Vitamin D Deficiency in Quebec: Why It's So Common (and How to Fix It)
In Quebec latitudes, your skin makes almost no vitamin D from November to March. That's why so many of our patients test low — and it's a fixable problem.
Why deficiency is so common here
Montreal sits at latitude 45°N. From roughly November to March, the sun's angle is too low for UVB to produce meaningful vitamin D in exposed skin. Add long winters spent indoors, sunscreen use in summer, darker skin tones which naturally produce less D from the same sun, and older age (which reduces skin synthesis capacity) — and the deficiency rate is not surprising.
Testing and dosing
A serum 25-hydroxyvitamin D level is the standard test. Sufficiency is usually defined as > 75 nmol/L; deficiency < 50 nmol/L; severe deficiency < 30 nmol/L.
For most adults, 1000–2000 IU/day of vitamin D3 (cholecalciferol) is a reasonable maintenance dose. Correction of documented deficiency typically uses higher doses (4000–5000 IU/day) for 8–12 weeks, then retest and drop to maintenance. Extremely high one-off doses are usually not necessary and can cause fluctuations.
Frequently asked questions
Do I need a prescription for vitamin D?+
No — over-the-counter vitamin D3 is widely available. A consultation and blood test still help you know what dose is right and confirm you've corrected the deficiency.