Vitamin D2 is the plant form of vitamin D; vitamin manufacturers use it in supplements and multivitamins, according to Mayo Clinic. People take vitamin D supplements to treat osteoporosis and prevent fractures, calcium deficiency, heart disease and falls.
Vitamin D exists in several forms, but humans use D2 and D3. Vitamin D3 is the form produced by human skin with exposure to ultraviolet light from the sun. Food manufacturers fortify their foods with either of the two forms, reports Mayo Clinic. Vitamin D is essential to maintaining the levels of calcium and phosphorous in the blood. These minerals are necessary for building and maintaining bone density. Exclusively breastfed babies, the elderly, the obese and people with limited exposure to the sun have the greatest risk of a vitamin D deficiency.
As of 2015, most multivitamins include 50 to 100 international units of vitamin D; however, the guidelines for vitamin D recommend 600 units daily for anyone between 1 and 70, explains Mayo Clinic. After age 70, the amount increases to 800 units. Doctors prescribe larger amounts for specific conditions.
Healthy individuals who spend 15 minutes in the sun three times per week produce enough vitamin D to meet their body's requirement without the use of supplements, states MedlinePlus. However, sunlight filtered through clouds or windows does not produce sufficient amounts of vitamin D.