Routine Diagnostic Testing
- Routine serum vitamin D testing or screening for vitamin D deficiency is not recommended.
- Routine serum vitamin D testing during vitamin D supplementation is not recommended.
Population at Risk
The British Columbia (BC) population is at risk of low vitamin D levels from autumn to spring. There is no clinical utility in performing vitamin D tests on patients who are thought to be at risk for sub-optimal vitamin D levels and who would benefit from vitamin D supplementation.
Vitamin D Supplementation without Testing
Because vitamin D supplementation in the general adult population is safe, it is reasonable to advise supplementation without testing. Routine testing of vitamin D levels [25-hydroxyvitamin D or 25(OH)D] is not medically necessary prior to or after starting vitamin D supplementation.
Utilization and Cost of Serum Vitamin D Testing in BC
Utilization of vitamin D testing [as 25-hydroxyvitamin D] in BC has increased ten-fold in the past five years. Medical Service Plan expenditures are approximately $3 million annually for outpatient vitamin D testing with a cost per test of $93.63 in 2009.
Measuring serum vitamin D as 1,25-dihydroxyvitamin D [1,25-(OH)2-D] is seldom indicated, except in selected patients with advanced renal failure, mineral and/or bone diseases. Specialist consultation should be considered for patients with malabsorption, unexplained bone pain, unusual fractures or other evidence suggesting metabolic bone disorder.
Sun Exposure and Vitamin D Synthesis by Skin
The amount of vitamin D produced by the skin is dependent on the surface area exposed, skin pigmentation, age, season, latitude and use of sun block. During winter months in Canada there is insufficient ultraviolet (UV) radiation in sunlight for adequate vitamin D production. Adequate vitamin D can be made in the body during careful exposure of the arms and legs to sunlight for 10-15 minutes per day in the summer months. However, the risk of skin cancer due to sun exposure and tanning beds must be considered.
Dietary Sources of Vitamin D
Vitamin D can be obtained from dietary sources (e.g., salmon, mackerel, tuna, egg yolk), fortified foods (e.g., cow, soy or rice milk), and supplements. There are no plant sources that provide a significant amount of vitamin D naturally. (Refer to the Patient Guide in the original guideline document; see also "Patient Resources" field)
Vitamin D Supplementation
During the Canadian autumn, winter and spring, the adult population is unlikely to achieve adequate vitamin D levels through diet and sunlight only. Consideration should be given to supplementation during those seasons. The two major forms of vitamin D supplements are available as D2 (ergocalciferol) or D3 (cholecalciferol). Vitamin D3 has been shown to be three times more effective than vitamin D2 at increasing serum 25-hydroxyvitamin D levels and maintaining these levels over a longer period of time. As a result, D2 dosage must be tripled to achieve the same benefit.
Osteoporosis Canada recommends supplementing with vitamin D3 over vitamin D2. Most over the counter supplements available in Canada contain vitamin D3 whereas high-dose vitamin D2 is available only by prescription. There is good evidence that supplementation with at least 800 international units (IU) of vitamin D3 per day, combined with calcium, is required to reduce the risk of fragility fractures, therefore 800–1000 IU daily is recommended (although the optimum daily requirement of vitamin D3 is not known). Weekly dosing (one week's adult dose of vitamin D3 taken as a single weekly dose, i.e., 7000 IU) or monthly dosing (one month's adult dose of vitamin D3 taken once a month, i.e., 30,000 IU) may be more convenient for some patients and has been shown to be safe. At this time, high doses of vitamin D3 once a year is not recommended as recent evidence has shown possible increased fracture risk.
Vitamin D Toxicity
Vitamin D toxicity is uncommon. Daily doses of up to 10,000 IU of vitamin D3 for up to five months has not been shown to cause harm in adults. Any harm that would occur from excessive vitamin D ingestion is mediated by hypercalcemia. Therefore, if there is a strong clinical suspicion of vitamin over-use (e.g., patients with eating disorders), then the recommended test is serum calcium (albumin-corrected total calcium* or ionized calcium). Only if the calcium level is elevated would a serum vitamin D measurement be indicated.
*Corrected calcium (Ca) = Ca.measured + (40-alb) X 0.02, [Ca in mmol/L; albumin in g/L]