Canada's geography creates a national vitamin D problem. For roughly half the year, the sun is too low in the sky for your skin to synthesize vitamin D at all. Here's what that means for your bones — and what to do about it.
Vitamin D isn't just a supplement trend. It plays a fundamental role in bone metabolism: your intestines need vitamin D to absorb calcium from food. Without adequate vitamin D, even a high-calcium diet won't fully protect your bones.
Beyond calcium absorption, vitamin D directly supports bone mineralization (the hardening process that makes bones dense and strong), reduces the risk of falls in older adults by improving muscle function, and helps regulate the hormones involved in bone turnover.
Your skin produces vitamin D when exposed to UVB radiation from the sun. The problem is that this only works when the sun is high enough in the sky — specifically, when the UV index is 3 or above.
In Canada, that window is surprisingly short:
| City | Months with adequate UVB |
|---|---|
| Vancouver | April – September (6 months) |
| Toronto | April – September (6 months) |
| Calgary | April – September (6 months) |
| Montreal | May – September (5 months) |
| Edmonton | May – August (4 months) |
| Winnipeg | May – August (4 months) |
For the other 4–8 months of the year, your body makes essentially zero vitamin D from sunlight regardless of how long you're outdoors. Add indoor lifestyles, sunscreen use, and darker skin tones (which require more sun exposure to produce the same amount of D), and the result is widespread deficiency.
Osteoporosis Canada recommends:
| Group | Recommended Daily Intake |
|---|---|
| Adults under 50 (low risk) | 400–1,000 IU |
| Adults over 50, or at higher risk | 800–2,000 IU |
| People with osteoporosis | 800–2,000 IU (under medical guidance) |
Health Canada's official recommendation is more conservative (600 IU for adults under 70, 800 IU for 70+), but Osteoporosis Canada and many Canadian physicians consider 1,000 IU/day a reasonable daily target for most adults, especially outside summer months.
A blood test measuring 25-hydroxyvitamin D (25(OH)D) is the most accurate way to know your status. Target levels for bone health are generally 75–150 nmol/L. Ask your doctor if testing makes sense for you — it's not routinely covered in all provinces but is often worth the out-of-pocket cost.
Unlike calcium, vitamin D is very difficult to get from food alone. The main dietary sources are:
Even with a diet rich in these foods, you're unlikely to reach 1,000 IU from food alone. For most Canadians, particularly in fall and winter, a supplement is the practical solution.
Vitamin D3 (cholecalciferol) is the form your skin makes naturally and is more effective at raising blood levels than D2 (ergocalciferol). Choose D3 unless you have a specific reason not to (some vegan D3 supplements are now made from lichen).
Vitamin D is fat-soluble, so it absorbs best when taken with a meal containing some fat. Softgels in an oil base tend to absorb well. Drops are convenient and allow easy dose adjustment.
You may have seen "D3+K2" supplements. There's a rationale here: vitamin K2 helps direct calcium into bones and teeth rather than soft tissues (like arteries). Some researchers believe supplementing high-dose D3 without K2 could theoretically increase calcium deposition in the wrong places, though this remains an area of active research.
For most people taking standard doses (1,000–2,000 IU D3/day), this isn't a major concern. But if you're supplementing at higher doses or have cardiovascular risk factors, a combined D3+K2 product is a reasonable choice.