What Is Vitamin D?
Vitamin D is a fat-soluble vitamin — technically a hormone precursor — that your body produces in response to sunlight. The blood test measures 25-hydroxyvitamin D (25-OH vitamin D), the storage form.
It's one of the most common deficiencies in Canada, affecting 40–50% of adults.
Why Canadians Are Particularly at Risk
Canada's latitude means meaningful UVB exposure is only available for roughly five to six months of the year. From October to April, even spending time outdoors doesn't produce meaningful vitamin D.
What Low Vitamin D Affects
- Immune dysfunction — increased susceptibility to infections and autoimmune conditions
- Bone health — essential for calcium absorption
- Mood and depression
- Cardiovascular risk
- Fatigue and muscle weakness
- Cognitive function
Vitamin D Reference Ranges
Below 30 nmol/L: Deficient. 30–49: Insufficient. 50–125: Adequate. 75–125: Optimal (Stem Health target). Above 250: Potentially toxic.
How to Improve Vitamin D Status
- D3 supplementation — 2,000–5,000 IU/day typical therapeutic doses
- Sunlight — 10–30 minutes midday in summer; not reliable in Canadian winter
- Food sources — fatty fish, egg yolks, fortified milk; rarely sufficient alone
- Vitamin K2 co-supplementation — recommended alongside high-dose D3
Is Vitamin D Tested in a Standard Physical?
Sometimes. Stem Health includes vitamin D in every Core and Horizon Assessment.
