Vitamin D: What Your Lab Results Actually Mean

Vitamin D is one of the most commonly tested lab markers, yet it’s also one of the most misunderstood.

Let’s break down what your results actually mean.

The Basics

Vitamin D isn’t really a vitamin—it’s a hormone your body produces when exposed to sunlight. Most lab tests measure 25-hydroxyvitamin D (25(OH)D), the storage form in your blood.

Reference Ranges

Most labs use these general categories:

Level	Status
< 20 ng/mL	Deficient
20-29 ng/mL	Insufficient
30-100 ng/mL	Sufficient
> 100 ng/mL	Potentially harmful

However, there’s debate about optimal levels. Some researchers suggest 40-60 ng/mL for optimal health, while others are comfortable with anything above 30 ng/mL.

Factors That Affect Your Levels

• Sun exposure: The primary source for most people
• Skin tone: Darker skin requires more sun exposure
• Latitude: Living further from the equator reduces synthesis
• Age: Older adults produce less vitamin D
• Body weight: Vitamin D is fat-soluble and can be “sequestered” in fat tissue

Testing Frequency

If you’re deficient, most practitioners recommend testing every 3 months until levels stabilize, then annually.

Tracking Over Time

Single snapshots are helpful, but tracking vitamin D over time gives you better insight into:

• Seasonal variations
• Supplement effectiveness
• Your personal baseline

This is where having all your results in one place becomes valuable. You can see patterns that a single test might miss.