Vitamin D is a secosteroid hormone essential for maintaining
calcium and phosphate balance, as well as promoting bone health. However, its
roles extend beyond these traditional functions, engaging in complex
interactions with various metabolic processes that have important implications
for global health. Despite the body's ability to produce vitamin D through sun
exposure, deficiency has become a widespread problem affecting people of all
ages and regions. The physiological effects of vitamin D are mediated through
its active form, 1,25-dihydroxyvitamin D [1,25(OH)2D], which binds to the
vitamin D receptor (VDR) found throughout the body. This binding controls the
expression of hundreds of genes involved in cell proliferation,
differentiation, immune response, and inflammation. These mechanisms explain
why vitamin D deficiency is linked to an increased risk of various non-skeletal
diseases, including autoimmune disorders, cardiovascular diseases, cancers, and
infectious diseases. Adding to this complexity is the phenomenon of non-classical
activation. In many extra-renal tissues, such as immune cells, the endothelium,
and the parathyroid gland, 1α-hydroxylase (CYP27B1) is expressed, allowing for
local production of active vitamin D. This enables tissue-specific regulation
independent of the body’s systemic calcium needs. Understanding this
non-classical pathway is especially important for addressing the pathology of
chronic kidney disease (CKD). In patients with CKD, the gradual loss of renal
1α-hydroxylase activity hampers classical vitamin D activation. At the same
time, disruption of local non-classical vitamin D activation in various tissues
has become a key factor in increased inflammation, immune imbalance, and higher
cardiovascular risk in this population. This study offers a comprehensive
review of vitamin D metabolism, covering its synthesis and both classical and
non-classical modes of action. It underscores the serious consequences of
vitamin D deficiency and emphasises the importance of maintaining optimal
levels, particularly for high-risk groups such as those with CKD.
Author(s) Details
Samuel Adinoyi Adavba
Kaduna State University, Kaduna, Nigeria.
Please see the book here :- https://doi.org/10.9734/bpi/aodhr/v7/6482
