Vitamin D and HIV Infection: Immunomodulatory and Extraskeletal Effects. Prevalence, Risk Factors, and Effects of Antiretroviral Therapy

Vitamin D, one of the most ancient hormones from an evolutionary point of view, is a steroidal hormone in its biological active form. Vitamin D deficiency is the most frequently encountered nutritional deficiency and probably is one of the most common medical conditions all over the world. Recent interest in vitamin D has arisen after the discovery of vitamin D receptors (VDRs) in the cells of the immune system (T and B lymphocytes, dendrites and macrophages) and thus its immunomodulatory properties. Epidemiologic data on the relationship between vitamin D and immunity have been published. Some studies have shown vitamin D’s immunomodulatory effect in human immunodeficiency virus (HIV) infection. Low levels of vitamin D have been related to reduced CD4 counts, immune inactivation, anemia, illness progression, and increased mortality. Antiretroviral therapy (ART) for HIV infection impairs vitamin D metabolism, interfering with the hydroxylation needed to activate it or increasing its conversion to 24,25 (OH)2 vitamin D. These effects do not seem to be entirely class dependent because some published reports have described differences between drugs of the same therapeutic group. Several studies have shown that efavirenz increases 25 and 1–25 vitamin D metabolism thereby increasing inactivation of this late, mainly by inducing the 24 hydroxylase enzyme. Some studies have shown that an antiretroviral regimen based on monotherapy with boosted protease inhibitors (PIs) is associated with the lowest risk of vitamin D deficiency.