Vitamin D is a fat-soluble vitamin that plays a critical role in various body processes. Here's an overview:

Functions of Vitamin D

1. Bone Health: Vitamin D promotes calcium absorption in the gut, which is essential for maintaining healthy bones and teeth¹². Insufficient vitamin D can lead to bone diseases such as osteoporosis and rickets³.
2. Immune System: It supports the immune system in combating pathogens².
3. Muscle Function: Vitamin D is vital for muscle function as it helps muscles move².
4. Nervous System: It aids in the functioning of the nervous system by helping nerves carry messages between the brain and the body².

Sources of Vitamin D

1. Sunlight: The skin synthesizes vitamin D upon exposure to sunlight⁴. However, excessive sun exposure can lead to skin aging and skin cancer⁴.
2. Food: Few foods naturally contain vitamin D. These include:
   • Oily fish (e.g., salmon, mackerel)⁵
   • Red meat⁵
   • Egg yolks⁵
   • Fortified foods (e.g., milk, cereals)⁶
3. Supplements: Vitamin D supplements are available in two forms: D2 (ergocalciferol) and D3 (cholecalciferol). Both effectively increase vitamin D levels, but D3 might maintain higher levels for longer⁶⁷.

Recommended Intake

The recommended daily allowance (RDA) for vitamin D is:

• 600 IU (15 mcg) for adults between 19-70 years
• 800 IU (20 mcg) for adults older than 70 years⁷

Deficiency and Excess

• Deficiency: Deficiency can lead to conditions like osteomalacia in adults and rickets in children¹². Long-term deficiency can also lead to osteoporosis¹.
• Excess: Excessive vitamin D can cause health issues, though the exact adverse effects are still being studied⁵.

Footnotes

1. https://www.medlineplus.gov/vitamind.html ↩ ↩² ↩³

2. https://www.mayoclinic.org/drugs-supplements-vitamin-d/art-20363792 ↩ ↩² ↩³ ↩⁴ ↩⁵

3. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/ ↩

4. https://www.bhf.org.uk/informationsupport/heart-matters-magazine/nutrition/ask-the-expert/foods-high-in-vitamin-d ↩ ↩²

5. https://ods.od.nih.gov/factsheets/VitaminD-Consumer/ ↩ ↩² ↩³ ↩⁴

6. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/ ↩ ↩²

7. https://nutritionsource.hsph.harvard.edu/vitamin-d/ ↩ ↩²