Every study we read on this question

Trials in people (16)

• Trial in 923 Chicago adults: vitamin D doses did not clearly change COVID-19 risk
  Randomized trial2026923 peopleNo difference
• 24-week trial in 189 healthy Danish children: vitamin D cut respiratory infection sick days
  Randomized trial2025189 peoplePoints to benefit
• 52-week trial in 15,804 older adults: vitamin D did not clearly change colds
  Randomized trial202415,804 peopleNo difference
• 6-month trial in 303 Chilean children: vitamin D did not clearly change respiratory infections
  Randomized trial2024303 peopleNo difference
• Trial in 581 pregnant Danish women: high-dose vitamin D, less croup by age 3
  Randomized trial2023581 peoplePoints to benefit
• 5-year trial in 21,315 older Australians: no clear change in infection hospital stays
  Randomized trial202321,315 peopleNo difference
• 4-week trial in 248 daycare children in Taiwan: no clear difference in flu risk
  Randomized trial2022248 peopleNo difference
• 26-week trial in 5,979 UK adults offered vitamin D: no clear fall in infections
  Randomized trial20225,979 peopleNo difference
• 3-year trial in 8,851 Mongolian children: vitamin D, no clear change in tuberculosis tests
  Randomized trial20208,851 peopleNo difference
• 28-week trial in 408 adults with asthma: vitamin D did not clearly change colds
  Randomized trial2016408 peopleNo difference
• Trial in 117 Tunisian adults with COVID-19: vitamin D lengthened time to negative test
  Randomized trial2023117 peoplePoints to harm
• Trial in 254 older adults with COVID-19: more vitamin D, fewer 14-day deaths
  Randomized trial2022254 peoplePoints to benefit
• Trial in 50 babies born early: mixed results for vitamin D and breathing illness
  Randomized trial202050 peopleMixed
• Trial in 154 hospitalized children: one vitamin D dose, no clear difference in outcomes
  Randomized trial2017154 peopleNo difference
• Trial in 185 pregnant women in New Zealand: no clear difference in colds
  Randomized trial2016185 peopleNo difference
• 12-week trial in 82 teenage swimmers: vitamin D left immune gland activity unchanged
  Randomized trial201582 peopleNo difference

Population studies (1)

• In 49 adults with bowel disease, vitamin D use showed no clear COVID-19 link
  Population study: one-time survey202449 peopleNo difference

Blood and genes (4)

• Study of 576 babies: vitamin D blood levels had no consistent link to infections
  Blood level study2022576 peopleNo difference
• Study of 125 hospitalized babies with RSV: low vitamin D linked to life-threatening illness
  Blood level study2022125 peoplePoints to benefit
• In 4,599 US veterans with COVID-19, higher vitamin D levels went with fewer deaths
  Blood level study20224,599 peoplePoints to benefit
• Study of 387 rural Indian schoolchildren: lower vitamin D weakly linked to more colds
  Blood level study2019387 peoplePoints to benefit

Reviews (8)

• Pooled review of 40 vitamin D trials, 61,589 people: no clear change in infections
  Pooled review (meta-analysis)202561,589 peopleNo difference
• Review of 151 studies: vitamin D gave mixed results, with possible benefit in children
  Systematic review2024Mixed
• Pooled review of 50 studies: vitamin D did not clearly change pneumonia in children
  Pooled review (meta-analysis)2024No difference
• Pooled review of 43 trials, 48,488 people: slightly fewer respiratory infections with vitamin D
  Pooled review (meta-analysis)202148,488 peoplePoints to benefit
• Pooled review of trials: vitamin D slightly lowered infection risk and shortened symptoms
  Pooled review (meta-analysis)2021Points to benefit
• Review of 20 trials in healthy adults found no clear cold prevention from supplements
  Systematic review2020No difference
• 2019 pooled review of 25 trials: vitamin D lowered the risk of respiratory infection
  Pooled review (meta-analysis)201910,933 peoplePoints to benefit
• Pooled review of 25 trials found vitamin D lowered the odds of respiratory infection
  Pooled review (meta-analysis)201710,933 peoplePoints to benefit

Opinion (4)

• Review of vitamin D and COVID-19 found no clear support for routine supplement use
  Opinion or narrative review2023No difference
• Review of vitamin D and COVID-19: low levels linked to worse illness, trials inconsistent
  Opinion or narrative review2022Mixed
• Review and 20-country comparison: lower vitamin D linked to more COVID-19 cases, not deaths
  Opinion or narrative review2020Mixed
• 2012 review: low vitamin D blood levels linked to more respiratory infections in children
  Opinion or narrative review2012Points to benefit