
Introduction
Vitamin D is either synthesised in the skin through exposure to ultraviolet B rays in sunlight, or ingested as a dietary vitamin D. [3]
The version made in the skin is referred to as vitamin d3 whereas the dietary form can either be D3 or a plant-origin molecule, D2. [5]
The 2 forms available through diet or supplements are Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Both forms are well absorbed in the small intestine.
Neither ageing nor obesity alters vitamin-D absorption from the gut. [1] However, older people are at high risk of vitamin D deficiency due to age and people with darker skin are less able to produce vitamin D from sunlight. [1]
More than 90% of vitamin D for most people comes from exposure to sunlight. [9]
Body Functions

Recommended Daily Intake

Deficiency Symptoms

Vitamin D Food Sources

Excessive Intake/ Toxicity Side Effects

Groups At Risk of Vitamin D Deficiency
Vitamin D Interaction With Other Nutrients
- Dietary fat – Presence of fat in the gut enhances vitamin D absorption, but some vitamin D is absorbed even without dietary fat. [1]
- Magnesium – Magnesium regulates the activity of critical enzymes in vitamin D metabolism and hence, magnesium deficiency negatively affects vitamin D status. [3,6]
- Calcium – Vitamin D increases calcium absorption in the gastrointestinal tract. It is believed that without enough vitamin D in the body, only 10% to 15% of dietary calcium is absorbed, compared to 30% to 40% absorption when vitamin D reserves are normal. [8]
- Phosphorous – Vitamin D helps phosphorus absorption and retention, thereby helping maintain normal serum levels of these minerals [1,2]
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