You also need vitamin D for other important body functions. Vitamin D deficiency has now been linked to breast cancer, colon cancer, prostate cancer, heart disease, depression, weight gain, and other maladies. To get enough vitamin D, you only need thirty minutes of sun exposure to the face, legs, or back -- without sunscreen -- at least twice a week. Apart from the vitamin D synthesized in our skin when exposed to UVB light from sun, vitamin D can also come from nutrition: in salmon, mackerel, mushrooms, cod liver oil, canned tuna or sardines, milk or yogurt, egg yolks and fortified foods or supplements.
The vitamin D levels needed for the body vary depending the age. For infants from 0 to 12 months: 400 IU per day; for children aged 1 to 3 years: 600 IU per day, maximum 2500 IU per day; for children aged 4 to 8 years: 600 IU per day, maximum 3000 IU per day; from age 9 to 70: 600 IU per day, maximum 4000 IU per day; and for people aged over 71: 800 IU per day, maximum 4000 IU per day.
The benefits of vitamin D are numerous. Apart from helping calcium build strong bones, vitamin D helps regulate the immune system and the neuromuscular system. It regulates over 200 genes, in cells all over the body - including the brain, heart, kidney, bone, intestine, skin, gonads, prostate, breast, parathyroid gland, and immune system. So if you are still asking the question why do I need vitamin D, be aware that vitamin D is also essential for the human body to function properly.