Relatively high serum vitamin D levels do not impair the antibody response to encapsulated bacteria.

Vitamin D skews the immune system towards a more tolerogenic state. Therefore, a relatively high vitamin D status, i.e., within the normal physiological range, might result in a lower antibody response to infection and vaccination. We hypothesized, however, that vitamin D is primarily important in establishing immune homeostasis, implying that a relatively high vitamin D status would not hamper an adequate antibody response against pathogens. Our results show that the vitamin D status did not differ between responders and hypo-responders in patients infected with Streptococcus pneumoniae, as well as patients vaccinated against S. pneumoniae, Neisseria meningitidis type C (MenC), and/or Haemophilus influenzae type b (Hib). Furthermore, specific IgG titers were not associated with the vitamin D status in patients vaccinated against S. pneumoniae and MenC, while there was a weak inverse association in Hib-vaccinated patients. These data indicate that a relatively high vitamin D status does not seem to hamper an adequate antibody response upon infection or vaccination, suggesting that vitamin D, in this setting, is not immunosuppressive.