Vitamin D is a fat-soluble vitamin and has two primary forms: cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2). Cholecalciferol has a 10-fold increased potency as compared to ergocalciferol.3 Furthermore, it induces a quicker response in the production of serum calcidiol that sustains longer at higher concentrations. Various foods are fortified with vitamin D, including milk and cereal. Other dietary sources include fish liver oils, fatty fish, and eggs from hens that have been supplemented with vitamin D.
Cholecalciferol is synthesized by the skin after exposure to sunlight. In healthy individuals, 7-dehydrocholesterol in the skin is converted to cholecalciferol. Brief exposure of approximately 20% of body surface area to sunlight is equivalent to ingesting 200 IU of cholecalciferol. Thus, cutaneous production is highly efficient. However, many individuals lack the ability to efficiently produce adequate stores of cholecalciferol. Therefore, cholecalciferol supplementation is essential.
The chemical structure differences between the two forms of vitamin D do not affect the metabolism or clinical responses once activated within the body. Although animal experiments have indicated a difference in toxicity between vitamin D3 and vitamin D2, human studies have been inconclusive.2 Vitamin D is responsible for appropriate calcium and phosphate balance and is required for normal bone growth and mineralization. Patient specific dosing can be determined by measuring 25-hydroxyvitamin D [25(OH)D] serum concentrations, which represent all sources of vitamin D (e.g., sunlight and dietary or from supplements). Although cholecalciferol is labeled for use in several disease states, the primary use is now for vitamin D supplementation and the prevention and treatment of vitamin D deficiency and rickets.
NOTE: In the US, nutraceuticals are marketed under the Dietary Supplement and Health Education Act of 1994 (DSHEA). Consequently, nutraceuticals are not regulated under the same restrictions as pharmaceuticals; scientific data supporting claimed benefit(s) are not always available for nutraceuticals. Consumers should also note that rigid quality control standards are not required for nutraceuticals, and substantial variability can occur in both the potency and the purity of these products.