Vitamin D isn’t just a single nutrient—it’s actually a group of fat-soluble compounds essential for bone strength, immune support, muscle function, and calcium absorption. With so many supplement options on the shelf, it’s easy to wonder: Which form of vitamin D is best—D2 or D3?
Let’s break it down in a clear and practical way so you can choose what’s right for your health.
What Exactly Is Vitamin D?
Vitamin D, also known as calciferol, is unique because your body can make it naturally when your skin is exposed to sunlight. You can also get smaller amounts from foods like:
- Fatty fish (salmon, mackerel, sardines)
- Egg yolks
- Mushrooms exposed to sunlight
- Fortified foods like milk, cereals, and plant-based milks
Since food sources are limited, many people turn to supplements for support.
The Two Main Forms of Vitamin D
When it comes to supplements and fortified foods, you’ll see two primary forms:
Vitamin D2 (Ergocalciferol)
- Sourced from plants and fungi—often from UV-exposed mushrooms or yeast.
- Commonly used in fortified foods.
- Vegan-friendly.
Vitamin D3 (Cholecalciferol)
- Found naturally in animal sources like fish and cod liver oil.
- Most supplement D3 is derived from lanolin (sheep’s wool).
- Vegan versions from lichen are now available.
How Vitamin D Works in Your Body
Regardless of which form you take, your body processes vitamin D in two steps:
- Liver: Converts D2 or D3 into 25-hydroxyvitamin D [25(OH)D] — the storage form measured in blood tests.
- Kidneys: Convert 25(OH)D into 1,25-dihydroxyvitamin D (calcitriol) — the active hormone your body uses.
What Does a Vitamin D Test Measure?
Dr. Karen Tan checks your vitamin D3 levels through a blood test to determine how much supplementation you need to reach your optimal range.
D2 vs. D3: Which One Is Better?
| Feature | Vitamin D2 | Vitamin D3 |
| Source | Plants & fungi | Animal-based or lichen (vegan option) |
| Potency | Good | More potent and longer-lasting |
| Stability in
blood |
Moderate | Maintains levels more effectively |
| Best for | Vegans or
prescription needs |
General supplementation for most people |
Natural vs. Synthetic Vitamin D — Should You Be Concerned?
Most supplements are synthetic but bioidentical, meaning your body recognizes and uses them just like natural vitamin D from sunlight or food.
- D2 (synthetic): Produced by exposing yeast to UV light.
- D3 (synthetic): Usually derived from lanolin or lichen (vegan D3).
✔ Safe
✔ Effective
✔ Often more sustainable than animal harvesting
How Much Vitamin D Do You Need?
Here’s a simple guide based on ng/mL:
| Vitamin D Status | Level |
| Deficient | Less than 20 ng/mL |
| Insufficient | 20–29 ng/mL |
| Sufficient | 30–100 ng/mL |
| Optimal | 50–60 ng/mL |
| Toxic | Over 100 ng/mL |
👉 Ask Dr. Tan for a 25(OH)D blood test to check where you stand.
Choosing the Right Supplement
Here’s a quick guide to help you choose:
- Vegan or vegetarian? → Choose D2 or vegan D3 from lichen
- Want best absorption and potency? → Choose D3 (cholecalciferol)
- On prescription? → You may be given high-dose D2 or active D3 (calcitriol) for specific conditions
Consult Dr. Karen Tan before starting or adjusting supplements, especially if you have kidney, liver, or bone health concerns.
The Bottom Line
Vitamin D plays a powerful role in supporting your bones, immune health, and overall vitality. While both D2 and D3 can help, D3 is typically the most effective choice for maintaining healthy long-term levels.
Need help interpreting your vitamin D results or choosing the right supplement? Book a call with Dr. Karen Tan to guide you toward your optimal health.