Vitamin D: The Sunshine Hormone You Can’t Afford to Ignore

By: Dr. Mary Knudsen, ND, MSCP

Most people think of vitamin D as just another supplement — something you pop in winter and forget by summer. But here’s the truth: vitamin D isn’t just a vitamin. It’s a prohormone — meaning it acts more like a hormone than a nutrient. And for women of all ages, it’s one of the most essential (and most overlooked) keys to overall health and vitality.

Why Vitamin D Matters

Vitamin D supports nearly every system in the body. It helps:

• Build and preserve bone strength by improving calcium absorption
• Support mood and cognitive health through serotonin and dopamine regulation
• Bolster immune function to reduce inflammation and chronic disease risk
• Protect heart and muscle function by supporting vascular and metabolic health

In short, vitamin D helps keep your body’s inner architecture strong, your energy steady, and your immune system ready for whatever life throws at you.

The Deficiency Dilemma

Here’s the kicker: up to 40–60% of Canadian adults are vitamin D deficient, especially in winter. In northern latitudes, our skin makes virtually no vitamin D between October and April — even if you’re outdoors daily.

Other factors that lower vitamin D production include:

• Sunscreen use (yes, even SPF 15 blocks most synthesis)
• Darker skin pigmentation
• Aging skin (less efficient vitamin D conversion)
• Gut absorption issues
• Certain medications (like steroids or anti-seizure drugs)

Lab Testing: Determining What Your Body Really Needs

Testing your vitamin D levels is the only way to know if you’re getting enough — or perhaps too much. While deficiency is common, over-supplementation can lead to elevated calcium levels, kidney strain, and other metabolic issues.

A simple blood test — 25-hydroxyvitamin D (25(OH)D) — measures your stores.

• Deficient: <50 nmol/L
• Optimal: 75–125 nmol/L
• Toxic: >250 nmol/L (rare and supplement-related)

Testing takes the guesswork out of supplementation. It allows your healthcare provider to dose your vitamin D based on your actual needs, instead of supplementing blindly and hoping for the best.

In Alberta, vitamin D testing is not available to everyone on demand — it’s covered by Alberta Health only if you meet specific criteria, including:

• Metabolic bone disease (such as osteoporosis or osteomalacia)
• Abnormal blood calcium levels
• Malabsorption syndromes (like celiac disease, small intestinal surgery, or use of anticonvulsant medications)
• Chronic renal disease
• Chronic liver disease

If you don’t meet these criteria, your naturopathic doctor can requisition a vitamin D test for you privately, for a fee. This allows you to track your levels and tailor your supplement dosage with precision.

Testing at least once or twice a year — especially before and after supplementing — helps ensure you stay in the “Goldilocks zone”: not too low, not too high.

Food Sources: Small But Mighty

• Fatty fish (salmon, sardines, mackerel)
• Egg yolks
• Fortified plant milks or dairy
• Mushrooms exposed to UV light

Even so, diet contributes less than 10% of your total needs — hence the need for smart supplementation.

Vitamin D isn’t a quick fix — it’s a foundation

Get your vitamin D tested once or twice a year. In Alberta, check if you qualify under the public testing criteria — or ask your naturopathic doctor to requisition it privately. Testing allows us to dose your vitamin D appropriately and keep you thriving — not supplementing in the dark.