Vitamin D

Vitamin D is made from sunlight acting on the skin. Vitamin D deficiency is mainly caused due to a lack of exposure to sunlight and can cause muscle weakness and bone defects. People that have dark skin or certain medical conditions or medications that affect vitamin D metabolism can also develop vitamin D deficiency (5).

Vitamin D3 is mainly given by itself for vitamin D deficiency. It can also be given with calcium and other drugs for osteoporosis or rickets to prevent bone loss and weakening (1, 2, 5, 6, 7). Recommended daily intake of vitamin D is 600 IU (or 800 IU for those aged 70+) (1, 6).

Foods that are a good source of vitamin D include dairy products, eggs and fatty fish (6, 7).

More about Vitamin D

Vitamin D3, also known as cholecalciferol, is a fat soluble vitamin. When sunlight’s UVB radiation acts on 7-dehydrocholesterol in the skin, vitamin D3 is formed. Vitamin D3 itself is biologically inactive and it undergoes a series of transformations, first to 25-hydroxyvitamin D (calcifediol) in the liver and then to 1,25-dihydroxyvitamin D (calcitriol – the active form of vitamin D) in the kidneys (5, 6). Calcitriol helps the body absorb calcium and phosphate and also helps with bone mineralisation (5).

Avoid taking other products that also contain vitamin D when taking vitamin D3. Vitamin D3 is usually well-tolerated and has no risk of toxicity at normal doses, but high levels of vitamin D can cause hypercalcaemia which may present with nausea, vomiting, constipation, headache, thirst, muscle weakness amongst other symptoms. Vitamin D toxicity may also cause anaemia (1, 2, 6).

Certain medications can affect vitamin D absorption. Check with your doctor or pharmacist on when to take these medications in between vitamin D3 doses.

It is advised that people with severe kidney dysfunction avoid the use of vitamin D supplement and see their doctor (1).

Information for prescribers

Vitamin D can be formulated into liquids, capsules and injections.

We can formulate liquids from 400IU/mL to 100 000 IU/mL.

Capsules are generally made in weekly dosages or monthly dosage of up to 50 000 IU per capsules. In practice we have found higher doses of Vitamin D dosed either weekly or monthly aid with patient compliance.

Dosage guidelines

For adults with mild vitamin D deficiency: 1000-2000 IU daily or 7000-14000 IU weekly (5)

For adults with moderate to severe vitamin D deficiency: 3000-5000 IU daily for 6-12 weeks then 1000-2000 IU daily (1, 5)

For children with moderate to severe vitamin D deficiency that may cause rickets:

Neonates (< 1 month old): 1000 IU daily for 3 months

Children aged 1-12 months: 3000 IU daily for 3 months

Children aged > 12 months: 5000 IU daily for 3 months or 150000 IU single dose that may be repeated every 4-6 weeks if needed

Long-term maintenance dose of 400 IU daily (1, 3)

For osteoporosis: supplement to maintain serum 25-hydroxyvitamin D (calcifediol) > 50 nmol/L (4)

References

(1) AMH 2019, Colecalciferol, Australian Medicines Handbook

(2) Royal Pharmaceutical Society 2019, Vitamin D Substances, Martindale: The Complete Drug Reference

(3) Therapeutic Guidelines 2019a, Osteomalacia and rickets, eTG June 2019 edition

(4) Therapeutic Guidelines 2019b, Osteoporosis and minimal-trauma fracture, eTG June 2019 edition

(5) Therapeutic Guidelines 2019c, Vitamin D deficiency, eTG June 2019 edition

(6) Therapeutic Research Centre 2019, Vitamin D, Natural Medicines

(7) WebMD n.d., Cholecalciferol (Vitamin D3) Oral : Uses, Side Effects, Interactions, Pictures, Warnings & Dosing, WebMD, https://www.webmd.com/drugs/2/drug-6152/cholecalciferol-vitamin-d3-oral/details