Earlier, I wrote that autism was linked to vitamin D deficiency in pregnant mothers, and that women's cancers were dramatically reduced by regular sunlight exposure. Now, research indicates that the risk of placental infection is impressively lowered by increasing vitamin D levels.
This research did not surprise me. Immunity is enhanced by high vitamin D levels through the increased production of an antimicrobial peptide called cathelicidin, which keeps both bacterial and viral infections at bay. This is the exact reason that flu occurs almost exclusively in winter months in both hemispheres; blood levels of vitamin D are much lower in winter months (see my earlier posts)
In this research, placental cells were exposed to E. coli bacteria and then treated with vitamin D. The treatment reduced the risk of infection by about 50%.
Remember that there is also a dramatic reduction in the risk of breast and ovarian cancer among women with high sunlight exposure and high vitamin D levels; now we can add one more advantage of vitamin D to the list of benefits for female reproductive tissue.
 Liu, N. et al. Vitamin D Induces Innate Antibacterial Responses in Human Trophoblasts via an Intracrine Pathway. Biol Reprod 2008 Nov 12. [Epub ahead of print]