Vitamins are micro-nutrients needed by the body for maintaining good health. There are two major types of vitamins, that is fat-soluble vitamins and water-soluble vitamins. Vitamin B complex and C are water-soluble while vitamins A,D, E and K are fat-soluble. Vitamin D includes many subfamilies, however from clinical perspective, estimation of VITD2 and VITD3 is most important. Vitamin D2, also known as ergocalciferol, is synthesized by plants, fungi and bacteria, while vitamin D3, also known as cholecalciferol is formed in animals. Vitamin D3 is generally present at higher concentrations in the human body, and it is the major contributor of total vitamin D levels in human serum. Vitamin D3 is synthesized in humans on exposure of skin to sunlight. Many routinely consumed food products are considered as rich sources of vitamin D3 like milk, fish, egg and cod liver oil. Vitamin D3 is also more efficacious as compared to vitamin D2, because it binds to vitamin D receptors (VDR) with very high affinity.
For routine lab tests, estimation of 25-OH vitamin D (Total) is preferred to that of 1,25 (OH)2 vitamin D3 due to three obvious reasons:
25-OH vitamin D has the highest concentration in the body among all vitamin D metabolites.
Its levels remain stable for almost two weeks.
Vitamin D toxicity arises due to excess levels of 25-OH vitamin D rather than 1,25 (OH)2 vitamin D3.
Vitamin D3 is the most biologically active form of vitamin D.
Vitamin D is important for maintenance of bone health and its deficiency can lead to rickets or osteomalacia. Deficiency of vitamin D has also been linked to depression, obesity, rheumatoid arthritis and cancer. Vitamin D plays an important role in prevention of osteoporosis, helps in lowering of blood pressure in people with hypertension, lowers the risk of disorders like cardiovascular disorders, type 2 diabetes, allergies and dental cavities.
Although vitamin D deficiency can be treated and overcome with the help of supplements, an overdose of the same can lead to toxicity. Toxicity can result in hypercalcemia characterized by symptoms like thirst & urination, nausea, dizziness and headaches.