“This could make [25-hydroxyvitamin D3 (25D3)] an effective and safe way of activating the endogenous antimicrobial response locally at the site of infection,” wrote researchers from the Karolinska Institutet and Karolinska University Hospital in Stockholm. “Determining the vitamin D status of individuals with a history of UTI may be of importance to evaluate their ability to fend off intruding bacteria.
“Supplementation to restore proper vitamin D levels may therefore help preparing the bladder epithelium to mount a stronger and faster immune response once bacteria enter the bladder.”
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
And the science supports maintaining adequate levels, with vitamin D deficiency in adults reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 diabetes.
The new study indicates that the benefits of the sunshine vitamin may also extend to urinary tract health – a health category traditionally dominated by cranberry juice and extracts.
The Stockholm-based scientists analyzed vitamin D blood levels in 22 postmenopausal and six premenopausal Swedish women. An additional eight women with a median age of 62 were recruited to participate in a supplementation trial (2000 units per day of 25D3 for 12 weeks, Recip, Meda Pharmaceuticals). Five women completed the trial.
The Swedish researchers note that 1,25(OH)2D was measured in bladder cell cultures, which indicated that the cells of the bladder are capable of producing the active form of the vitamin.
Results from the supplementation trial showed that 25-hydroxyvitamin D3 was associated with an induction in the expression of cathelicidin when bladder biopsies were exposed to E. coli. No general induction of the antimicrobial peptide was observed during vitamin D supplementation, added the researchers.
“Here we show that oral 25D3 supplementation of healthy postmenopausal women prepares the bladder tissue to fight E. coli infection by increased production of cathelicidin upon bacterial contact,” report the researchers. “25D3 is locally converted to 1,25D3 in bladder epithelial cells, binds to vitamin D receptor, which leads to […] synthesis of cathelicidin.
“The increased production in turn enhances the direct antibacterial effect on uropathogenic E. coli,” they added.
An alternative to antibiotics
“In light of the emerging resistance to antibiotics used against UTI, new treatment strategies are needed,” report the researchers. “Our data suggest that vitamin D can stimulate an increased production of the antimicrobial peptide cathelicidin. By inducing and activating cathelicidin with vitamin D, a local rather than a systemic effect can be achieved.
“This could offer selective and site-specific treatment of pathogens without perturbing commensal microbes elsewhere in the body.”
Source: PLoS ONE