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Penn State
Poultry T \
Pointers r
THE IMPORTANCE
OF VITAMIN D
Carol V. Gay
Professor of
Molecular CeD
Biology And
Poultry Science
The history of vitamin D goes
tack a long way. Rickets, a result
if vitamin D deficiency, was
lescribed in 1645.
However, it wasn’t until the
920 s that cures for rickets, a dose
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Idrei
of cod liver oil or sunlight, pro
vided clues for the biochemical
sleuthing that led to the purifica
tion of vitamin D.
The roles of vitamin D in tissues
are now fairly well known. These
are similar in both mammals and
non-laying birds. Vitamin D, once
ingested or converted in the skin
from a precursor, is modified in the
liver by one simple reaction to a
new form, now called 25-hydroxy
vitamin D. After this, the kidney
adds on another hydroxyl group to
form 1,25-(dihydroxy) vitamin D.
This latter compound is the
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active focm of the vitamin and it
has seven! precise roles. In the
intestine. 1,25-vitamin D stimu
lates the production of a protein in
intestinal cells. This special pro
tein binds calcium in digested food
and moves the calcium across the
intestinal wall into the bloods
tream. Without vitamin D, very
little calcium can enter the body—
thus rickets and other problems
with mineralization occur.
Vitamin D acts on bone cells to
enhance both bone resorption and'
formation. The resulting bone
remodeling allows for mainte
nance of strong bones while pro
viding calcium for body functions.
It’s much like using and main
taining a bank account In the kid
ney, 1.25-vilamin D is linked with
retention of calcium. Overall, vita
min D assists the body in acquiring
calcium (intestinal effect), storing
calcium.(bone effect), and retain
ing calcium (kidney effect).
Above and beyond these effects,
many types of cells are being
found to bind vitamin D, including
cells in bone marrow. The possi
bility that 1.25-viiamin D may be
lock in profits!
Moll To:
JOHN McFADDEN
1966 Baker Road
Man Mm. PA 17545
Ml Box (NO) 272*4774 ■
Ext 0019# I
useful in treating certain leukemias
has stirred some excitement
One might wonder why the
body goes to the trouble of using
two steps at two different sites (liv
er and kidney) to make the final
form of the vitamin. 1,25-vitamin
D. Apparently, the reason is that
2S-hydroxy vitamin D is a storage
form of the vitamin. Small
amounts of this are converted to
1,25-vitamin D in a way that is
very tightly controlled. This allow
s the body to retain a supply of this
fat-soluble vitamin for many days
and avoids the need for daily
ingestion.
Laying birds have an especially
high demand for calcium, obvious
ly, since each eggshell contains
about 2 grams (the weight of a
dime) of calcium. A dietary defi
ciency of vitamin D in egg-laying
hens results in osteomalacia (the
adult form of rickets), dwindling
egg production, and a deterioration
in eggshell quality.
Hoechstß
Roussel A
Lancaster Faming, Saturday, December 26, 1992-Al7
It is interesting that laying hens
are capable of producing substan
tially more 1,25-vitamin D than
non-laying birds (or mammals).
The most important consequence
of this is that calcium absorption
by the intestine is boosted by more
than twofold when an eggshell is
being formed. A few hours later,
when the egg has been laid,
amounts of 1,25-D return to lower
levels.
The discovery of 1,25-vitamin
D has led to new possibilities in
treating diseases of calcium meta
bolism, such as osteoporosis in
humans, milk fever in dairy cows,
and eggshell breakage in poultry.
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In birds in the wild, vitamin D is
obtained by preening the pro
cess of spreading oil from the
preen gland at the base of the tail
onto feathers so that the precursor
of vitamin D is exposed to sun
light In the commercial setting,
vitamin D is added to feed.
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