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Name: Michelle
Status: Student
Grade:  9-12
Location: CA
Country: United States
Date: September 2006

How does vitamin D aid the absorption of calcium? What is the role of sunlight in the process?

Scientists today think the major role of Vitamin D in the body is to regulate calcium levels. There are several major forms of vitamin D, and the vitamin D that is made in the body, Vitamin D3, is a product of the reaction of a molecule of cholesterol with UVB radiation found in sunlight. This is then converted by the body to calcitriol in the liver and kidneys. Calcitriol binds to and activates proteins known as transcription factors which regulate the production of proteins that are involved in calcium transport and absorption.

There is a childhood diseases known as rickets that is a result of Vitamin D deficiency. According to Lubert Stryer's textbook Biochemistry, the disease was so prevalent in the sunlight-deprived country of Britain that at one point it was known as "the children's disease of England" (taking cod-liver oil, high in Vitamin D, became a common but insipid remedy, today many foods are fortified in Vitamin D). The adult version is still common among Bedouin Arab women who are clothed so that only their eyes are exposed to sunlight.

Sources: Wikipedia, Biochemistry 5th ed. Stryer et al.

Ethan Greenblatt
Stanford Department of Chemistry

Vitamin D stimulates the synthesis of various proteins that are resposible for absorbing Calcium from the intestine into cells lining the intestine. Sunlight stimulates the synthesis of Vitamin D in skin cells.

Ron Baker, Ph.D.

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