Sunshine Vitamin

The Role of Vitamin D

Spring is around the corner and with this comes longer days and warm sunshine! Jill Weber, Nutrition & Health Field Specialist for Iowa State University Extension Service, said increased research is being conducted on the role of Vitamin D in our health.

Vitamin D is unique because it can be obtained in two different ways: from exposure to sunlight and from foods. Did you know a vitamin D precursor is produced in the skin upon exposure to the ultraviolet B (UV-B) rays of the sun? This precursor then circulates to the liver and on to the kidneys to be turned into the active form of vitamin D.

How does vitamin D fit into the picture of overall health? Calcium can be absorbed without vitamin D. However, vitamin D increases the efficiency and amount of calcium absorbed. If there is a vitamin D deficiency, calcium absorption from the intestine may decrease from approximately 30-50% to no more than 15%. The main role of vitamin D is to keep blood calcium levels in the normal range. It does this by increasing calcium absorption from the intestine and increasing calcium removal from the bones. If not enough calcium is consumed and absorbed, vitamin D will signal removal of calcium from the bones to maintain normal blood levels.

How much time do you need to spend in the sun to make vitamin D? It is generally thought that exposure of the hands, face, and arms three times a week for about 5-15 minutes is more than adequate. Many factors, including clothing and sunscreen, can block the UV-B radiation from the sun and prevent vitamin D production. This may not be a big issue for children and young adults because it is unlikely they will wear a sunscreen every time they are outdoors, nor will they likely cover all sun-exposed areas of the body. However, older adults may be more diligent in sunscreen application and/or have less sun exposure, especially during winter months when more time is spent indoors. Because older adults also have less of the vitamin D precursor in their skin, as well as kidney function that tends to decline with age, they are at greater risk for vitamin D deficiency.

What foods contain vitamin D? Most foods do not contain any vitamin D, nor are they fortified with it. Milk is one of the few foods to which vitamin D is added during processing. Other dairy products, such as cheese and yogurt, are poor sources of vitamin D because they are generally not made with fortified milk. Fatty fish and their oils (tuna, salmon, sardines, mackerel, and cod liver oils) are some of the few foods that naturally contain vitamin D. Small amounts of vitamin D are found in beef liver and egg yolks. Although nutrient needs should be met primarily through consuming foods, if you think you may not be getting enough vitamin D in your diet, talk with your health care provider about possibly taking a supplement to ensure adequate intake.

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More information about building a healthy diet is available from your local Franklin County Extension Office, 3 1^st Ave NW, 641-456-4811. You can also access nutrition information from our ISU Extension website 24 hours a day at: http://www.extension.iastate.edu/healthnutrition/