Vitamin D: More Than a Vitamin

Why Vitamin D is Actually a Hormone

Despite its name, vitamin D isn't technically a vitamin—it's a prohormone. Your body can synthesize it from sunlight (UVB rays) hitting your skin, converting cholesterol into active vitamin D.

Unlike true vitamins, which must come from diet, vitamin D acts more like a hormone: it binds to receptors in nearly every cell in your body, influencing gene expression and regulating hundreds of physiological processes.

What Vitamin D Does

🦴 Bone Health

Regulates calcium absorption. Deficiency leads to rickets (children) and osteomalacia (adults).

🛡️ Immune Function

Modulates innate and adaptive immunity. Deficiency increases infection risk and autoimmune conditions.

😊 Mood & Mental Health

Low vitamin D is linked to depression and seasonal affective disorder (SAD).

💪 Muscle Function

Supports muscle strength and reduces fall risk in older adults.

❤️ Cardiovascular Health

Low levels associated with hypertension and increased heart disease risk.

🧬 Cancer Prevention

Emerging research suggests vitamin D may reduce risk of certain cancers.

Understanding Your Vitamin D Levels

Lab test: 25-hydroxyvitamin D [25(OH)D] is the standard marker. It reflects your total vitamin D status.

25(OH)D Level	Status	Action
< 20 ng/mL	Deficient	High-dose supplementation needed
20-30 ng/mL	Insufficient	Supplementation recommended
30-50 ng/mL	Sufficient	Maintain current intake
50-80 ng/mL	Optimal	Ideal for most health benefits
> 100 ng/mL	Excess	Reduce supplementation

Optimal vs. Sufficient

While >30 ng/mL is considered "sufficient" to prevent bone disease, many functional medicine practitioners recommend targeting 40-60 ng/mL for optimal immune function, mood, and longevity benefits.

Why Deficiency is So Common

•Limited sun exposure: Indoor lifestyles, sunscreen use, living in northern latitudes
•Darker skin: Melanin reduces vitamin D synthesis, increasing deficiency risk
•Age: Older adults produce less vitamin D from sun exposure
•Obesity: Vitamin D is fat-soluble and gets sequestered in adipose tissue
•Limited dietary sources: Few foods naturally contain vitamin D (fatty fish, egg yolks, fortified milk)

Alarming statistic: An estimated 42% of US adults are vitamin D deficient, with higher rates among certain populations.

How to Optimize Your Vitamin D

☀️ Sunlight (The Natural Way)

✓10-30 minutes of midday sun exposure (without sunscreen) on arms/legs, 2-3x/week
✓Darker skin requires more exposure time
→Caveat: Balance with skin cancer risk. Avoid sunburn. Not feasible in winter for northern latitudes.

💊 Supplementation (Most Reliable)

Recommended doses:

•Deficient (<20 ng/mL): 5,000-10,000 IU daily for 8-12 weeks, then retest
•Insufficient (20-30 ng/mL): 2,000-5,000 IU daily
•Maintenance: 1,000-2,000 IU daily (once levels are optimal)

Form: Vitamin D3 (cholecalciferol) is more effective than D2 (ergocalciferol).

Take with fat: Vitamin D is fat-soluble. Take with a meal containing healthy fats for best absorption.

🥗 Food Sources (Supplementary)

•Fatty fish (salmon, mackerel, sardines): 400-1,000 IU per serving
•Egg yolks: ~40 IU per egg
•Fortified milk/orange juice: 100 IU per serving
•Mushrooms exposed to UV light: Variable amounts

Reality check: Diet alone rarely provides sufficient vitamin D for those with deficiency.

Cofactors: Don't Forget These

Vitamin D works synergistically with other nutrients. For optimal absorption and function, ensure adequate:

•Magnesium: Required to convert vitamin D to its active form. Many people are also magnesium-deficient.
•Vitamin K2: Directs calcium to bones (not arteries). Take with vitamin D for bone health.
•Calcium: Vitamin D enhances calcium absorption. Ensure adequate intake from diet or supplements.

When to Retest

•After starting supplementation: Retest in 8-12 weeks to assess response
•Once optimal: Retest annually or if symptoms of deficiency return
•Seasonal testing: Consider testing in late winter (lowest levels) and late summer (highest levels)