Vitamin D Blood Level Test

In Canada, a lack of direct sunlight in winter means we do not make vitamin D from October to April. Only about 1/3 of Canadians have vitamin D levels* above 75 nmol/L, the minimum considered optimal for health. Health Canada. 15 minutes of direct sunlight on exposed skin twice a week provides enough vitamin D for the body's needs.

Causes of Vitamin D Deficiency

Season or Latitude
The low angle of the sun in Canada means we cannot make vitamin D during the winter months.

Sunscreen Use
SPF 15 sunscreen reduces D synthesis by 99%.

Skin Colour
Dark skin has more of the pigment melanin, which can reduce vitamin D synthesis by up to 99%.

Age
Vitamin D synthesis decreases by about 75% in a 70 year old.

Medications
Specific medications, like anti-rejection, anti-seizure and AIDS medicines can speed up the breakdown of vitamin D, resulting in low levels of 25-hydroxyvitamin D.

Cholesterol-lowering medications are commonly prescribed for high cholesterol and heart disease. Monitoring cholesterol is important, because having too-low cholesterol impairs the body's ability to make vitamin D.

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.