Vitamin D. It’s often dubbed the “sunshine vitamin,” and it’s responsible for things like strengthening your bones, regulating your mood, and supporting your immune system. But vitamin D isn’t just one single nutrient—it’s actually a family of similar compounds that act as hormones in your body. The two key players of the group are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).

Both are important for maintaining overall health, but there are some key differences between vitamin D2 and D3 to know, especially if you’re considering getting more vitamin D via supplement. Here, we spoke with doctors and a registered dietitian to get the details about D2 vs. D3, including the best sources of each.

3 differences between vitamin D2 vs. D3

Both vitamin D2 and D3 are precursors to the active form of vitamin D in the body. That is to say, they’re both good for you and support healthy levels of vitamin D. But they differ in a few important ways:

1. D2 comes from plants, D3 comes from animals

Vitamin D2 (ergocalciferol) is actually a plant form of vitamin D, derived from mushrooms, yeasts, and other plants, says Lisa Andrews, RD, MEd, registered dietitian and owner of Sound Bites Nutrition. “Foods fortified with vitamin D, including dairy products, non-dairy products, and breakfast cereals, use vitamin D2,” she adds.

The National Institutes of Health (NIH) names the following as good vitamin D2 sources:

• Mushrooms exposed to UV light (½ cup): 366 IU
• Fortified soy, almond, or oat milk (1 cup): 100 to 144 IU
• Fortified, ready-to-eat cereal (1 serving): 80 IU

In contrast, “Vitamin D3, also known as cholecalciferol, is found in animal foods,” Andrews says. In particular, it’s found in milk with fat (1 percent, 2 percent, or whole milk), cheese, fatty fish (like herring, mackerel, salmon, and tuna), egg yolks, and liver, Andrews notes.

Here’s a look at how much vitamin D3 is in certain foods, per the NIH:

• Salmon (3 ounces): 570 IU
• Fortified 2 percent milk: 120 IU
• Sardines (2 sardines): 46 IU
• Egg (1 large): 44 IU
• Beef liver (3 ounces): 42 IU
• Light tuna (3 ounces): 40 IU

To get more vitamin D from food, your best best is to eat a variety of foods with D2 and D3.

2. Vitamin D3 is made from sunlight, but not D2

One of the main ways humans get vitamin D is through sunlight exposure. When we absorb the sun’s rays, our bodies naturally produce vitamin D in our skin, which can then transfer to our bloodstream, per Andrews. But it’s only D3 that our bodies make from sunlight, not D2.

“Ten to 15 minutes of sunlight per day provides roughly 1,000 IU of vitamin D3,” she says.

3. Vitamin D3 is more effective at improving blood vitamin D levels

Both vitamin D2 and vitamin D3 can raise your blood levels of vitamin D. But while your body can absorb both pretty well, vitamin D3 tends to be more effective at improving deficiency and maintaining your levels for longer than D2, per the NIH.

There are two reasons why: Vitamin D3 is more bioavailable (i.e., better used by your body), and its supplement form more closely resembles the vitamin D3 your body makes, says Jennie Stanford, MD, FAAFP, an obesity medicine physician and medical contributor for Drugwatch.

That said, because vitamin D3 comes from animals, Dr. Stanford says people following a vegan or vegetarian diet may prefer to use vitamin D2 supplements. Though some plant-based vitamin D3 formulations are becoming more readily available, she adds.

If you want to start taking a vitamin D3 supplement, talk to your doctor first to confirm it’s right for you and to determine the best dosage. Then look for a supplement that has been third-party tested for quality by either USP or NSF (usually products carry a seal on their label), such as Nature Made Vitamin D3 or Thorne Vitamin D-5,000.

When choosing a vitamin D3 supplement, look for one with the right amount of vitamin D for your needs (talk to your doctor  that has been third-party tested for

How much vitamin D2 and D3 should I get per day?

Vitamin D requirements will vary by age, according to Andrews and the NIH. Recommendations are provided in both IU (international units) and micrograms (with 40 IU equal to 1 microgram).

“Those aged 19 to 70, including people who are pregnant or lactating, need 600 IU (15 micrograms) of vitamin D daily, while those over 70 need 800 IU (20 micrograms) daily,” says Andrews. Recommendations don’t differentiate between vitamin D2 and vitamin D3, as both can raise blood levels of vitamin D.

What about when you have a vitamin D deficiency? After all, between 92 and 97 percent of people get less than 400 IU of vitamin D per day, according to a National Health and Nutrition Examination survey by the Centers for Disease Control and Prevention.

“The amount of vitamin D a person with a deficiency needs to reverse it will vary depending on the level of vitamin D in their blood,” Andrews says. If you suspect you have a vitamin D deficiency, it’s important to get blood work done to tailor your vitamin D dose to your specific needs.

For example, Andrews explains that people with vitamin D levels of 12 ng/mL (30 nmol/L) may need a prescription dose of 50,000 IU of vitamin D once per week, or 4,000 IU daily for six to eight weeks. Once your vitamin D level is stable, most people need to take 1,000 to 2,000 IU daily to maintain their supply. But of course, talk to your healthcare provider before making any dose adjustments.

Is it possible to get too much?

Yep. Vitamin D is fat-soluble, meaning it gets stored and built up in your body’s fat tissue. Getting too much vitamin D is dangerous because it can cause high levels of calcium in the blood—leading to nausea, vomiting, muscle weakness, loss of appetite, dehydration, kidney stones, and more, per the NIH. If you take more than 4,000 IU daily on a regular basis, ask your doctor if this is safe and necessary for you.

Who’s at risk for vitamin D deficiency?

A few things can put you at higher risk for a vitamin D deficiency. The first is certain health conditions, like celiac disease, Crohn’s disease, cystic fibrosis, kidney and liver disease, per Andrews and the NIH. Taking certain medications—like laxatives, cholesterol-lowering drugs (colestipol, cholestyramine, or statins), steroids, or seizure medication—can also increase your risk.

Beyond that, things like living in a geographical location with little sunlight or being homebound (i.e., people who are sick, immobile, older, or infants) can increase your vitamin D deficiency risk.

If any of these apply to you, it’s worth talking to your doctor about ways to increase your vitamin D levels, and what kind of supplement to take, to many sure you’re getting enough.