Vitamin D and Sunlight
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
Sources: Wikipedia, Biochemistry 5th ed. Stryer et al.
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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Update: June 2012