25-hydroxyvitamin D from a simple blood spot collection.
A 2010 study estimated that 37,000 deaths could be prevented every year if the Canadian average vitamin D level* was 105 nmol/L. Grant WB
*measured as 25-hydroxyvitamin D3, the standard test for vitamin D sufficiency.
When to Test?
Ideally you want to know what your vitamin D level is after sun exposure, and after little or no sun exposure.
Many experts recommend testing twice a year – at the end of winter (March) for the lowest levels, and again at the end of August to see levels at their highest. If you supplement with vitamin D, any time of year is a good time to test, but if you have recently changed your dose of vitamin D, wait at least 4 weeks before testing.
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