Vitamin D is a fat-soluble vitamin that functions as a hormone in the body.
It is produced when skin is exposed to UVB radiation and can also be obtained from dietary sources such as eggs, oily fish, and mushrooms, although dietary intake is often insufficient. Approximately one in four Australian adults have a vitamin D deficiency.
Health Consequences of Deficiency
Vitamin D promotes calcium absorption, which is essential for bone health. Deficiency can lead to specific health conditions:
- In children: Rickets, characterized by soft bones, delayed growth, and skeletal deformities.
- In adults: Osteomalacia, causing bone pain, tenderness, and an increased risk of fractures.
- Long-term: Osteoporosis, muscle weakness, and an increased susceptibility to respiratory infections.
Causes of Deficiency
Several factors can contribute to vitamin D deficiency:
- Insufficient sunlight exposure: This can result from an indoor lifestyle, night shift work, or living in high-latitude regions such as Tasmania.
- Skin pigmentation: Darker skin pigmentation reduces the skin's ability to produce vitamin D.
- Skin conditions: Disorders such as psoriasis or severe burns can impair vitamin D production.
- Seasonal variation: Low sunlight during winter months, particularly in southern regions, can increase deficiency risk.
Types of Supplements Available in Australia
The following supplements are available for treating or preventing deficiency:
- Low-dose Vitamin D3 (20 µg): Available over the counter for daily use.
- High-dose Vitamin D3 (175 µg): Available for weekly use; requires a pharmacist consultation.
- Calcitriol (0.25 µg): The active form of vitamin D, available only by prescription, used to treat hypocalcemia in patients with chronic kidney disease.
- Combination products: Vitamin D3 is also found in multivitamins and in supplements combined with calcium or vitamin K.
Safety and Interactions
- Upper tolerable intake: 100 µg per day. Prolonged intake of more than 100 µg daily can cause hypercalcemia, which may lead to nausea, vomiting, muscle weakness, and kidney stones.
- Sun exposure: Sun exposure does not cause vitamin D toxicity but does increase the risk of skin cancer.
- Potential drug interactions: Vitamin D supplements may interact with statins, orlistat, steroids, and thiazide diuretics.
Recommendations
- Sunlight exposure: Most people require 5 to 30 minutes of direct sunlight several times per week to maintain adequate vitamin D levels.
- Supplementation: Supplements are generally not needed unless sunlight exposure is insufficient or a relevant skin condition is present.
- Testing: A blood test, conducted by a general practitioner or using a Therapeutic Goods Administration (TGA)-approved home test, can confirm a deficiency.
- Consultation: Individuals should consult a pharmacist or healthcare professional for guidance on the appropriate product and dosage if a deficiency is confirmed.