.88-1.00, includes no effect. Jolliffe 2025
- Earlier pools found slightly lower odds of infection: 0.88 across 25 trials in 2017, and 0.92 in 2021 (61.3% vs 62.3% of people infected). Martineau 2017, Jolliffe 2021
- In VITAL, 15 804 older adults took 2000 IU a day or placebo; the odds of a cold or upper respiratory infection were 0.96, meaning no clear change. Camargo 2024
- Vitamin D did not change how many people had serious side effects: odds of 0.96 in the 2025 pool and 0.97 in the 2021 pool. Jolliffe 2025, Jolliffe 2021
What the research says
Pooled trials: a small benefit that faded
The 2017 analysis of 25 trials found slightly lower odds of a respiratory infection with vitamin D (0.88). The 2021 update found 61.3% vs 62.3% of people had at least one infection (0.92). The 2025 update found 0.94, with a range reaching 1.00, so protection is no longer clear.
Each update builds on the trials of the one before, so they are not separate confirmations. The 2025 authors say the overall estimate barely moved; what changed is that its range now includes no effect.
Studies: Martineau 2017, Martineau 2019, Jolliffe 2021, Jolliffe 2025
Daily dosing and low starting levels: mixed answers
The 2017 analysis saw benefit with daily or weekly doses (0.81) but not with large single (bolus) doses (0.97). Benefit was biggest when starting blood levels were under 25 nmol/L (0.30). The 2021 update also found benefit with daily dosing (0.78).
But the 2021 update found no effect by starting level, and the 2025 update found no difference by dosing pattern, dose size or starting level. In VITAL, the 255 people starting under 12 ng/mL had odds of 0.60, but the range (.28-1.30) includes no effect.
Studies: Martineau 2017, Martineau 2019, Jolliffe 2021, Jolliffe 2025, Camargo 2024
Large adult trials mostly found no effect
VITAL gave 15 804 older adults 2000 IU a day and found no change in colds and similar infections (0.96). CORONAVIT offered a blood test, then 800 or 3200 IU a day: 5.7% and 5.0% had an infection vs 4.6% with no offer, ranges including no effect.
D-Health gave 21,315 older Australians 60,000 IU a month; hospital stays for respiratory infection did not change (0.93). In adults with asthma, colds were not less frequent (1.2). In a Chicago COVID-19 trial, higher vs low doses gave 10.9% vs 14.7%, not clearly different (P = 0.10).
Studies: Camargo 2024, Jolliffe 2022, Pham 2023, Denlinger 2016, Meltzer 2026
Children: some trials found fewer infections, others not
A 2024 guideline review rated evidence of fewer infections in children as low certainty. In Danish 6 to 8 year olds, 20 µg a day through winter gave 17% fewer sick days from infection. High-dose vitamin D in pregnancy went with less croup by age 3 (11% vs 18%).
But weekly doses did not change infection counts in Chilean toddlers (P = .85) or respiratory hospital stays in Mongolian schoolchildren over 3 years (29 vs 34 children). In Taiwan, a month of daily doses gave 84% lower flu risk, not clearly different (p = 0.055).
Studies: Shah 2024, Clerico 2025, Brustad 2023, Reyes 2024, Ganmaa 2020, Huang 2022
Once sick: trials mixed, blood-level links unproven
In older adults with COVID-19, one 400,000 IU dose gave fewer deaths at 14 days than 50,000 IU (6% vs 11%), but not at 28 days. Tunisian patients tested negative later with vitamin D (37 vs 28 days). Children in hospital with lung infections saw no benefit.
Population studies link low blood vitamin D to life-threatening RSV in babies and to COVID-19 hospital stays and deaths in veterans. These show links, not causes. A 2023 review notes genetic studies found no link, and such links may reflect other differences or illness lowering vitamin D.
Studies: Annweiler 2022, Abroug 2023, Somnath 2017, Milani 2024, Ferolla 2022, Seal 2022, Martineau 2023
What reviews of many studies found
Reviews pool or sum up earlier studies. They are not on the ladder, because they repeat studies already counted there.
Pooled review (meta-analysis) · Jolliffe 2025
Pooled 40 placebo-controlled trials with 61 589 people. Odds of a respiratory infection were 0.94 (0.88-1.00), which includes no effect. No differences by age, starting vitamin D level, dosing frequency or dose size.
Pooled review (meta-analysis) · Jolliffe 2021
Pooled 43 trials with 48 488 people. Slightly fewer people had an infection with vitamin D (61.3% vs 62.3%; 0.92). Daily dosing showed protection (0.78); starting vitamin D level made no difference.
Pooled review (meta-analysis) · Martineau 2017
Pooled individual data from 25 trials and 10 933 people. Odds of infection were 0.88 with vitamin D. Benefit came with daily or weekly doses, not bolus doses, and was largest when starting levels were under 25 nmol/L.
Pooled review (meta-analysis) · Abioye 2021
Pooled trials of vitamins and minerals in adults; the abstract gives no trial count. Vitamin D lowered infection risk slightly (0.97; 0.94 to 1.00) and shortened symptoms by 6%.
How the research grew
The papers we read span 2012 to 2026. 8 of the 33 on-topic papers came out in 2024 to 2026. The earliest trial in people here is from 2015.
- 2012
- 2015
- 2016
- 2017
- 2019
- 2020
- 2021
- 2022
- 2023
- 2024
- 2025
- 2026
Each dot is one on-topic paper, colored by what it found. Rings mark key papers:
- 2012. 2012 review links low levels to infections, urges trials. Bozzetto 2012
- 2017. 2017: individual-data pooling of 25 trials finds benefit. Martineau 2017
- 2023. Largest trial: 21,315 older Australians, no fewer admissions. Pham 2023
- 2024. VITAL: 15 804 older adults, no fewer colds. Camargo 2024
- 2025. 2025 update: protection no longer clear across 40 trials. Jolliffe 2025
Doses tested
8 trial papers gave a set daily amount in iu a day, from 800 to 10,000. Each dot shows the dose and what the trial found.
- iu a day02,0004,0006,0008,00010,00012,000
- Points to benefit
- Mixed
- No difference
- No direction
- Points to harm
One row per paper, so a trial reported in two papers appears twice.
Not shown: 8 trial papers with no single daily dose in the abstract, or a different unit.
Who funds this research
3 of 16 trial papers report a company stake: Pharmavite (VITAL), Mylan (COVIT-TRIAL) and vitamin D makers such as Pharma Nord and DSM (CORONAVIT). Two of the three found no effect; 7 trials lack PubMed disclosures. Stakes did not change the confidence.
- Company stake 3
- No disclosure in PubMed 7
- No stake declared 6
- Camargo 2024Company stake
- Annweiler 2022Company stake
- Jolliffe 2022Company stake
- Brustad 2023No disclosure in PubMed
- Mayan 2015No disclosure in PubMed
- Pham 2023No disclosure in PubMed
- Grant 2016No disclosure in PubMed
- Denlinger 2016No disclosure in PubMed
- Golan-Tripto 2020No disclosure in PubMed
- Somnath 2017No disclosure in PubMed
- Ganmaa 2020No stake declared
- Clerico 2025No stake declared
- Huang 2022No stake declared
- Abroug 2023No stake declared
- Reyes 2024No stake declared
- Meltzer 2026No stake declared
Funding rule. A stake is always shown. Confidence is lowered only when every supporting study comes from a party with a stake. "No disclosure in PubMed" means the PubMed record has no conflict-of-interest statement. It does not mean there is no conflict.
All 33 on-topic papers
Each paper shows what it tested, what it found, and who has a stake. Every paper also has its own page that explains how much it counts and how it fits. See every study as a list.
-
Randomized trial · measured the question itselfMeltzer et al., 2026Clinical nutrition (Edinburgh, Scotland) · PubMed
Effect of moderate or high versus low dose daily vitamin D on COVID-19 incidence: A double-blind, parallel-group randomized clinical trial.
923 people · Adults in Chicago who chose a moderate-vs-low or high-vs-low dose branch
Tested4000 or 10,000 IU of vitamin D a day vs 400 IU a day, for up to 9 months
COVID-19 in 10.9% (50/461) on moderate or high dose vs 14.7% (68/462) on low dose (aHR:0.73; 95%-CI:0.51-1.06; P = 0.10). Moderate vs low: aHR:0.62 (0.39-0.99). High vs low: aHR:0.99 (0.53-1.86).
No differenceNo stake declaredAbstract onlyNo competing interests declared; funded by an NIH institute.
-
Randomized trial · measured the question itselfClerico et al., 2025European journal of nutrition · PubMed
Effects of vitamin D supplementation on acute respiratory tract infections in 6-8-year-old children: a randomized clinical trial.
189 people · Healthy 6 to 8 year old children in Copenhagen, Denmark
Tested20 µg of vitamin D3 a day vs placebo for 24 winter weeks
Children on vitamin D had 17% fewer sick days from respiratory infection (risk ratio, 0.83; 95% CI, 0.76-0.90) and 43% fewer days with infection and fever (RR, 0.57; 95% CI, 0.48-0.67).
Points to benefitNo stake declaredAbstract onlyNo conflict of interest stated by the authors.
-
Randomized trial · measured the question itselfCamargo et al., 2024Clinical infectious diseases : an official publication of the Infectious Diseases Society of America · PubMed
Effect of Daily Vitamin D Supplementation on Risk of Upper Respiratory Infection in Older Adults: A Randomized Controlled Trial.
15,804 people · Mostly healthy men aged 50+ and women aged 55+, average age 68
TestedVitamin D3 2000 IU a day vs placebo, with a check at 1 year
Vitamin D did not change the odds of a recent cold or upper respiratory infection (OR 0.96, 95% CI .86-1.06). In the 255 people with low levels (<12 ng/mL), OR was 0.60 (.28-1.30).
No differenceCompany stakeAbstract onlyPharmavite supplied the vitamin D pills and supported the trial; some authors report ties to Pharmavite, Pfizer and Quest Diagnostics.
-
Weekly Vitamin D Supplementation to Prevent Acute Respiratory Infections in Young Children at Different Latitudes: A Randomized Controlled Trial.
303 people · Chilean children aged 1.5 to 3.5 years in three cities
TestedVitamin D3 at 5600 or 11,200 IU a week vs placebo for 6 months
No group differences in number of respiratory infections (P = .85) or infection hospital stays (P = .20). Blood vitamin D rose with dose; 64% completed the study.
No differenceNo stake declaredAbstract onlyNo conflicts of interest declared; funded by a national Chilean health research fund.
-
Randomized trial · measured the question itselfBrustad et al., 2023The journal of allergy and clinical immunology. In practice · PubMed
Fish Oil and Vitamin D Supplementations in Pregnancy Protect Against Childhood Croup.
581 people · Pregnant women in Denmark and their children, followed to age 3
TestedHigh-dose vitamin D (2800 IU a day) vs standard dose (400 IU a day) from week 24 of pregnancy to 1 week after birth; also fish oil vs olive oil
Croup before age 3: 32 of 295 children (11%) in the high-dose vitamin D group vs 51 of 286 (18%) in the standard-dose group (hazard ratio = 0.60; 95% CI, 0.38-0.93; P = .02).
Points to benefitNo disclosure in PubMedAbstract onlyNo disclosure in PubMed.
-
Randomized trial · measured the question itselfPham et al., 2023The American journal of clinical nutrition · PubMed
Vitamin D supplementation and hospitalization for infection in older adults: A post-hoc analysis of data from the Australian D-Health Trial.
21,315 people · Australians aged 60 to 84, mean age 69, mostly not low in vitamin D
Tested60,000 IU of vitamin D3 a month vs placebo for 5 years
Hospital stays for any infection: incidence rate ratio 0.95 (95% CI 0.86, 1.05). For respiratory infection: 0.93 (0.81, 1.08). Stays longer than 6 days: 0.80 (0.65, 0.99).
No differenceNo disclosure in PubMedAbstract onlyNo disclosure in PubMed.
-
Randomized trial · measured the question itselfHuang et al., 2022Journal of microbiology, immunology, and infection = Wei mian yu gan ran za zhi · PubMed
A randomized trial of vitamin D supplementation to prevent seasonal influenza and enterovirus infection in children.
248 people · Children aged 2 to 5 in daycare in Taiwan
Tested2000 IU of vitamin D a day vs placebo for 1 month, then 6 months of follow-up
Flu risk was 84% lower with vitamin D but did not reach statistical significance (log-rank test, p = 0.055). Enterovirus infection was similar in both groups (p = 0.946).
No differenceNo stake declaredAbstract onlyNo competing interests declared.
-
Randomized trial · measured the question itselfJolliffe et al., 2022BMJ (Clinical research ed.) · PubMed
Effect of a test-and-treat approach to vitamin D supplementation on risk of all cause acute respiratory tract infection and covid-19: phase 3 randomised controlled trial (CORONAVIT).
5,979 people · People aged 16 and over in the UK not taking vitamin D
TestedOffer of a blood test and 6 months of vitamin D (800 or 3200 IU a day) if low, vs no test and no vitamin D
At least one respiratory infection: 4.6% with no offer, 5.7% with lower dose (odds ratio 1.26, 95% CI 0.96 to 1.66) and 5.0% with higher dose (1.09, 0.82 to 1.46). COVID-19: 1.39 (0.98 to 1.97) and 1.13 (0.78 to 1.63).
No differenceCompany stakeAbstract onlyFunded in part by Pharma Nord, DSM Nutritional Products, Thornton & Ross and others; lead authors report ties to vitamin D makers.
-
Randomized trial · measured the question itselfGanmaa et al., 2020The New England journal of medicine · PubMed
Vitamin D Supplements for Prevention of Tuberculosis Infection and Disease.
8,851 people · Schoolchildren in Mongolia, almost all with low vitamin D, who tested negative for tuberculosis
Tested14,000 IU of vitamin D3 a week vs placebo for 3 years
A positive tuberculosis test: 3.6% with vitamin D vs 3.3% with placebo (adjusted risk ratio, 1.10; 95% CI, 0.87 to 1.38). Hospital stays for respiratory infection: 29 vs 34 children (adjusted risk ratio, 0.86; 95% CI, 0.52 to 1.40).
No differenceNo stake declaredAbstract onlyNo potential conflict of interest reported; funded by the National Institutes of Health.
-
Randomized trial · measured the question itselfDenlinger et al., 2016American journal of respiratory and critical care medicine · PubMed
Vitamin D Supplementation and the Risk of Colds in Patients with Asthma.
408 people · Adults with mild to moderate asthma and low vitamin D
TestedVitamin D3 100,000 IU load then 4,000 IU a day vs placebo for 28 weeks
Cold severity score was no different: 62.0 on placebo vs 58.7 on vitamin D (P = 0.39). Cold rate did not differ (rate ratio, 1.2; 95% CI, 0.9-1.5). Among African Americans, colds were more frequent on vitamin D (RR, 1.7; 95% CI, 1.1-2.7).
No differenceNo disclosure in PubMedAbstract onlyNo disclosure in PubMed; funded by NIH institutes.
-
Effect of vitamin D supplementation versus placebo on recovery delay among COVID-19 Tunisian patients: a randomized-controlled clinical trial.
117 people · Adults in Tunisia with COVID-19 who still tested positive on day 14
TestedOne dose of 200,000 IU vitamin D3 vs placebo (salt water)
Median time until the virus test turned negative was 37 days with vitamin D vs 28 days with placebo (p=0.010). Hazard ratio was 1.58 (95% CI: 1.09-2.29, p=0.015).
Points to harmNo stake declaredAbstract onlyNo competing interests declared.
-
High-dose versus standard-dose vitamin D supplementation in older adults with COVID-19 (COVIT-TRIAL): A multicenter, open-label, randomized controlled superiority trial.
254 people · Adults aged 65 and older, median age 88, in hospital or nursing homes with new COVID-19 and a risk factor
TestedOne high dose of vitamin D3 (400,000 IU) vs one standard dose (50,000 IU), given within 72 hours of diagnosis
14-day deaths: 8 (6%) of 127 with high dose vs 14 (11%) of 127 with standard dose (adjusted hazard ratio = 0.39, 95% CI 0.16 to 0.99, P = 0.049). At 28 days: 19 (15%) vs 21 (17%), not clearly different (P = 0.29).
Points to benefitCompany stakeAbstract onlyMylan supplied the vitamin D3 used, and the lead author sometimes consults for Mylan.
-
The effect of vitamin D administration on vitamin D status and respiratory morbidity in late premature infants.
50 people · Babies born 3 to 7 weeks early
Tested800 IU of vitamin D3 a day vs 400 IU a day for 1 year
Doubling the dose did not raise vitamin D blood level (75.5 vs 99 nmol/L at 6 months) because of poor compliance. Babies with levels under 75 nmol/L had more breathing illness; AUC 0.745 for recorded acute respiratory illness.
MixedNo disclosure in PubMedAbstract onlyNo disclosure in PubMed.
-
Therapeutic effect of vitamin D in acute lower respiratory infection: A randomized controlled trial.
154 people · Children aged 2 months to 5 years in hospital with a lung infection
TestedOne dose of 100,000 IU vitamin D3 plus usual care vs usual care alone
No difference in hospital stay length, deaths, intensive care admission, complications or return of infection within 90 days. Vitamin D reached sufficient blood level within 72 hours.
No differenceNo disclosure in PubMedAbstract onlyNo disclosure in PubMed.
-
Vitamin D supplementation during pregnancy and infancy reduces aeroallergen sensitization: a randomized controlled trial.
185 people · Pregnant women in New Zealand and then their babies, checked at 18 months
TestedVitamin D in pregnancy and infancy (1000/400 IU or 2000/800 IU a day) vs placebo, to age 6 months
Mite allergy sensitization was lower with vitamin D. Doctor visits for asthma: 11%, 0%, 4% (placebo, lower, higher dose; P = 0.002). No group differences for other respiratory diagnoses such as colds.
No differenceNo disclosure in PubMedAbstract onlyNo disclosure in PubMed.
-
Randomized trial · lab tests or safetyMayan et al., 2015The Israel Medical Association journal : IMAJ · PubMed
Thymus Activity, Vitamin D, and Respiratory Infections in Adolescent Swimmers.
82 people · Teenage competitive swimmers, 55 of 82 with low vitamin D
TestedVitamin D3 vs placebo for 12 winter weeks, then looked at thymus (immune gland) activity and cold symptoms
Thymus activity marker did not differ by vitamin D status and was not changed by supplements. No significant links were found between this marker and how severe or long colds were.
No differenceNo disclosure in PubMedAbstract onlyNo disclosure in PubMed.
-
Exploring the Impact of COVID-19 on Ulcerative Colitis Patients: A Lifestyle Perspective.
49 people · Adults with ulcerative colitis (bowel disease) at one hospital in Latvia
TestedVitamin D use, diet and habits compared between those who had COVID-19 and those who did not
Among COVID-19 positive patients, 11 (79%) did not use vitamin D vs 3 (21%) who did (OR: 0.38 (0.07; 1.51), p = 0.28). No significant differences for supplements, vitamins or lifestyle.
No differenceNo stake declaredAbstract onlyNo conflicts of interest declared.
-
Serum 25-hydroxyvitamin D and fatty acids in relation to the risk of microbial infections in children: The TRIGR Divia study.
576 people · Babies at higher risk of type 1 diabetes, followed to 18 months
TestedVitamin D blood levels at birth and 6 to 18 months vs signs of past infections in blood tests at 18 months
Vitamin D blood level was not consistently linked to infection risk. Higher levels showed an inverse link with rotavirus antibody levels in children with rotavirus antibodies. Omega-3 fats showed more links.
No differenceNo disclosure in PubMedAbstract onlyNo disclosure in PubMed.
-
Serum Vitamin D Levels and Life-Threatening Respiratory Syncytial Virus Infection in Previously Healthy Infants.
125 people · Previously healthy babies under 12 months in hospital with their first RSV infection
TestedVitamin D blood level on admission vs needing intensive care and a breathing machine
Twenty-two of 125 infants had life-threatening disease. Their median vitamin D was 18.4 ng/mL vs 31.7 ng/mL (P < .001). Vitamin D deficiency was a risk factor (odds ratio, 11.83; 95% CI, 3.89-35.9).
Points to benefitNo stake declaredAbstract onlyNo reported conflicts of interest.
-
Association of Vitamin D Status and COVID-19-Related Hospitalization and Mortality.
4,599 people · US veterans who tested positive for the COVID-19 virus and had a vitamin D blood test
TestedVitamin D blood level before infection vs hospital stay and death within 60 days
Higher vitamin D went with fewer hospital stays (24.1 to 18.7%, p=0.009, from 15 to 60 ng/mL) and fewer deaths (10.4 to 5.7%, p=0.001) after adjusting for race and poverty.
Points to benefitNo disclosure in PubMedAbstract onlyNo disclosure in PubMed; funded by NIH institutes.
-
Infection Status of Rural Schoolchildren and its Relationship with Vitamin D Concentrations.
387 people · Rural schoolchildren near Pune, India
TestedVitamin D blood level compared with colds and other infections reported in a questionnaire
Number of upper respiratory infections was weakly linked to lower vitamin D (rs = -0.14, p < 0.05). Vitamin D sufficient children reported fewer and shorter episodes. No link with total infections.
Points to benefitNo disclosure in PubMedAbstract onlyNo disclosure in PubMed.
-
Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of stratified aggregate data.
40 studies, 61,589 people · People of all ages in 40 trials of vitamin D vs placebo
TestedAny vitamin D vs placebo or lower-dose vitamin D, any length
Vitamin D did not clearly change the risk of a respiratory infection (OR 0.94, 95% CI 0.88-1.00, p=0.057). No group effects were found by age, starting vitamin D level or dosing. Serious side effects: OR 0.96.
No differenceCompany stakeAbstract onlyOne author reports grants from Pharma Nord, DSM Nutritional Products, Cytoplan and Thornton & Ross, makers of supplements.
-
A Systematic Review Supporting the Endocrine Society Clinical Practice Guidelines on Vitamin D.
151 studies · Children, healthy adults, older adults, pregnant women and adults with prediabetes
TestedVitamin D vs no vitamin D for preventing disease, across 14 questions
In children and adolescents, low-certainty evidence suggested fewer respiratory infections with vitamin D. There was no significant effect on select outcomes in healthy adults aged 19 to 74 years.
MixedNo disclosure in PubMedAbstract onlyNo disclosure in PubMed.
-
A systematic review and meta-analysis on nutritional and dietary interventions for the treatment of acute respiratory infection in pediatric patients: An EAACI taskforce.
50 studies · Children with acute respiratory infections such as pneumonia
TestedDiet changes and supplements (zinc, vitamins A, D, E, probiotics) as treatment
Pooled results on vitamin D did not show any effect in children with pneumonia. Zinc may shorten hospital stay. No single supplement can be recommended for routine treatment.
No differenceNo disclosure in PubMedAbstract onlyNo disclosure in PubMed; funded by the European Academy of Allergy and Clinical Immunology.
-
Vitamin D supplementation to prevent acute respiratory infections: a systematic review and meta-analysis of aggregate data from randomised controlled trials.
43 studies, 48,488 people · People aged 0 to 95 years in 46 placebo-controlled trials
TestedVitamin D3, D2 or calcifediol of any dose and length, vs placebo or low-dose vitamin D
Fewer people had one or more respiratory infections with vitamin D (61.3%) than placebo (62.3%); OR 0.92 (95% CI 0.86-0.99). Daily dosing gave OR 0.78 (0.65-0.94). Serious side effects: 0.97 (0.86-1.07).
Points to benefitCompany stakeAbstract onlyAuthors report grants from Pharma Nord, DSM Nutritional Products and Cytoplan; one author had Pfizer ties.
-
Effect of micronutrient supplements on influenza and other respiratory tract infections among adults: a systematic review and meta-analysis.
Adults in trials of micronutrient supplements
TestedVitamin D, vitamin C, zinc or multiple micronutrients vs control
Vitamin D lowered the risk of respiratory infection (risk ratio 0.97; 95% CI 0.94 to 1.00; p=0.028) and shortened symptoms by 6% (95% CI -9% to -2%).
Points to benefitNo stake declaredAbstract onlyNo competing interests declared.
-
Zinc Supplementation Reduces Common Cold Duration among Healthy Adults: A Systematic Review of Randomized Controlled Trials with Micronutrients Supplementation.
20 studies · Healthy adults in 20 trials of single micronutrients
TestedZinc, vitamin D, vitamins A and E by mouth, vs control
Micronutrients except vitamin C may not prevent colds or reduce symptom severity. Zinc may cut cold length by 2.25 days (95% CI: -3.39, -1.12). Vitamin D results are not given on their own.
No differenceNo disclosure in PubMedAbstract onlyNo company tie mentioned; no clear conflict statement.
-
Pooled review (meta-analysis)Martineau et al., 2019Health technology assessment (Winchester, England) · PubMed
Vitamin D supplementation to prevent acute respiratory infections: individual participant data meta-analysis.
25 studies, 10,933 people · People aged 0 to 95 years in 25 placebo-controlled trials
TestedVitamin D3 or D2 pills of any dose and length, vs placebo
Vitamin D lowered the risk of a respiratory infection (adjusted odds ratio 0.88, 95% CI 0.81 to 0.96). Daily or weekly doses gave 0.81; bolus doses gave 0.97. Starting level <25 nmol/l gave 0.30.
Points to benefitCompany stakeAbstract onlySome authors report grants or fees from GSK, Pfizer, Sanofi, Vifor and Laboratoires SMB; main funder was the UK NIHR.
-
Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data.
25 studies, 10,933 people · People aged 0 to 95 years in 25 placebo-controlled trials
TestedVitamin D3 or D2 pills of any dose and length, vs placebo
Vitamin D lowered the odds of a respiratory infection (adjusted odds ratio 0.88, 95% CI 0.81 to 0.96). Benefit was seen with daily or weekly doses (0.81) but not with bolus doses (0.97), and was larger when starting level was <25 nmol/L (0.30).
Points to benefitNo stake declaredAbstract onlyNo competing interests declared; funded by the UK National Institute for Health Research.
-
Vitamin D in the prevention or treatment of COVID-19.
People at risk of or sick with COVID-19
TestedReview of vitamin D supplements and blood levels for preventing or treating COVID-19
Observational studies link higher vitamin D to lower COVID-19 risk, but genetic studies were null and trials were inconsistent. Current evidence is insufficient to support routine use of vitamin D supplements for COVID-19.
No weight on the ladderNo disclosure in PubMedAbstract onlyNo disclosure in PubMed.
-
Clinical aspects of SARS-CoV-2 infection and vitamin D : COVID-19 and the endocrine system: special issue for reviews in endocrine and metabolic disorders (Felipe Casaneuva, Editor in Chief) A. Giustina and JP Bilezikian, Guest Editors.
People with COVID-19
TestedReview of studies linking vitamin D status to COVID-19
Most observational and cohort studies link low vitamin D to worse COVID-19. The few trials give inconsistent results. The authors await larger randomized trials.
No weight on the ladderCompany stakeAbstract onlyOne author leads a vitamin D deficiency study in Brazil sponsored by Mantecorp, a drug company.
-
Role of vitamin D in preventing of COVID-19 infection, progression and severity.
People at risk of COVID-19 and other respiratory infections; 20 European countries
TestedReview of vitamin D and COVID-19 and other respiratory infections, plus a country-level comparison of average vitamin D vs COVID-19 cases
Countries with lower average vitamin D had more COVID-19 cases per million (p=0.033) but not more deaths. The author says there is not enough evidence on vitamin D and COVID-19 severity and mortality.
No weight on the ladderNo disclosure in PubMedAbstract onlyNo disclosure in PubMed.
-
Asthma, allergy and respiratory infections: the vitamin D hypothesis.
Children and adults with asthma, allergy or respiratory infections
TestedReview of studies on vitamin D and asthma, allergy and respiratory infections
Studies show low vitamin D blood levels linked to higher risk of upper and lower respiratory infections in children. The authors call for controlled trials of supplements.
No weight on the ladderNo disclosure in PubMedAbstract onlyNo disclosure in PubMed.
9 papers we read and set aside as off topic
- Moon, 2023. Gut distress and intervention via communications of SARS-CoV-2 with mucosal exposome. (opinion or narrative review)
- Crawford et al., 2022. Select Dietary Supplement Ingredients for Preserving and Protecting the Immune System in Healthy Individuals: A Systematic Review. (systematic review)
- Velayati et al., 2025. Clinical randomized trial of vitamin D and C supplementation in critically ill patients with respiratory failure. (randomized trial)
- Hadji et al., 2014. Effect of adjuvant endocrine therapy on hormonal levels in premenopausal women with breast cancer: the ProBONE II study. (randomized trial)
- Majak et al., 2011. Vitamin D supplementation in children may prevent asthma exacerbation triggered by acute respiratory infection. (randomized trial)
- Goldring et al., 2013. Prenatal vitamin d supplementation and child respiratory health: a randomised controlled trial. (randomized trial)
- Grayeb et al., 2025. Long-Term Outcomes of Children Receiving Percutaneous Endoscopic Gastrostomy Feeding. (population study: followed a group)
- AlEnzi et al., 2021. Fibromyalgia in Health Care Worker During COVID-19 Outbreak in Saudi Arabia. (population study: one-time survey)
- Sempos et al., 2021. Adjusting Coronavirus Prevalence Estimates for Laboratory Test Kit Error. (other)
Words on this page
- Hazard ratio (HR)
- Compares how often something happened in two groups over time. 1 means no difference. 0.80 means 20% lower risk; 1.20 means 20% higher.
- Relative risk (RR)
- Compares the risk in two groups. 1 means no difference. 0.85 means 15% lower risk.
- Odds ratio (OR)
- Another way to compare two groups. 1 means no difference. Below 1 means lower odds, above 1 higher odds.
- 95% CI (confidence interval)
- The range where the true result likely lies. If the range includes no effect (1 for ratios, 0 for differences), the result is not clear.
- p-value (p =)
- How likely a result this large would be by chance if there were no real effect. Below 0.05 is usually called a clear result.
- Placebo
- A dummy pill or fake treatment, so people do not know which group they are in.
- Pooled review (meta-analysis)
- A study that combines the results of many earlier studies to get one overall answer.
- Cohort study
- A study that follows a large group of people over years. It shows links, not causes.
- Marker
- A lab or scan result that stands in for a health outcome. A better marker does not always mean better health.
How the short answer is set
Fixed rules turn the studies into the short answer, so the same studies always give the same answer. The rules start from GRADE, a standard system for rating evidence, in plain language.
| Confidence | What it means |
|---|---|
| High | We are confident the answer is right. |
| Moderate | The answer is probably right, but it could change. |
| Low (this page) | The answer may well change. |
| Very low | Any answer is very uncertain. |
| Not tested in people | Only cell or animal studies exist. |
Why low here
- Placebo trials in people counted infections directly, so the rating starts high.
- Results disagree: 2017 and 2021 pools found a small benefit; the 2025 update did not.
- Imprecise: the newest pooled range runs from a small benefit to no effect.
- The 2025 review's funnel plot was lopsided, a sign small trials may skew results.
How this page was made
Label
- Search
- PubMed, Nov 14, 2026. Searches written by Claude Opus 5.5; papers ranked by PubMed
- First read of all 42 papers
- Claude Sonnet
- Independent second read
- Claude Haiku
- Disagreements settled by
- Claude Opus 5.5
- Page text written by
- Claude Opus 5.5
- Charts
- Drawn by code from the study records
- Source check by a person
- Not yet. Required before search engines may list this page.
- Expert review
- No
- Papers read in full
- 0 of 42; all from PubMed abstracts
- Method
- v0.2, created Nov 14, 2026
Search. We ran four PubMed searches for vitamin D supplements and colds, flu and other respiratory infections: pooled and systematic reviews since 2012 (10 of 95), trials in people (22 of 102), population studies (10 of 162). The first number is how many papers we read; the second is how many PubMed found. We took the ones PubMed ranks as most relevant. See the full PubMed search. Of the 42 papers read, 33 were on topic.
Limits. Digestery reads at most about 60 papers per question, so large fields are sampled, not covered in full. Abstracts can leave out key details, such as side effects and funding.
Review queue
These items wait for a person. Search engines are asked not to list the page until the first one is done.
- OpenThe short answer is new. It waits for a source check by a person.
- OpenDuplicate: Martineau 2017 and Martineau 2019 report the same individual-data analysis (25 trials, PROSPERO CRD42014013953). Counted once.
- OpenOverlap: Jolliffe 2021 updates the 2017 trials and Jolliffe 2025 adds new trials to its 43; treat the three pools as one evolving analysis.
- OpenOverlap: VITAL (Camargo 2024, 15 804 people) is the large new trial inside the 2025 pool Jolliffe 2025; trial and pool are not independent.
- OpenUnknown overlap: abstracts do not say whether Ganmaa 2020, Reyes 2024, Clerico 2025 or Abioye 2021's trials sit inside the Jolliffe pools.
- OpenDisclosure mismatch: Martineau 2017 declares no relevant ties; the same analysis Martineau 2019 lists GSK, Pfizer, Sanofi, Vifor and Laboratoires SMB. Check.
- OpenAbroug 2023: hazard ratio 1.58 may describe faster clearance, while medians show slower. Check the full text for direction.
- OpenBandeira 2022: stake rests on Mantecorp sponsoring a vitamin D study; the abstract does not say Mantecorp sells vitamin D.
- OpenNo PubMed disclosure for trials Pham 2023, Denlinger 2016, Brustad 2023, Grant 2016, Mayan 2015, Golan-Tripto 2020, Somnath 2017; check full texts for company ties.
- OpenUnsure on relevance: Wang 2020 set relevant (vitamin D not reported alone); Mayan 2015 reports no vitamin D effect on colds; Velayati 2025 set off-topic.
- OpenChanged n: Jolliffe 2022 to 5979 analyzed, Brustad 2023 to 581 in the vitamin D comparison. Confirm against full texts.
- OpenMeltzer 2026 abstract lists registration NCT0486890; registration line says NCT04868903. Likely a typo in the abstract.
Page history
| Date | Change | Reason |
|---|---|---|
| Nov 14, 2026 | Page created from 42 papers. | First version of the page. |
Flag an error
A flag must point to a source: the passage in the paper, or a link to a study this page missed. A flag starts a new check. Votes never change a page.