Vitamin D has two forms, namely ergocalciferol which is derived from ergosterol in plants, usually yeast, by irradiation, and cholecalciferol which is usually derived from fish, or from the irradiation of 7-dehydrocholesterol from lanolin, or by chemically converting cholesterol.
Some research shows that vitamin D3 is somewhat more effective at higher doses in boosting the concentrations of vitamin D prohormone in the body, and it is usually used nowadays to fortify milk and milk products, as well as to prepare supplements.
The normal supplementation dosage ranges from 400 IU/ mL to 400 IU/drop. Care must be enjoined and demonstrated to avoid overdosage, especially with the higher concentration, in infants. However, some current research indicates that 800-5000 IU/day improves musculoskeletal health in the elderly, preventing up to 50% of falls.
In those who have vitamin D deficiency, up to 600000 IU administered in several divided doses over a few weeks, such as 50000 IU/week for 8 weeks. This is sufficient to bring the tissue and serum levels back to normal. Following this, 800-1000 IU may be taken daily, either from dietary sources or as a supplement.
Most people maintain a normal vitamin D concentration provided they get 10-15 minutes of sunlight a day on exposed skin. In such a case, supplements are not usually necessary. Indications for vitamin D supplements should be based on measurement of 25-hydroxy-D levels.
Vitamin D supplements may interact with various medications. These include:
- Steroids – corticosteroids like prednisone, which are widely prescribed for their anti-inflammatory actions, also reduce calcium absorption as well as reduce the metabolism of vitamin D, exacerbating bone loss and speeding up the development of osteoporosis with long-term use.
- Cholesterol-lowering agents such as cholestyramine can impair the absorption of vitamin D as well as other fat-soluble vitamins by interfering with fat absorption.
- Anticonvulsants – phenytoin and phenobarbital both induce the hepatic metabolism of vitamin D, leading to increased inactivation, which leads to lower calcium absorption.