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Acute respiratory infection treated by vitamin D in 6 of 12 clinical trials – review Nov 2012

Vitamin D in the Prevention of Acute Respiratory Infection: A Systematic Review of Clinical Studies

Thorax 2012;67:A71-A72
Poster session 19 Clinical observations in acute and chronic lung infection
DA Jolliffe, AR Martineau, CJ Griffiths
Barts and The London School of Medicine and Dentistry, London, England

Introduction and Objectives Acute respiratory infections (ARI) cause significant morbidity and mortality: in the UK, during 2004, 33,957 deaths occurred due to pneumonia alone. Vitamin D metabolites enhance immunity to a wide range of respiratory pathogens in vitro, and numerous clinical studies have investigated whether vitamin D deficiency is a risk factor for ARI, or whether vitamin D supplementation prevents ARI. Systematic reviews of this literature are lacking, however. Our objective was to conduct a systematic review of clinical studies investigating the relationship between vitamin D status or the effect of vitamin D supplementation on risk of ARI.

Methods The PubMed database was searched on 7th June 2012 using the terms ‘vitamin D’ and’ respiratory infection’. Cross-sectional studies, case-control studies, cohort studies or clinical trials in human subjects investigating the relationship between serum concentration of vitamin D metabolites or the effect of vitamin D supplementation on risk of ARI were included; ARI was defined as any infection of the respiratory tract with symptom duration of 30days or less. Studies relating exclusively to tuberculosis were excluded, as this is classically regarded as a chronic respiratory tract infection, with symptom duration usually exceeding 30 days.

Results Thirty-one studies reporting data from a total of 43,272 participants were included in our review. Of these,

  • 19 were observational studies (3 cross-sectional, 8 case-control and 8 cohort) and
  • 12 were randomised controlled trials.

Sixteen of the 19 observational studies reviewed reported statistically significant associations between vitamin D deficiency and susceptibility to ARI, and 3 reported no such association.

Six of the 12 clinical trials reviewed reported protective effects of vitamin D against ARI, while five reported null effects, and one reported an adverse effect on pneumonia recurrence.

Conclusions Observational studies report consistent associations between vitamin D deficiency and susceptibility to ARI in a wide range of age-groups in diverse clinical settings. By contrast, randomised controlled trials of vitamin D supplementation for the prevention of ARI report conflicting results, possibly reflecting varying prevalence of vitamin D deficiency in study populations and/or heterogeneity in vitamin D supplementation regimens investigated.
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This kind of systematic review must group all clinical trials together. For example: the trials which were successful with 5,000 IU are grouped with the ones which found that 100 IU did not help. Likewise, successful trials which treated ARI for 6 months are diluted with trials which failed to treat after 6 weeks. Also, successful trials which were made on populations which were deficient are grouped with trials which were made of populations which were already vitamin D sufficient.

See also VitaminDWiki