All you need to know about vitamin D and its role in bone health.

What is vitamin D?

Vitamin D (also referred to as “calciferol”) is a fat-soluble vitamin. It is also known as ‘Antirachitic vitamin due to its ability to prevent rickets (a condition that affects bone development in children) and osteomalacia (softening of your bones) in adults.Vitamin D can be derived from either endogenous synthesis in the skin or from the diet, because our body can synthesise vitamin D naturally by sun exposure. Due to this reason, it is sometimes referred to as prohormone. 

How vitamin D synthesis in skin?

Vitamin D3 is synthesised from the sterol 7-dehydrocholesterol (a compound present in skin) by a process involving UVB light in the wavelengths 290 to 315 nm. UV irradiation opens the 9,10-bond of the provitamin to give a previtamin D3 intermediate in the upper layers of the skin before it is isomerized non enzymatically by heat to give vitamin D3 in the lower layers.

How many forms of vitamin D are there? 

Vitamin D mainly has two forms, namely:

  • Vitamin D2 (Ergocalciferol) 
  • Vitamin D3 (Cholecalciferol)

What are the dietary sources of vitamin D? 

Unfortunately, the dietary sources of vitamin D are few, and most foodstuffs are devoid of vitamin D. The only significant sources of vitamin D (D2 or D3) are following:

Non-Vegetarian Sources:

  • Animal liver
  • Fatty fish (e.g. salmon, halibut, cod)
  • Egg yolks
  • Fish oils (cod liver oil)

    Vegetarian Sources

    • For vegetarian sun dried Shiitake mushrooms and Chlorella are good sources of vitamin D2.
    • Lichen (algae or cyanobacteria) is the only dietary source of vitamin D3 for vegetarians which is mainly used in vegetarian dietary supplements to provide vitamin D3

    What is the role of vitamin D in our body?

    • Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal bone mineralization and to prevent hypocalcemic tetany (involuntary contraction of muscles, leading to cramps and spasms)
    • It is also needed for bone growth and bone remodelling by osteoblasts and osteoclasts (Bone cells). Without sufficient vitamin D, bones can become thin, brittle, or misshapen.
    • Sufficient vitamin D prevents rickets in children and osteomalacia in adults. Together with calcium, vitamin D also helps protect older adults from osteoporosis.
    • Other roles of vitamin D in the body includes reduction of inflammation as well as modulation of processes like cell growth, neuromuscular and immune function, and glucose metabolism.
    • Many genes encoding proteins that regulate cell proliferation, differentiation, and apoptosis are modulated in part by vitamin D.

    What are the symptoms of Vitamin D deficiency?

    • Fatigue and tiredness
    • Bone and back pain
    • Poor immune health (frequent cases of infection such as the flu and respiratory infections)
    • Depression & anxiety 
    • Poor wound healing 
    • Hair loss
    • Bone loss
    • Muscle pain

    How to diagnose vitamin D deficiency?

    Deficiency of vitamin D is called Hypervitaminosis D. Vitamin D sufficiency or deficiency is evaluated by a blood test which measures your serum 25-hydroxyvitamin D.

    Reference ranges of serum Vitamin D (25-OH Vitamin D) levels are:

    Vitamin D Status 

    Vitamin D 25 HYDROXY (ng/ml)










    How much vitamin D a person needs per day? 

    RDA* or Recommended Dietary Allowance are proposed by NIN & ICMR for Indians.

    These recommendations help us to know how much vitamin D should be taken in our daily diet to prevent insufficiency or deficiency. Let us check the ranges in details below:

    Age Group 

      RDA (per day/ IU)
    Women (Non pregnant, Non lactating) 
    • Pregnancy 
    • Lactation 
    • 0-6 months
    • 6-12 months
    • 1-9 years (Boys & Girls)
    • 10-18 years  (Boys & Girls)
    Old age 
    ≥ 60 years (Men and women)
    *RDA- Means Recommended Dietary Allowance per day as per an individual’s age group. 

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