Vitamin D3 is important for brain health, strong bones, and anti-cancer properties. Learn which 5 foods to eat to get more Vitamin D3. Key Takeaways Vitamin D can boost your immunity and strengthen your bones. Vitamin D3 is the more effective form to maintain your body's vitamin D levels. Vitamin D comes from the sun, foods, and supplements. Here’s what vitamin D3 is and why your body needs it. What is vitamin D deficiency? Vitamin D deficiency means you don’t have enough vitamin D in your body. It primarily causes issues with your bones and muscles. Taking a vitamin D supplement or a multivitamin with vitamin D may help improve bone health. The recommended daily amount of vitamin D is 400 international units (IU) for children up to age 12 months, 600 IU for people ages 1 to 70 years, and 800 IU for people over 70 years. Several forms (vitamers) of vitamin D exist, with the two major forms being vitamin D 2 or ergocalciferol, and vitamin D 3 or cholecalciferol. [1] The common-use term vitamin D refers to both D 2 and D 3, which were chemically characterized, respectively, in 1931 and 1935. Cholecalciferol is vitamin D3. Vitamin D helps your body absorb calcium. Vitamin D is also essential for maintaining a healthy immune system. The function of the immune system is to prevent or limit infection. Cholecalciferol is used as a dietary supplement in people who do not get enough vitamin D in their diets to maintain adequate health. Medical experts explain how much vitamin D you should be taking per day, the differences between vitamin D2 and D3, and how much vitamin D is too much. Vitamin D3 helps your bones by improving calcium and phosphorus absorption. Low vitamin D3 levels can affect your mood and lead to feelings of sadness or anxiety. Vitamin D3 boosts your immune system by helping fight infections and controlling inflammation. Vitamin D3 helps your body absorb calcium, which is essential for healthy bones. Direct sunlight, foods like fatty fish and fortified dairy, and supplements are good sources of Vitamin D3.