Vitamin D3 is a form of vitamin D. Vitamin D, or calciferol, is a fat-soluble vitamin that plays a key role in maintaining bone health, supporting immune function and more, Heather Hodson, clinical nutritionist at the Center for the Prevention of Cardiovascular Disease at NYU Langone Health, tells TODAY.com.
There are two main forms of vitamin D: vitamin D3 and vitamin D2. They are similar but are obtained from different sources, per the NIH. These are both inactive when they are absorbed in the small intestine.
Vitamin D3, also known as cholecalciferol, is synthesized in the skin upon exposure to sunlight, says Hodson. "It can also be consumed through dietary sources like fish, and supplements," Hodson adds.
Vitamin D3 is fat-soluble. After its produced by the skin or ingested, vitamin D3 gets stored in our fat cells so our body can use it later.
Inside the body, vitamin D3 gets converted to calcidiol in the liver, which eventually gets converted to the active form of Vitamin D, calcitriol, in the kidneys, says Hodson. This is the form of vitamin D that the body can use.
Vitamin D2, also known as ergocalciferol or "pre-vitamin D," is typically human-made and found in some plant-based foods or added to fortified food products, per the NIH. Vitamin D2 is also converted into the active form of vitamin D in the liver and kidneys.
"Research demonstrates that compared to Vitamin D2, Vitamin D3 is more easily absorbed and may more effectively sustain desirable vitamin D levels,” Hodson adds.
Vitamin D3 offers various benefits for the body. It can help:
Vitamin D3 plays an important role in building and maintaining healthy bones, says Hodson. It does so by regulating calcium and phosphorus levels in the blood, and promoting the absorption of these minerals in the gut.
Calcium and phosphorus are essential minerals that act as building blocks for bones and teeth and play a role in muscle function, nerve transmission and energy production, research shows.
“(Vitamin D3) really supports our bone integrity, so it’s keeping your skeletal system nice and strong,” Zelle Morefield, a transplant dietitian at the Mayo Clinic tells TODAY.com.
Vitamin D3 is essential for bone remodeling, which repairs damage and adjusts bones over time as our bodies change, per the NIH. When we age, vitamin D3 can help prevent bone disorders, such as osteoporosis and bone loss.
Vitamin D3 also promotes muscle growth and strength which, in turn, support our bones and keep us balanced, per the NIH.
Vitamin D3 also supports the immune system to help the body fight off bacteria and viruses, and it has neuroprotective properties which support brain cell activity, per the Mayo Clinic.
"It has different anti-inflammatory and antioxidant properties as well, and it's just good for just overall cellular functions and helps a lot of smaller cellular processes," says Morefield.
The recommended dietary allowance (RDA) of vitamin D, or the daily intake sufficient to maintain bone health in healthy people, varies by age, per the NIH.
Vitamin D3 can be obtained in from foods, sunlight or supplements.
Few foods are naturally rich in vitamin D3, the experts note, which is why it's often added to food products. Fortified foods provide most of the vitamin D in American diets, according to the NIH.
Dietary sources of vitamin D3 include:
Vitamin D2 can be obtained from plant-based foods, including fortified plant milks, juices and mushrooms exposed to UV light, says Hodson.
"Vitamin D deficiency is not always characterized by noticeable symptoms," says Hodson. Some people have no signs of a vitamin D deficiency at all, which is why testing is important.
Potential symptoms of a vitamin D deficiency include:
Over time, vitamin D deficiency can lead to complications such as osteoporosis, which weakens the bones, and osteomalacia (a softening of the bones) and fractures, per the Cleveland Clinic.
“In older populations, deficiency may lead to increased fall risk,” says Hodson.
In severe pediatric cases, vitamin D deficiency can cause bowed legs or rickets, which leads to skeletal deformities, Hodson adds.
The only way to know if you have a vitamin D deficiency is to get tested. If you're at risk, semi-regular monitoring of vitamin D levels may help treat or prevent deficiencies in a timely manner, Hodson adds.
When taken as directed by a doctor, vitamin D3 is generally safe. However, getting too much vitamin D is not a good thing and can cause more problems, so it's important not to exceed your prescribed or recommended dosage, says Hodson.
"Vitamin D is a fat-soluble vitamin, (so) any excess that is consumed is stored in the body rather than excreted through urine," says Hodson. If you are taking too much in a supplement, it can built up in the body and reach toxic levels.
According to Hodson, vitamin D toxicity can lead to:
If you experience any side effects from taking D3, talk to your doctor. “When selecting a supplement, choose brands that are reputable and third-party tested,” says Hodson.
