A claim you hear on longevity podcasts
The claim checked: Getting vitamin D levels over 50 cuts flu risk by 75%, more than a flu shot Hear it at 1:14
Four of ten studies found no protection from vitamin D against flu or other respiratory infections, and six partly backed it. Two trials found fewer flu cases with it, and the largest drop in this set was 50%.
Computed from 10 studies that test this point, each judged by two readers, in full. 9 more studies are waiting for a full read and do not count yet.
“that if you're low you you you're at higher risk for the flu and by getting the vitamin D up over 50 your risk your risk of flu goes down by 75% that's more than a flu shot”
None.
other primary study · 2010
“A vitamin D concentration ≥38 ng/ml approximately halved the risk for development of an acute viral respiratory tract infection over the observation period (p<0.0001).”
Serum 25-hydroxyvitamin d and the incidence of acute viral respiratory tract infections in healthy adults. PLoS One
Who: Healthy adults aged 20-88 living or working near Greenwich, CT, without chronic disease, followed fall-winter 2009-2010
PMID 20559424
other primary study · 2011
“From participants with 25(OH)D concentrations < 25 nmol/l and from those with >100 nmol/l, 11·5 % and 6 %, respectively, had an infection during the preceding month.”
Vitamin D status has a linear association with seasonal infections and lung function in British adults. Br J Nutr
Who: 6789 Caucasian British adults aged 45 from the 1958 British birth cohort
PMID 21736791
pooled analysis · 2019
“Our findings suggest an important role of vitamin D in prevention of ARTI risk and severity, particularly in people with low 25(OH)D concentration.”
Acute Respiratory Tract Infection and 25-Hydroxyvitamin D Concentration: A Systematic Review and Meta-Analysis. Int J Environ Res Public Health
Who: Adolescents and adults aged 12 years and older in observational (cohort, case-control, cross-sectional) studies; ARI including influenza, colds and pneumonia
PMID 31438516
other primary study · 2023
“Serum 25(OH)D concentrations are inversely associated with respiratory infection occurrence among United States adults.”
Association between Serum 25-Hydroxyvitamin D Concentrations and Respiratory Infection among United States Adults. J Nutr
Who: 31,466 US adults aged 20 and older in NHANES 2001-2014 (weighted mean age 47.1, 55.5% women)
PMID 36913460
controlled trial · 2010 · landmark
“Influenza A occurred in 18 of 167 (10.8%) children receiving vitamin D3 compared with 31 of 167 (18.6%) children receiving placebo (RR: 0.58; 95% CI; 0.34, 0.99; P = 0.04) (Table 2).”
Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr
Who: 430 randomized Japanese schoolchildren aged 6-15 (334 analysed), with or without underlying disease
PMID 20219962
controlled trial · 2017
“The prespecified comparison of the incidence of influenza (influenza A and influenza B combined) revealed that the incidence of influenza infections in the high-dose group was reduced by 50% (incidence RR, 0.50; 95% CI, 0.28-0.89; Table 2).”
Effect of High-Dose vs Standard-Dose Wintertime Vitamin D Supplementation on Viral Upper Respiratory Tract Infections in Young Healthy Children. JAMA
Who: Healthy children aged 1-5 years in Toronto primary care practices (TARGet Kids!)
PMID 28719693
other primary study · 2014
“In conclusion, low serum 25(OH)D concentration was not associated with recent RTI symptoms.”
Association between serum 25-hydroxyvitamin D concentration and symptoms of respiratory tract infection in a Norwegian population: the Tromsø Study. Public Health Nutr
Who: 6,350 middle-aged and elderly residents of Tromsø, Norway (69°N), mean age 63.7, Tromsø Study 6
PMID 23659381
other primary study · 2016
“We did not find a correlation between serum 25(OH)D concentrations and the risk of influenza virus infection.”
Serum 25-Hydroxyvitamin D Was Not Associated with Influenza Virus Infection in Children and Adults in Hong Kong, 2009-2010. J Nutr
Who: 3030 children and adults of all ages from 796 households in Hong Kong enrolled in a household influenza vaccine trial, 2009-2010
PMID 27798334
controlled trial · 2019
“Our results show that vitamin D supplementation does not reduce influenza but can reduce non‐influenza respiratory infections in children and adolescents aged 3‐17 years in a low‐ and middle‐income country.”
Effect of Vitamin D supplementation to reduce respiratory infections in children and adolescents in Vietnam: A randomized controlled trial. Influenza Other Respir Viruses
Who: 1300 healthy children and adolescents aged 3-17 in rural Thanh Liem district, Vietnam
PMID 30328294
pooled analysis · 2025
“In summary, this updated meta-analysis of data from RCTs of any vitamin D supplementation for the prevention of ARI yielded a similar point estimate for the overall effect of vitamin D supplementation on ARI risk to that obtained previously, but the 95% CI for this effect now includes 1·00, indicating no statistically significant protection.”
Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of stratified aggregate data. Lancet Diabetes Endocrinol
Who: participants from birth to 100 years in double-blind placebo-controlled RCTs of vitamin D for primary prevention of acute respiratory infection, in 24 countries
PMID 39993397
Eight of ten studies linked low blood vitamin D to more respiratory infections, including flu, mostly in observational data; one found no link.
Computed from 10 studies that test this point, each judged by two readers, in full. 3 more studies are waiting for a full read and do not count yet.
other primary study · 2009 · landmark
“Even after adjusting for demographic and clinical characteristics, lower 25(OH)D levels were independently associated with recent URTI (compared with 25[OH]D levels of ≥30 ng/mL: odds ratio [OR], 1.36; 95% CI, 1.01–1.84 for <10 ng/mL and 1.24; 1.07–1.43 for 10 to <30 ng/mL).”
Association between serum 25-hydroxyvitamin D level and upper respiratory tract infection in the Third National Health and Nutrition Examination Survey. Arch Intern Med
Who: Nationally representative US civilian noninstitutionalized participants aged 12 and older (NHANES III, 1988-1994), median age 38
PMID 19237723
other primary study · 2010
“A vitamin D concentration ≥38 ng/ml approximately halved the risk for development of an acute viral respiratory tract infection over the observation period (p<0.0001).”
Serum 25-hydroxyvitamin d and the incidence of acute viral respiratory tract infections in healthy adults. PLoS One
Who: 198 healthy adults aged 20-88 (85 men, 113 women) in Greenwich, CT, followed fall-winter 2009-2010
PMID 20559424
other primary study · 2020
“Experimental evidence and observations in large cohorts are generally consistent that vitamin D deficiency (<50 nmol/L [<20 ng/mL]) and insufficiency (<75 nmol/L [<30 ng/mL]) of serum 25-hydroxycholecalciferol (25-OHD) concentration is associated with increased risk of ARTI, and supplementation for those with deficiency/insufficiency may lead to clinically meaningful reductions in the incidence of ARTI.”
The effects of vitamin D on acute viral respiratory infections: A rapid review. Adv Integr Med
Who: rapid review of 20 systematic reviews/meta-analyses of vitamin D and acute respiratory tract infections in children and adults
PMID 32837896
other primary study · 2023
“In a nationally representative sample of United States adults, low serum 25(OH)D concentrations were associated with high probability of a head or chest cold and a respiratory infection, including influenza, pneumonia, or ear infection, after adjusting for sociodemographic characteristics, dietary and lifestyle factors, BMI, and season of examination.”
Association between Serum 25-Hydroxyvitamin D Concentrations and Respiratory Infection among United States Adults. J Nutr
Who: 31,466 US adults aged 20 and older in NHANES 2001-2014 (weighted mean age 47.1, 55.5% women)
PMID 36913460
trial or observed group · 2024
“Interestingly, the participants with vitamin D insufficiency at baseline had a 2.1-fold risk of having 2 or more ARIs and a 2.3-fold risk of having 6 or more days off duty because of ARI when controlled for possible confounding factors.”
Effects of Vitamin D Supplementation and Baseline Vitamin D Status on Acute Respiratory Infections and Cathelicidin: A Randomized Controlled Trial. Open Forum Infect Dis
Who: Healthy young Finnish male military conscripts aged 18-29 (mean 19)
PMID 39301110
systematic review · 2023 · landmark
“Vitamin D deficiency leads to a dysfunctional immune system, creating increased susceptibility to bacterial infections, mainly intracellular bacterial infections [ 104 , 105 ], such as mycobacteria tuberculosis [ 106 , 107 ], and a variety of viral infections, including influenza A [ 40 , 105 , 108 ] ( Table 1 ).”
Infections and Autoimmunity-The Immune System and Vitamin D: A Systematic Review. Nutrients
Who: narrative synthesis of RCTs, observational and lab studies on vitamin D, infection and autoimmunity
PMID 37686873
other primary study · 2011
“Each 10 nmol/l increase in 25(OH)D was associated with a 7 % lower risk of infection (95 % CI 3, 11 %) after adjustment for adiposity, lifestyle and socio-economic factors.”
Vitamin D status has a linear association with seasonal infections and lung function in British adults. Br J Nutr
Who: 6789 Caucasian British adults aged 45 from the 1958 British birth cohort
PMID 21736791
pooled analysis · 2019
“There was a significantly higher risk of ARTI in the lowest compared with the highest 25(OH)D category (pooled OR 1.83; 95% CI 1.42–2.37; I 2 = 78.8%; p < 0.001) ( Figure 2 ).”
Acute Respiratory Tract Infection and 25-Hydroxyvitamin D Concentration: A Systematic Review and Meta-Analysis. Int J Environ Res Public Health
Who: Adolescents and adults aged 12 years and older in observational (cohort, case-control, cross-sectional) studies; ARI including influenza, colds and pneumonia
PMID 31438516
other primary study · 2010
“The data support the hypothesis that high fluences of UVB radiation (vitamin D level), as occur in the summer, act in a protective manner with respect to influenza.”
The seasonality of pandemic and non-pandemic influenzas: the roles of solar radiation and vitamin D. Int J Infect Dis
Who: population-level influenza incidence and death data from Sweden, Norway, USA, Singapore and Okinawa compared with modelled UVB/vitamin D photosynthesis
PMID 21036090
other primary study · 2014
“In conclusion, low serum 25(OH)D concentration was not associated with recent RTI symptoms.”
Association between serum 25-hydroxyvitamin D concentration and symptoms of respiratory tract infection in a Norwegian population: the Tromsø Study. Public Health Nutr
Who: 6,350 middle-aged and elderly residents of Tromsø, Norway (69°N), mean age 63.7, Tromsø Study 6
PMID 23659381
The Precis Weekly
One email a week with the claims and episodes we checked, what the studies found and the minute each claim was said.
Free. Unsubscribe anytime.