Exogenous sources of Vit D include;

Exogenously, Vit D can be obtained from the following sources: ^(1,2)

1. Cod liver oil, Trout, Tuna fish, and Salmon
2. Milk, Cheese, and Yoghurt
3. Egg yolk
4. Chicken breast and Beef

Fish liver oils contain the highest quantity of vitamin D among all animal sources.

The FDA has approved UV light-treated mushroom powders as a good source of Vit D2. Other sources include;^(3,4)

1. Soy, Almond, and Oat
2. Fortified Orange juice

Sunlight exposure is the largest source of endogenous Vit D. A study indicates that 1,000IU of Vit D can be produced from 10-15 minutes of sunlight exposure with 22% exposed body. Generally, UVB and UVA exposure accounts for 80-90% of Vit D synthesis. ^(5,6)

Dietary vitamin D is mainly found in the form of vitamin D2(Ergocalciferol) and vitamin D3(Cholecalciferol).

Ergocalciferol is plant-derived, while cholecalciferol is animal-derived; both are absorbed in the intestine. Endogenous Vit D is in the form of cholecalciferol. Cholecalciferol produced due to sun exposure accounts for 80% of the total Vit D. ⁽⁷⁾

Ergo and cholecalciferol are converted into Calcidiol by 25-hydroxylases. Calcidiol is further converted into calcitriol by 1α-hydroxylases. Calcitriol acts on tissues to facilitate specific body processes. ⁽⁸⁾

Vit D2 is synthesized on a commercial level by UV irradiation of ergocalciferol in yeast. On the other hand, D3 is manufactured by UV irradiation of 7-dehydrocholesterol from lanolin procured from sheep wool.

Vit D injection and supplements are manufactured through this process. Vit D3 can also be prepared by UV irradiation of lichen. ^(9,10)

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According to a report, ∼1 billion people worldwide have vitamin D deficiency. This colossal figure suggests that awareness of the benefits of vitamin D is critical. A Vit D deficient individual might have the following signs/symptoms ^{(11,12,13,14,15)}

1. Rickets(in children)
2. Osteomalacia(in adults)
3. Osteoporosis(weak and porous bones)
4. Impaired bone growth and bone pain
5. Joint deformities
6. Muscle weakness and pain
7. Fatigue

The following factors can lead to Vit D deficiency ^(16,17)

1. Low sunlight exposure
2. Malnutrition or undernutrition
3. Dark skin
4. Age>65 years
5. Medical conditions, i.e. CKD, CLD, Cystic fibrosis, IBD, and Obesity.
6. Drug interaction while taking steroids, anti-TB, and anti-hyperlipidemic drugs.

S-25 Hydroxy Vit D(25(OH)D) is the diagnostic test to rule out vitamin D deficiency. The half-life of blood circulating 25(OH)D is around 15 days. Ranges are mentioned as follows: ⁽¹⁸⁾

The Institute of Medicine, Food, and Nutrition Board recommends DRA of vitamin D up to 400IU in children(less than 1 year) and up to 600IU in adults(up to 70 years). ⁽¹⁹⁾

Vit D Injections come in various dosage ampoules. You can choose the injection strength correlating with lab results.

A single ampoule may minimally contain 50,000IU, and strength increases to even 6,00,000IU. FDA recommends a Vit D fortified diet as per the DRA.⁽²⁰⁾

Patients suffering from osteoporosis and reduced bone density are usually advised to take Vit D ampoule P/O or I/M weekly, depending on Vit D deficiency.

Vit D injections come in a variety of doses and they can be taken orally, the easiest route of administration. Other benefits of Vit D injection include;

• Bone strengthening⁽²¹⁾
• Boosting immunity⁽²²⁾
• Assist in weight loss⁽²³⁾
• Improve mood⁽²⁴⁾

Excess sun exposure does not cause vitamin D toxicity. However, toxicity can occur due to excessive supplement intake. Due to toxicity, an individual might experience ⁽²⁵⁾

• Polydipsia(increased thirst)
• Constipation
• Nausea
• Confusion
• Dysarthria

Consulation from a registered physician should be sought before using Vit D injections.

1. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC3941824/
3. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC3651966/
5. https://www.sciencedirect.com/topics/veterinary-science-and-veterinary-medicine/vitamin-d
6. https://pubmed.ncbi.nlm.nih.gov/30992519/#:~:text=Daily%20solar%20UV%20exposure%20durations,and%20winter%20months%20in%20Switzerland.
7. https://www.researchgate.net/figure/Metabolism-of-vitamin-D-a-Endogenous-synthesis-vitamin-D-is-80-synthesized-in-the_fig2_347765398
8. https://www.researchgate.net/figure/Schematic-illustration-vitamin-D-synthesis-pathway-and-signalling-mechanisms-relevant-to_fig1_336255216
9. https://www.sciencedirect.com/science/article/abs/pii/B978012381978910006X
10. https://www.researchgate.net/figure/Synthesis-and-activation-of-vitamin-D-Vitamin-D3-is-synthesized-in-the-skin-upon-UVB_fig1_236959412
11. https://pubmed.ncbi.nlm.nih.gov/29265106/
12. https://www.ncbi.nlm.nih.gov/books/NBK551616/
13. https://www.webmd.com/diet/vitamin-d-deficiency
14. https://my.clevelandclinic.org/health/diseases/15050-vitamin-d-vitamin-d-deficiency
15. https://pmc.ncbi.nlm.nih.gov/articles/PMC4018438/
16. https://www.webmd.com/diet/vitamin-d-deficiency
17. https://emedicine.medscape.com/article/128762-overview
18. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
19. https://nap.nationalacademies.org/resource/13050/Vitamin-D-and-Calcium-2010-Report-Brief.pdf
20. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/#en1
21. https://pmc.ncbi.nlm.nih.gov/articles/PMC3257679/
22. https://pmc.ncbi.nlm.nih.gov/articles/PMC3166406/
23. https://pmc.ncbi.nlm.nih.gov/articles/PMC6071442/
24. https://www.sciencedirect.com/science/article/pii/S1087079220301222
25. https://my.clevelandclinic.org/health/diseases/15050-vitamin-d-vitamin-d-deficiency#symptoms-and-causes