Vitamin D is a fat-soluble vitamin that is obtained mainly from the sun. Very little vitamin D is obtained from foods due to its scarcity in the diet. There are two types of vitamin D: vitamin D2 and vitamin D3. Vitamin D2 is found is formed in plants and is not found in humans, while vitamin D3 is formed in the body when there is sunlight exposure.
Vitamin D2
Vitamin D2, or ergocalciferol, is created through plants. It is not naturally found in humans. You cannot obtain vitamin D2 in any significant quantity through plant products, however. Ergocalciferol can be obtained through a prescription from your doctor or can sometimes be found in over-the-counter supplements. A prescription for ergocalciferol can be written for 50,000 IU, and is used if you are found to be deficient. In over-the-counter supplements, it can be found in much smaller doses, such as 400 IU.
Vitamin D3 and Sunlight
Vitamin D3, or cholecalciferol, is considered a pre-hormone meaning that some of the cholecalciferol taken in will turn into hormones in the body. Cholecalciferol is formed in the body through exposure to sunlight and can also be provided in a supplement form. Exposure to sunlight for 20 to 30 minutes, allows your body to form 10,000 IU of vitamin D. Once the body forms the needed amount of vitamin D, it turns of the mechanisms to make it and therefore prevents you from getting an overdose from the sun.
Diet Sources and Supplements
Supplements may contain either vitamin D2 or D3, though D3 is more commonly found. According to the National Institutes of Health, both forms of the vitamin can effectively maintain serum vitamin D levels. Food can provide another source of vitamin D but few foods contain significant quantities. Foods that contain significant amounts of vitamin D include: cod liver oil, salmon, mackerel, tuna, vitamin D-fortified milk or yogurt, fortified orange juice, and ready-to-eat cereals. One cup of milk contains between 115 to 124 IU of vitamin D, while 1 tbsp. of cod liver oil contains 1,360 IU of vitamin D.
Recommended Intakes
Recently the Institute of Medicine has updated their recommendations for vitamin D intake in the population. Intake of 600 IU per day is recommended for people ages 1 to 70. Adults older than 70 are advised to have an intake of 800 IU per day. Due to the challenge of getting enough vitamin D through the diet, it may be necessary to supplement, especially if you live in an area of high latitude with limited sun exposure during certain times of the year, if you have dark skin, are obese, or elderly. These groups of people tend to be at higher risk of deficiency. Breast-fed infants all need a vitamin D supplement of 400 IU per day due to the low amount of vitamin D found in breast milk.
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