Page 22 - Spring2009

They a treatment, it reduced mortality from this disease toxicity of the other. 18,19,20,21 This observation
concluded by the same amount. 8 held true even when the vitamins were injected
into the animals rather than provided in the diet,
that while viTAMin A AS An AnTi-infeCTive showing that they did not protect against each
vitamin D in the 1920s, edward Mellanby performed a other’s toxicity by competing for intestinal ab-
22
was necessary series of experiments at the University of Shef- sorption.
field showing that vitamin A was the primary
To explain the earliest observations of this
for the anti-infective component of cod liver oil. Mel- phenomenon, the german researcher f. Thoenes
calcification lanby compared the effects of cod liver oil, rich proposed in 1935 that vitamins A and D cooper-
of bones and in vitamins A and D, to those of butter, rich in ated with each other to perform certain functions
vitamin A only, and to those of olive oil, deficient and that vitamin D caused toxicity by inducing a
teeth, it did in both vitamins. Dogs fed butter instead of cod relative deficiency of vitamin A. This concept
23
not share the liver oil had soft bones and partially collapsed gained further support in 1998 when Aburto
anti-infective lungs, but bronchial pneumonia occurred only on and Britton showed that even moderate doses of
the olive oil diet. Mellanby attributed the partial vitamin D lower blood levels and liver stores of
properties collapse of the lungs to muscular dysfunction in- vitamin A in broiler chickens whether they are
of vitamin A duced by vitamin D deficiency and attributed the provided in the diet or by exposure to ultraviolet
24
and it would pneumonia to degeneration of the epithelial lining light.
of the lungs induced by vitamin A deficiency.

Developments in molecular biology over the
9
therefore be When pure vitamin D became commercially last several decades have shown that vitamins A
2
dangerous to available, Mellanby and his colleague harry and D carry out most of their actions by binding
replace norman green performed further experiments to specific receptors that will bring them into
in rats showing that vitamin A deficiency led to contact with DnA inside the nucleus of a cell, in
traditional often fatal infections of the tongue, throat, eyes, order to alter the expression of genes by turning
cod liver oil lungs and gastrointestinal tract in nearly all of the them on or off or by turning them up or down.
with the animals. In several hundred vitamin D-deficient The receptors for these vitamins, together with
rats, by contrast, they observed only two cases of those for thyroid hormones, steroid hormones,
newly infection. In the vitamin A-deficient rats, more- and other important signaling molecules, are part

developed over, vitamin D supplementation made the infec- of a common family of nuclear receptors that
vitamin D tions worse. green and Mellanby suggested that interact with one another. vitamin A is especially
this was because vitamin D stimulated growth involved in these interactions—it not only car-
supplements. and “thereby made a greater call on the vitamin ries out its own signaling, but forms an essential

A stores of the body.” They concluded that while partnership with most other nuclear hormones,
vitamin D was necessary for the calcification of which allows them to carry out their functions.
bones and teeth, it did not share the anti-infective recent research, described in more detail in the
properties of vitamin A and it would therefore be sidebar on page 22, has shown that vitamin D can
dangerous to replace traditional cod liver oil with only effectively control the expression of genes
the newly developed vitamin D supplements. “if in the presence of vitamin A.
a substitute for cod-liver oil is given,” they wrote, Since vitamin A is required as a signaling
“it ought to be at least as powerful as this oil in partner with vitamin D, vitamin D will increase
its content of both vitamins A and D.” 9 the turnover of vitamin A. if vitamin A is provid-
ed in excess, the results are generally beneficial.
viTAMinS A AnD D excess vitamin A is stored in the liver. however,
AS MoleCulAr PArtnerS when the liver’s storage capacity is exceeded, the
Mellanby was correct when he noted that overload of vitamin A causes the cells to burst,
vitamin D increases the need for vitamin A, but damaging the liver and releasing storage forms
he was probably wrong about the mechanism. of vitamin A into the systemic circulation that do
Beginning in the 1930s and continuing through not belong there. By increasing the utilization of
the 1960s, research accumulated showing that vitamin A, vitamin D can help prevent vitamin A
vitamins A and D each protected against the toxicity.
20 Wise Traditions SPRING 2009