Vitamin D

Introduction

Vitamin D is a fat-soluble vitamin, known for its antirachitic activity. Calciferols are a group of lipid-soluble compounds with a 4-ringed cholesterol backbone and refer to both, Vitamin D3, i.e., cholecalciferol and Vitamin D2, i.e., ergocalciferol. Vitamin D, in general, refers to Vitamin D3. Vitamin D can be synthesized endogenously. About 90% of the required Vitamin D is synthesized in the skin under sun exposure. It is needed for the maintenance of normal blood levels of calcium and phosphate that are required for normal mineralization of bone, muscle contraction, nerve conduction, and general cellular function in all cells of the body. It is also found to be important for immune function, for inflammation, cell proliferation, and differentiation.1

The active form of Vitamin D stimulates the absorption of calcium in the duodenum and increases calcium influx in distal tubules of kidney through nuclear Vitamin D receptor (VDR); latter is specifically regulated by parathormone level.1

Magnitude of Vitamin D Deficiency in India

The prevalence of Vitamin D deficiency is reported worldwide, both in sunshine deficient and sunshine sufficient countries. Still, it is the most underdiagnosed and undertreated nutritional deficiency in the world. However, various studies showed poor Vitamin D status irrespective of age, sex, and geography.1

As there is no standard guideline which is followed all over the world for classifying the Vitamin D status, these studies had different cutoff values for the deficiency. The vast majority of these studies used serum 25(OH) D level of < 20 ng/mL as Vitamin D deficiency. The community-based Indian studies of the past decade done on apparently healthy controls reported a prevalence ranging from 50 to 94%, except for one study which reported a prevalence of 34.5% which can be due to the low cutoff. These studies which included various age groups reflect the magnitude of the problem. High prevalence was seen throughout the country. Hospital-based studies showed a prevalence of Vitamin D deficiency ranging from 37 to 99%.1

Sources of Vitamin D3

The major source of Vitamin D is the endogenous synthesis in skin on exposure to sunlight, namely, ultraviolet B (UV‑B) radiation of wavelength 290–320 nm. Main dietary sources are fish, fortified food, and supplements. Vegetables and grains are poor sources. Synthesis of vitamin in skin on exposure to UV‑B is also affected by latitude, solar zenith angle, atmospheric pollution, ozone layer, and melanin pigmentation.1

Recommended intake of Vitamin D

The amount of vitamin D intake depends on age. Average daily recommended amounts are listed below in micrograms (mcg) and International Units (IU):2

Life Stage
Recommended Amount
Birth to 12 months
10 mcg (400 IU)
Children 1–13 years
15 mcg (600 IU)
Teens 14–18 years
15 mcg (600 IU)
Adults 19–70 years
15 mcg (600 IU)
Adults 71 years and older
20 mcg (400 IU)
Pregnant and breastfeeding women
15 mcg (600 IU)

Vitamin D and health

The major biological function of Vitamin D is to maintain normal blood levels of calcium and phosphorus. Vitamin D aids in the absorption of calcium, helping to form and maintain strong bones. Recent research also suggests that sufficient intake of this fat-soluble vitamin may provide protection from and decrease an individual’s risk of developing osteoporosis, hypertension, cancer, and several autoimmune diseases. Studies report that it triggers the body’s immune cells to produce antibodies; therefore, Vitamin D promotes an overall increase in the strength of the immune system. To date, more than 500 studies support the role of Vitamin D in immune health. Results from some studies report that Vitamin D assists in the maintenance of joint and muscle comfort, as well as the maintenance of a healthy mood, and supports breast, colon and prostate health.3

References:
  1. Aparna P, Muthathal S, Nongkynrih B, et al. Vitamin D deficiency in India. J Family Med Prim Care. 2018;7:324–330.
  2. Vitamin D. Available at ods.od.nih.gov/factsheets. Accessed on October 10, 2020.
  3. The important role of vitamin D. Available at www.pharmacytimes.com/publications/. Accessed on October 10, 2020.