**8. Effect of vitamin D on mood and cognition**

Vitamin D receptors and the 1α-hydroxylase enzyme have been isolated and found in the regions of the cerebral cortex and cerebellum, suggesting the conversion of calcifediol into an active form of vitamin D, i.e., calcitriol in the brain for a local cellular response [3, 18]. Several studies discuss the deficiency of vitamin D in the body at its targeted ligand binding sites due to less sunlight exposure or sun blockage, vitamin D receptor mutation causing phenotypic-conformational changes at the ligand binding site, and insufficient vitamin D-fortified diet, all causing major or minor mood disorders and illustrate the effectiveness of vitamin D or sunlight therapy (phototherapy), gene therapy, or supplemented vitamin D diet therapy for the treatment of depression and other mood disorders, demonstrating the associations between 25(OH) vitamin D concentrations and mood alone or mood and cognition in adults of all ages, including pregnant women, older adults, and targeted vitamin D-deficient population globally [3, 10].
