There are two main types of vitamin D: vitamin D2 and vitamin D3. Both can raise your blood levels and support bone health, but they aren’t identical. Vitamin D3 is roughly twice as effective as D2 at raising the blood marker doctors use to measure your vitamin D status. Understanding the difference helps you choose the right supplement and get more from your diet.
Vitamin D2 vs. D3: The Key Difference
Vitamin D2 (ergocalciferol) comes from plant sources, while vitamin D3 (cholecalciferol) comes from animal sources and sunlight. The two molecules are nearly identical, differing only by a small structural change in their side chains. That minor chemical difference, though, has a meaningful effect on how well your body can use them.
Vitamin D3 raises serum 25(OH)D levels, the standard blood test for vitamin D status, about two-fold higher than the same dose of D2. When researchers gave both forms simultaneously, D2 actually reduced the ability of D3 to raise blood levels. This is why most doctors and dietitians now recommend D3 when you have a choice.
D2 still works. It’s the form used in many prescription vitamin D supplements and in most fortified plant-based foods. If you’re vegan and D2 is your only option, it will raise your levels, just less efficiently per unit.
Where Each Type Comes From
Vitamin D2 is naturally found in mushrooms and yeast, which produce it when exposed to ultraviolet light. It’s also the form typically added to fortified foods like plant-based milks, orange juice, and cereals.
Vitamin D3 is the form your skin makes when exposed to sunlight. In food, it shows up in fatty fish like salmon and sardines, egg yolks, and beef liver. Supplements sourced from lanolin (sheep’s wool oil) provide D3, and lichen-derived D3 supplements are available for people who avoid animal products entirely.
How Your Body Activates Vitamin D
Neither D2 nor D3 is active when you first consume it or make it in your skin. Your body has to convert it through two steps. First, the liver adds a chemical group to create 25-hydroxyvitamin D, the form measured in blood tests. Then the kidneys perform a second conversion, producing the fully active hormone that regulates calcium absorption, bone remodeling, and immune function.
This two-step activation process is why kidney disease can lead to vitamin D deficiency even when intake is adequate, and why blood levels of the intermediate form (25-hydroxyvitamin D) are the most useful marker of your overall vitamin D status.
How Sunlight Factors In
Your skin produces D3 when UVB rays hit a cholesterol-related compound in the upper skin layers. Several factors determine how much you actually make:
- Latitude and season. At latitudes around 40 degrees north (think Boston) or south, there’s not enough UVB radiation from November through early March to produce meaningful vitamin D. Ten degrees farther from the equator, that “vitamin D winter” stretches from October to April.
- Skin tone. Melanin competes with the vitamin D precursor for UV absorption, acting as a natural sunscreen. People with darker skin may need up to ten times longer in the sun to produce the same amount of D3 as someone with fair skin.
- Age. Older adults have lower concentrations of the skin precursor needed to make vitamin D, reducing their synthesis capacity compared to younger people.
If you live in a northern climate, have darker skin, or are over 65, you’re more likely to need dietary or supplemental vitamin D to stay in a healthy range.
Healthy Blood Levels and What They Mean
The standard blood test measures total 25-hydroxyvitamin D in nanograms per milliliter (ng/mL). Here’s how to read your results:
- Deficient: below 20 ng/mL
- Insufficient: 21 to 29 ng/mL
- Sufficient: 30 ng/mL and above
- Toxic: above 150 ng/mL
The normal reference range runs from 25 to 80 ng/mL. Most experts aim for at least 30 ng/mL, and levels in the 40 to 60 range are often considered optimal, though recommendations vary by organization.
How Much You Need Daily
The National Academies of Sciences, Engineering, and Medicine sets the recommended daily intake at 600 IU (15 mcg) for most people ages 1 through 70, including during pregnancy and breastfeeding. Adults over 70 need 800 IU (20 mcg). Infants under one year have an adequate intake of 400 IU (10 mcg).
These are baseline recommendations for people with some sun exposure and a varied diet. Many clinicians recommend higher doses for people who are already deficient, though toxicity generally only occurs at sustained daily intakes above 10,000 IU. At very high levels, excess vitamin D causes the body to absorb too much calcium, a condition called hypercalcemia that can affect the kidneys and heart.
Getting the Most From Supplements
Vitamin D is fat-soluble, so it absorbs best when taken with a meal containing some fat. Research presented at the European Congress of Endocrinology found that vitamin D3 dissolved in milk or water was more effectively absorbed than other delivery methods in women with deficiency. Oil-based softgel capsules and liquid drops are popular for this reason, since the fat is built into the supplement itself.
If you’re choosing a supplement, D3 is the stronger option for most people. Look for it on the label as “cholecalciferol.” D2 (ergocalciferol) is perfectly fine if it’s what’s available or if you prefer a plant-sourced option, but you may need a somewhat higher dose to reach the same blood level. Either way, a simple blood test can tell you whether your current approach is working.