Vitamin D Deficiency and Resistance in Long- Term Illnesses

The identification of the role of vitamin D in the human body has evolved drastically over the years. Now considered an essential vitamin, D was previously labelled as a hormone. The synthesis is initiated within the keratinocytes due to the sunlight exposure and is transformed into an active form through a series of reactions in the liver and kidney, where the enzymes required for this conversion are present. As a result of restricted production or availability, vitamin D deficiency is a concerning issue in children and adults. Along with this, certain genetic, molecular and metabolic disturbances result in the development of vitamin D resistance. The role of pathogens and environmental toxins that result in this condition is also asserted. The review also explores the mechanism of vitamin D resistance in chronic diseases, such as the reduced enzyme activity due to a variety of factors, leading to chronic kidney disease. Impaired hydroxylation in the liver contributes to chronic lung disease, and how obesity, endocrine, and inflammatory disorders impact this mechanism is also acknowledged. The clinical consequences of vitamin D dysfunction are wide, such as effects on bone, teeth and even muscles. It also plays a role in the pathogenesis of Multiple Sclerosis and may lead to associated symptoms. The review also discusses the diagnostic methods, which mainly focus on clinical and biochemical studies. The management and therapeutic strategies that underlie the importance of vitamin D supplementation and the use of enzyme analogues and symptomatic management.