Vitamin D: Not Just The Sunshine Vitamin

As summer approaches, longer days, warmer weather and more sunlight begin to grace our days. Here in Canada, where sunlight can be limited for much of the year, vitamin D plays an important (and often overlooked) role in our health.

While many view vitamin D as just another vitamin, it is more accurate to think of it as a steroid hormone that plays a role in everything from bone health to immune function.

Vitamin D is both a fat-soluble vitamin and a “hormone”, meaning it can be obtained through diet, but it is also produced by the body in response to sunlight. Once activated, it acts throughout the body, helping regulate nutrient absorption, metabolic processes, and overall balance.

Where Do We Get Vitamin D?

Sunlight (Primary Source)

• Your body produces vitamin D when your skin is exposed to ultraviolet B (UVB) radiation from the sun. This is the most efficient and natural way to maintain adequate levels.

Food Sources

• Vitamin D is found in a few foods, including fatty fish, liver, eggs, and fortified foods (milk, plant-based milks, cereals)

• For most people, especially in northern climates, food alone is not enough to meet optimal vitamin D needs.

UVA vs. UVB vs. UVC: Why Sunlight Matters

Not all sunlight is created equal when it comes to vitamin D production.

UVA (320-400 nm)

• Penetrates deeper into the skin and contributes to skin aging and damage, but does not significantly stimulate vitamin D production.

UVB (290–320 nm)

• This is the key player in vitamin D synthesis. UVB rays penetrate the skin and trigger the conversion of a cholesterol precursor into vitamin D.

  • UVB rays do not penetrate glass, so sitting by a sunny window doesn’t help

  • Production is reduced in:

    • Older adults

    • Individuals with darker skin tones

• Typically, 5–30 minutes of midday sun exposure (10 AM–4 PM) on uncovered skin can support adequate production

UVC (200-290 nm)

• Completely absorbed by the ozone layer and does not reach the earth’s surface.

Understanding The UV Index

The UV Index is a helpful tool that measures the strength of ultraviolet radiation at a given time and location. It ranges from 0 to 11+, with higher numbers indicating greater intensity and risk of skin damage.

Factors influencing the UV Index include:

• Time of day

• Season

• Latitude and altitude

• Cloud cover

• Ozone levels

At higher UV levels, sunburn can occur in under 10 minutes, so timing and duration of sun exposure matter.

How Vitamin D Is Made & Activated

Vitamin D synthesis is a multi-step process:

(1) Skin

• UVB rays convert a cholesterol-derived compound into vitamin D₃ (cholecalciferol)

(2) Liver

• Vitamin D₃ (from sunlight or dietary sources) is converted into 25-hydroxyvitamin D, the storage form measured in bloodwork

(3) Kidneys

• It is then converted into its active form, 1,25-dihydroxyvitamin D (calcitriol)

What Does Vitamin D Do?

Vitamin D plays a wide range of roles in the body:

• Bone Health: enhances calcium and phosphorus absorption for strong bones and teeth

• Immune Function: helps regulate immune responses and may reduce susceptibility to infections

• Inflammation Regulation: supports balanced inflammatory pathways

• Mood & Mental Health: low levels have been associated with mood changes, including seasonal depression

• Glucose Metabolism: plays a role in insulin sensitivity and blood sugar regulation

• Cardiovascular Health: may support heart and vascular function

Vitamin D Deficiency

Vitamin D deficiency is extremely common, particularly amongst Canadians.

• More than 50% of the global population is estimated to be at risk

• In Canada, deficiency is particularly prevalent due to:

  • Long winters

  • Limited sun exposure

  • Higher latitudes

Common Signs May Include:

• Fatigue

• Frequent illness

• Muscle aches or weakness

• Low mood

A simple blood test measuring 25(OH)D levels can determine your vitamin D status.

Vitamin D Toxicity

While deficiency is common, it is possible to take too much vitamin D, typically through high-dose supplementation.

Potential Effects of Toxicity:

• Elevated calcium levels (hypercalcemia)

• Nausea, vomiting

• Kidney strain

• Confusion or weakness

It is important to note that toxicity is NOT caused by sun exposure, as the body regulates how much vitamin D is produced through the skin.

Let’s Find The Right Balance

Vitamin D plays a foundational role in your health, but your needs are unique. Testing your levels can provide clarity and help guide safe and effective supplementation.

If you’re unsure where your levels stand or want support optimizing your vitamin D status, we can create a plan tailored specifically to you.

Book an appointment to review your levels, discuss your symptoms, and build a strategy that supports your health year-round.

Learn more or book an appointment at:

kathrynkingnd.com