Most of us know about vitamin D as vital for calcium metabolism and the importance of vitamin D for long term bone health. There are a number of indications for an association between vitamin D deficiency and infectious diseases from observational studies. This includes infectious diseases like tuberculosis, respiratory tract infections (RTI), influenza and sepsis. Other observational studies have been done in many other areas as well. Randomized controlled trials (RCT) with vitamin D supplementation for treatment and/or prevention of infections have not given conclusive results.
The current study is a five year intervention study with vitamin D subjects with prediabetes for the prevention of the progression of their type 2 diabetes. A part of that study included six month assessments of upper respiratory infections (URI) and urinary tract infections (UTI).
Five hundred and eleven individuals with prediabetes were randomized to one capsule of vitamin D (cholecalciferol 20,000 IU) per week or placebo for 5 years. A questionnaire on RTI and UTI was done every 6 months. The average baseline serum 25 hydroxyvitamin D level was 60 nmol/L. One hundred and sixteen in the vitamin D group and 111 in the placebo group completed the 5 year study. In regards to UTIs, 18 in the vitamin D group and 34 in the placebo group reported UTI during the study. There were no significant differences for RTI. The effect for UTI was more pronounced in men. The effect of vitamin D on UTI was unrelated to the baseline serum vitamin D level.
To my knowledge, this is the first RCT reporting an effect on vitamin D and UTI although there are several observational reports showing an association between vitamin D deficiency to UTI. In one case control study, adults with UTI had 28% lower serum levels than controls. In another study, children with a UTI had serum vitamin D levels half that of the controls, which was also observed in a study of premenopausal women.
One wonders what the mechanisms might be for a protective effect of vitamin D on UTI. There are several possibilities. One could be that vitamin D can induce production and secretion of an antimicrobial peptide by bladder epithelial cells. Another might be that vitamin D is important for innate immunity in defending against bacterial infections by increasing white blood cell motility and phagocytic action. Vitamin D could also alter the chemical composition of the urine by increasing urinary calcium excretion. Vitamin D also has a direct effect on muscle function which can contribute to pelvic floor support and bladder emptying, especially in women.
There is a robust amount of observational studies noting the role of vitamin D on health and a possible association of reducing the risks of a wide array of diseases. It seems that higher serum levels of vitamin D provide benefits. However, we have a long way to go in proving the role of vitamin D supplementation as an intervention.
Reference: Jorde R, Sollid S, Svartgberg J, et al. Prevention of urinary tract infections with vitamin D supplementation 20,000 iu per week for five years. Results from an RCT including 511 subjects. Infections Diseases 2016;48 (11-12): 823-828.