INTERPRETATION Results indicate that vitamin D has a protective effect against RTI , and dosing once-daily seems most effective .
BACKGROUND Low levels of 25-OH vitamin D are associated with  respiratory tract infection ( RTI ) .
However , results from r and omized controlled trials are inconclusive .
Therefore , we performed a systematic review and meta- analysis to assess the preventive effect of vitamin D supplementation on RTI .
High Doses of Vitamin D to Reduce Exacerbations in Chronic Obstructive Pulmonary Disease
BACKGROUND Low serum 25-hydroxyvitamin D ( 25-[OH]D ) levels have been associated with lower FEV(1 ) , impaired immunologic control , and increased airway inflammation . Because many patients with chronic obstructive pulmonary disease ( COPD ) have vitamin D deficiency , effects of vitamin D supplementation may extend beyond preventing osteoporosis . OBJECTIVE To explore whether supplementation with high doses of vitamin D could reduce the incidence of COPD exacerbations . DESIGN R and omized , single-center , double-blind , placebo-controlled trial . ( Clinical Trials.gov registration number : NCT00666367 ) SETTING University Hospitals Leuven , Leuven , Belgium . PATIENTS 182 patients with moderate to very severe COPD and a history of recent exacerbations . INTERVENTION 100,000 IU of vitamin D supplementation or placebo every 4 weeks for 1 year . MEASUREMENTS The primary outcome was time to first exacerbation . Secondary outcomes were exacerbation rate , time to first hospitalization , time to second exacerbation , FEV(1 ) , quality of life , and death . RESULTS Mean serum 25-(OH)D levels increased significantly in the vitamin D group compared with the placebo group ( mean between-group difference , 30 ng/mL [ 95 % CI , 27 to 33 ng/mL ] ; P < 0.001 ) . The median time to first exacerbation did not significantly differ between the groups ( hazard ratio , 1.1 [ CI , 0.82 to 1.56 ] ; P = 0.41 ) , nor did exacerbation rates , FEV(1 ) , hospitalization , quality of life , and death . However , a post hoc analysis in 30 participants with severe vitamin D deficiency ( serum 25-[OH]D levels < 10 ng/mL ) at baseline showed a significant reduction in exacerbations in the vitamin D group ( rate ratio , 0.57 [ CI , 0.33 to 0.98 ] ; P = 0.042 ) . LIMITATION This was a single-center study with a small sample size . CONCLUSION High-dose vitamin D supplementation in a sample of patients with COPD did not reduce the incidence of exacerbations . In participants with severe vitamin D deficiency at baseline , supplementation may reduce exacerbations . PRIMARY FUNDING SOURCE Applied Biomedical Research Program , Agency for Innovation by Science and Technology ( IWT-TBM )
INTERPRETATION Results indicate that vitamin D has a protective effect against RTI , and dosing once-daily seems most effective .
BACKGROUND Low levels of 25-OH vitamin D are associated with  respiratory tract infection ( RTI ) .
However , results from r and omized controlled trials are inconclusive .
Therefore , we performed a systematic review and meta- analysis to assess the preventive effect of vitamin D supplementation on RTI .