According to scientists, we should consume about 400 to 800 IU of vitamin D daily because it plays an important role in strengthening the immune system. Many of us are deficient in vitamin D, but because its symptoms are mild, we rarely notice it. But not everyone on Earth is deficient in vitamin D, why? For example, in areas close to the equator, because there is constant sunlight, they are usually not deficient in vitamin D.Vitamin D is difficult to obtain from ordinary food sources, and providing the body with the required amount is not possible only through the consumption of vitamin D sources.