What's the Difference Between Vitamin D2 and D3?

Vitamin D (nicknamed the "sunshine vitamin") gets a lot of attention for its potential health benefits, ranging from boosted immune health to improved mood. But you may not know that the vitamin comes in two forms: D2 and D3.

Both vitamin D2 and D3 provide the same benefits to the body, says Michael F. Holick, PhD, MD , professor of pharmacology, physiology, and biophysics at Boston University Chobanian & Avedisian School of Medicine in Massachusetts.

However, there are a few key differences between the two forms.

What's the Difference Between Vitamin D2 and D3?

Once ingested, vitamin D2 (ergocalciferol) and D3 (cholecalciferol) are absorbed in the small intestine. From there, they enter the bloodstream and move to the liver where they're converted by an enzyme into new forms. Later, they enter the kidneys to be converted by another enzyme into their biologically active forms. Once all of this takes place, Dr. Holick says, the vitamin D molecules travel through the body to perform their various functions.

"The key difference between the two forms of vitamin D is in their structure," Holick says. The two compounds have different side chains (chemical groups attached to a molecule). This structure difference makes vitamin D3 easier to convert into its usable form after being consumed.

"The enzymes that convert vitamin D in the body prefer vitamin D3 to vitamin D2," says Qianzhi Jiang, PhD, RDN , founder of The Nutrition Changer, a nutrition services company in Natick, Massachusetts, and an adjunct professor at Framingham State University.

So, while vitamin D2 and D3 perform the same functions, your body metabolizes vitamin D3 more efficiently than D2.

Another key difference between the two forms of vitamin D is their source. "Vitamin D2 is usually produced by plants when exposed to sunlight," Dr. Jiang says. Meanwhile, vitamin D3 is found in animal products like fatty fish. It's also the type our bodies make when ultraviolet (UV) rays from sunlight touch our skin.

Health Benefits of Vitamin D: Differences in D2 vs. D3

Vitamin D helps our bodies absorb calcium and plays a key role in bone growth and maintenance. It also reduces inflammation and helps many body processes, including cell growth, immune function, and glucose metabolism.

While vitamin D2 and D3 come from different sources, they both offer these benefits, Holick says.

The Best Sources of Vitamin D2 vs. D3

Most healthy children and adults ages 1 to 70 years should get 15 micrograms (mcg) of vitamin D daily, while those over age 70 should get 20 mcg daily, per the National Institutes of Health (NIH).

You might score your recommended daily intake by getting vitamin D3 from sunlight. Research suggests that exposing your skin (without sunscreen ) to direct sunlight for 5 to 30 minutes will supply enough vitamin D for the day.

But too much sun exposure can increase your skin cancer risk.

What's more, different skin colors produce vitamin D3 at different rates - more pigmentation in the skin (darker skin colors) is associated with less vitamin D synthesis.

So it can be a good idea to also consider diet when it comes to meeting your vitamin D needs. Vitamin D2 is found in plants. Some mushrooms contain small amounts (0.1 mcg per half-cup), but mushrooms that have been treated with UV light provide much larger amounts (9.6 mcg per half-cup).

Some foods, like dairy and cereal products, are fortified with vitamin D2. You can also find vitamin D2 supplements. For most people, the primary source of vitamin D3 is its production in our skin after exposure to sunlight. However, you can also find vitamin D3 in animal products. Excellent sources of vitamin D3 noted by the NIH include:

• Cod liver oil: 34 mcg per 1 tablespoon (Tbsp)
• Trout: 16.2 mcg per 3 ounces (oz)
• Salmon : 14.2 mcg per 3 oz
• Sardines: 1.2 mcg per 2 sardines
• Eggs : 1.1 mcg per egg
• Beef liver: 1 mcg per 3 oz

Just like vitamin D2, vitamin D3 can be used to fortify dairy products and cereal, and it's found in many supplements.

When It Comes to Vitamin D Supplements, Should I Take D2 or D3?

Research shows that 49 to 77 percent of the U.S. population doesn't get enough vitamin D.

It can be difficult to tell if you have a vitamin D deficiency, but potential signs include mood changes, muscle weakness or cramps, fatigue, bone and joint pain, and bone loss.

If you're concerned that you're not getting enough vitamin D from sun exposure and diet, your doctor can test the vitamin D levels in your blood.

They may recommend using a vitamin D supplement if your levels are low.

But should you take vitamin D2 or D3?

" Vitamin D3 supplements are preferred as they are generally considered more effective than vitamin D2 supplements and similar to what our skin produces," Jiang says. In fact, research shows that vitamin D3 supplements lead to a greater boost in blood concentration of vitamin D than vitamin D2 supplements.

Vitamin D2 supplements are made from yeast and may be a better choice if you prefer to avoid supplements made from animal products. Most vitamin D3 supplements are produced with lanolin, a substance extracted from sheep wool, Jiang explains. However, she notes that a vegan form of vitamin D3 (made from fungus and algae) is also available.

Cod liver oil can also be a good vitamin D supplement because it offers 170 percent of the daily value (DV) per tablespoon, all from vitamin D3.

"However, high doses of cod liver oil may contain too much vitamin A , which can be toxic to humans," Jiang says. Consult your doctor before taking cod liver oil as a supplement.

Regardless of which type of vitamin D you choose, visit your doctor for a follow-up blood test to check that the supplement is working. If your vitamin D levels have increased, your supplement - whether it's D2 or D3 - is doing its job.

The Takeaway

While vitamin D2 and D3 perform the same functions in the body, they differ in structure, how they're metabolized by the body, and their sources. Vitamin D2 is found in plant foods, whereas D3 is produced by our skin when exposed to sunlight and is easier for our bodies to convert into a usable form. If you don't get enough vitamin D from sunlight and food, a vitamin D3 supplement may help boost vitamin D levels in your blood more efficiently than a vitamin D2 supplement, but both can help overall levels.

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