Canada sits far enough north that from roughly October to March, the sun is at too low an angle for your skin to produce meaningful vitamin D at all. That's a fact of geometry, not lifestyle.
What it does
Vitamin D governs how you absorb calcium and phosphorus, which makes it central to bone health. It's also involved in normal immune function and muscle function. Receptors for it turn up all over the body, which is why it's so heavily researched — and why the claims made about it often run ahead of the evidence.
The latitude problem
Your skin makes vitamin D when UVB light hits it. Above roughly the 37th parallel — which is all of Canada — UVB is too weak through the winter months for that reaction to happen meaningfully, no matter how long you stand outside.
Add to that: sunscreen blocks the reaction (correctly — skin cancer risk is real and not worth trading), darker skin needs considerably longer exposure, glass blocks UVB entirely, and older skin produces less.
Food sources are limited
Oily fish is the best real source — salmon, mackerel, sardines, herring. Egg yolks contribute a little. Fortified milk and plant milks contribute a little. Mushrooms exposed to UV light produce D2, and you can do this at home by laying them gills-up in sunlight for a few hours, though D2 appears less effective than D3 at maintaining blood levels.
Realistically, food alone rarely covers it through a Canadian winter.
What I'd actually do
Get tested. A blood test for 25-hydroxyvitamin D tells you where you stand, and it removes all the guesswork. Your doctor can order it — note that in some provinces it isn't covered unless there's a clinical reason, so ask.
Dose depends entirely on your result, your skin, your latitude and the season, which is why I won't put a number here. That's a conversation with your physician.
Two things worth knowing
It's fat-soluble, so take it with a meal containing some fat. It's also stored rather than excreted, which is why it's one of the few vitamins where excessive doses can genuinely cause harm — too much raises blood calcium, which is a real problem.
More is not better. Very high-dose vitamin D is heavily marketed and there's no good evidence that pushing levels above the normal range helps anything. Aim for sufficient, not maximal.
This is general nutrition education, not medical advice, and it isn't intended to diagnose, treat, cure or prevent any condition. If you're pregnant or breastfeeding, taking medication, or managing a diagnosed condition, talk to your doctor or pharmacist before making changes.
Written by Mellissa Wallace, Registered Holistic Nutritionist, Okanagan BC.
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