Most people think of vitamin D as just another nutrient on a blood test, something you might take in winter or if your doctor says you’re “low.” But vitamin D is far more than that. It’s a hormone, essential for life, influencing everything from bone strength to fertility, mood, and immune resilience.

And here’s the key: most lab reference ranges only show you where the average population sits — not what’s actually optimal for health. Being “within range” doesn’t necessarily mean your body has what it needs to thrive.

What Vitamin D Really Does

Vitamin D acts like a master regulator in the body. Once activated, it binds to receptors (called VDRs — vitamin D receptors) found in almost every tissue. That means it can influence:

Bone health & calcium absorption → Without it, calcium passes through the gut unused, leading to soft or brittle bones.
Immune regulation → Vitamin D “trains” your immune system — helping it fight infection while also calming inflammation.
Hormonal balance → Vitamin D interacts with the thyroid, reproductive organs, and even insulin production.
Brain & nervous system → Supports neurotransmitters that affect mood, learning, and memory.
Cell growth & repair → It helps regulate how cells grow, differentiate, and repair themselves.

This isn’t just about avoiding rickets. It’s about supporting the entire orchestra of the body to play in tune.

Optimal Levels vs. Reference Ranges

Most labs use a “normal” reference range of 30–100 nmol/L (12–40 ng/mL). But this is based on averages from the general population — and most of the general population is deficient.

From a naturopathic and functional medicine perspective, we often look for optimal levels closer to:

75–125 nmol/L (30–50 ng/mL) → for general wellbeing.
100–150 nmol/L (40–60 ng/mL) → for immune resilience, hormonal balance, and chronic disease prevention.

Anything below 50 nmol/L (20 ng/mL) is associated with increased risk of infections, bone issues, mood problems, and more.

Life Stages & Vitamin D

Vitamin D needs — and impacts — shift across different stages of life:

Infancy & Childhood → Critical for bone growth, brain development, and immune training. Low levels in children increase risk of rickets, frequent infections, and even autoimmune risk later in life.
Adolescence → Supports growth spurts, skin health, mood stability, and the hormonal changes of puberty. Deficiency here can set the stage for acne, irregular cycles, low mood, and fatigue.
Reproductive Years → Vitamin D influences ovulation, sperm health, and endometrial receptivity. Deficiency is linked with PCOS, endometriosis, infertility, and miscarriage risk.
Pregnancy & Breastfeeding → Demand skyrockets — vitamin D supports placental function, foetal bone and brain development, and reduces risk of preeclampsia and gestational diabetes. Babies born to vitamin D–deficient mothers often begin life already depleted.
Midlife → Helps regulate weight, mood, immune balance, thyroid health, and protects against metabolic issues.
Elderly → Supports bone strength, reduces fracture risk, protects cognition, and bolsters immune resilience. Older adults produce less vitamin D in their skin, making deficiency common.

Sunlight: Still the Best Source

Safe, regular sun exposure is the most effective way to build and maintain optimal vitamin D.
Aim for arms and legs exposed 3–4 times per week when the UV index is 3 or higher, without sunscreen, for around 10–20 minutes depending on your skin tone.
Remember: vitamin D isn’t stored efficiently, so regular top-ups are essential.

Food & Supplementation

Food sources: oily fish, egg yolks, liver, mushrooms (sun-exposed). Helpful, but not enough alone.
Supplements: While 1,000 IU per day is often recommended, it’s usually too low to raise levels meaningfully. For many, 2,000–5,000 IU daily is more realistic (always guided by testing and practitioner advice).
Toxicity is rare but possible — which is why testing matters.

Why This Matters

Deficiency isn’t just about weak bones. Research links low vitamin D with higher risk of:

Autoimmune disease (MS, type 1 diabetes, Hashimoto’s)
Mood disorders (seasonal affective disorder, depression)
Hormonal imbalance (PCOS, infertility)
Poor immune resilience (frequent infections, worse flu/COVID outcomes)

In other words: it’s a nutrient we can’t afford to ignore.

Sev’s Final Thoughts

Vitamin D is simple, but it’s not small. It’s one of the most powerful ways we connect with nature — through sunlight itself. Yet, it’s also one of the most overlooked nutrients in modern healthcare.

Checking your levels, aiming for optimal (not just “in range”), and working with food, sun, and smart supplementation can transform health at every life stage.

This is the kind of foundation naturopathy is built on: prevention, reconnection, and balance. Sometimes, the most powerful medicine really is the simplest.

Sev xx

Vitamin D: A Lifelong Hormone for Health