Vitamin d in physiological and pathological conditions

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Recent Trends in Biochemistry
incidence of breast cancer. Low levels of 25-hydroxy vitamin D 
may be attributed to faster progression of breast cancer. More-
over, mortality rates of perimenopausal ovarian cancer have 
also been found lower in sunny regions. The same effect can be 
seen in case of prostate cancer. In a study of 19000 men, those 
with levels of 25-hydroxyvitamin D <16ng/mL had a higher in-
cidence of prostate cancer than those having more than this 
value. Although, there are few studies showing no association 
between vitamin D and cancer, making the topic controversial 
[12,13].
We know that vitamin D is involved in regulation of cellular 
proliferation and maturation. Nevertheless, the exact mecha-
nism is not fully understood. A number of genes controlling 
proliferation, differentiation, apoptosis and angiogenesis, are 
directly or indirectly affected by vitamin D. The active form of 
the latter increases inhibitors and decreased activators of cy-
clin-cyclin dependent kinase complexes in addition to increas-
ing levels of cyclin dependent kinase inhibitors Cip/Kip proteins 
P21 and P27. These proteins are known to keep the cell cycle 
in the G1/S phase, preventing DNA synthesis and so, the cell 
proliferation [12].
Vitamin D and autoimmune diseases
Vitamin D is known to have important immunomodulatory 
effects in body. Dendritic cells are primary targets for this activ-
ity of 1,25-dihydroxycholecalciferol, the active form of vitamin 
D. It is indicated by inhibited dendritic cells differentiation and 
maturation leading to down regulated expression of MHC-II, 
co-stimulatory molecules like CD40, CD80, CD86 and decreased 
production of IL-12. Besides these, 1,25-dihydroxycholecalcifer-
ol increases IL-10 production and thereby, promotes dendritic 
cell apoptosis. In this way, vitamin D inhibits dendritic cell de-
pendent T-cell activation. Apart from these, vitamin D receptor 
agonists seem to inhibit pathogenic pro-inflammatory T-cells 
like Th1 and Th17 and under appropriate conditions they tend 
to favor a deviation to Th2 pathway [14].
These types of immunomodulatory and anti-inflammatory 
effects are particularly efficient for the rheumatoid arthritis pa-
tients to support a therapeutic role of 1,25-dihydroxycholecal-
ciferol in this disease. From different studies, it is also seen that 
vitamin D may play an important role in maintenance of B-cell 
homeostasis and correction of vitamin D deficient state may af-
fect the treatment of B-cell mediated autoimmune disorders 
such as systemic lupus erythematosus (SLE) [14].