At Wasaga Beach's latitude — 44°N — the sun cannot make enough vitamin D in our skin from October through April. Most adults in Ontario are functionally deficient by mid-winter. The fix costs about ten dollars a year.
💡 Why this matters
Most Canadians have measurably low vitamin D from October through April because there isn't enough UVB sunlight at our latitude to support synthesis. A modest daily supplement (1,000–2,000 IU) is widely recommended through the dark months.
What vitamin D actually does
Vitamin D is more hormone than vitamin. It supports calcium absorption (bone health), modulates the immune system, plays a role in muscle function, and has been linked in observational studies to mood, cardiovascular outcomes, and cancer risk. The body makes it primarily through skin exposure to UVB sunlight — but only when the sun is high enough in the sky.
Why northern populations are low
Above ~37°N latitude, UVB intensity is too low for vitamin D synthesis from October through April. Wasaga Beach sits at 44°N. Even with regular outdoor time, the dominant route to adequate vitamin D in winter is supplementation. Estimates from population surveys put 30–40% of Canadian adults below the optimal threshold by late winter (Holick, 2007).
Test, do not guess
Before high-dose supplementation, ask your physician for a serum 25(OH)D test. Optimal range is generally 75–125 nmol/L. If you are above 75, modest maintenance is fine. If you are below 50, your physician may recommend higher loading doses for a few months.
Recommended doses
- 1,000–2,000 IU/day of vitamin D3 (cholecalciferol) is the typical adult maintenance dose recommended by Health Canada and Osteoporosis Canada
- Take with a fat-containing meal for best absorption
- D3 over D2: D3 raises serum levels more efficiently
- Pair with vitamin K2 if taking sustained higher doses
Caution at high doses
Vitamin D is fat-soluble — toxicity can develop with sustained intake above 10,000 IU/day. Stick within recommended ranges unless your physician guides higher dosing for diagnosed deficiency.
Vitamin D deficiency is now recognized as a pandemic.Source: Holick (2007), New England Journal of Medicine.
By the numbers
Daily supplementation through the dark months is one of the highest-return health investments at our latitude.
References
- Holick, M. F. (2007). Vitamin D deficiency. New England Journal of Medicine, 357(3), 266–281. View source →
- Osteoporosis Canada. (2024). Vitamin D Recommendations. View source →
- Health Canada. (2023). Vitamin D and Calcium: Updated Dietary Reference Intakes. View source →