Among environmental factors related to pathogen infection, vitamin D is largely considered to
be protective and promoter of good health. For these reasons, a general concern exists about vitamin D
insufficiency that has been found around world reaching epidemic dimensions. In the last few years,
interest about the role of vitamin D on immune response has been increased after encouraging data
illustrated the well-known contribution of the binomial sunlight exposure/vitamin D on protection to
mycobacterium infections. The vitamin D mediated induction of microbicide factors against bacterial
infections runs in parallel with the vitamin D immunosuppressant activity induced to control the
exacerbation of the cellular immune response. These complementary effects can be modulated to
guarantee a correct vitamin D action. Concerning HIV infection a protective role can be expected from the
vitamin D mediated microbicide activity, but no single effects can be deduced from the vitamin D
immunosuppressant activity. In addition, the direct effects of vitamin D by promoting HIV replication can
act as a confounding factor when trying to understand the role of vitamin D in HIV infection. In the
present review we have evaluated available bibliography of vitamin D action on the immune system
response crossing it with data on HIV immunopathology trying to find common pathways that can shed
light on the role of vitamin D on HIV infection and disease progression to AIDS.
