Prevention of urinary tract infections with vitamin D supplementation 20,000IU per week for five years. Results from an RCT including 511 subjects

Background: In observational studies vitamin D deficiency is associated with increased risk of infections, whereas the effect of vitamin D supplementation in randomized controlled trials is non-conclusive. Methods: Five hundred and eleven subjects with prediabetes were randomized to vitamin D-3 (20,000IU per week) versus placebo for five years. Every sixth month, a questionnaire on respiratory tract infections (RTI) (common cold, bronchitis, influenza) and urinary tract infection (UTI) was filled in. Results: Mean baseline serum 25-hydroxyvitamin D (25(OH)D) level was 60nmol/L. Two hundred and fifty-six subjects received vitamin D and 255 placebo. One hundred and sixteen subjects in the vitamin D and 111 in the placebo group completed the five-year study. Eighteen subjects in the vitamin D group and 34 subjects in the placebo group reported UTI during the study (p<0.02), whereas no significant differences were seen for RTI. The effect on UTI was most pronounced in males. The effect of vitamin D on UTI was unrelated to baseline serum 25(OH)D level. Conclusion: Supplementation with vitamin D might prevent UTI, but confirmatory studies are needed.