Page 23 - Spring2009

if vitamin A is in short supply, on the other A will damage the liver and contribute to an imbalance of cell signaling.
hand, the results can be detrimental. By “stealing” If vitamin D is present in excess, extra vitamin A is needed to fulfill
all of the vitamin A needed to use for vitamin D- those other functions, while if vitamin D is in short supply, the natural
specific functions, the body will not have enough balance of functions in which vitamin A engages may be thrown off.
vitamin A left to support the many other functions The current controversies over osteoporosis present a perfect example
for which it is needed—this may partially explain of how critically important it is to take into account the interactions between
the toxic effects of excess vitamin D. these two vitamins. A number of studies have shown that high intakes of
vitamin A toxicity is likely due in part to the vitamin A are associated with reduced bone mineral density and increased
damage done to liver cells and the release of their risk of hip fracture, but these studies have been conducted in populations
contents, including storage forms of vitamin A, with vitamin D intakes as low as 100 iU per day. The only study that men-
into the blood. it may also be the case that there tioned cod liver oil as a source of vitamin A in its population found high
is a natural balance between the many different levels of vitamin A to be associated with a decreased risk of fracture. it
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signaling roles played by vitamin A when all of may be the case that vitamin A contributes to osteoporosis when vitamin D is
its signaling partners are present, but that when deficient, but protects against osteoporosis when vitamin D is adequate.
one of them—such as vitamin D—is absent, this A review published in 2005 concluded that physicians should explicitly
natural balance is thrown off. Thus when vitamin warn their elderly patients to avoid intakes of vitamin A greater than the
D is provided in adequate amounts, vitamin A rDA. A large-scale, placebo-controlled trial published in 2006 found that
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does not accumulate excessively in the liver and 400 iU of vitamin D plus 1,000 milligrams of calcium increased the risk
this natural balance is maintained, but when vi- of kidney stones by 17 percent. Kidney stones can be induced by feeding
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tamin D is in short supply, high doses of vitamin animals vitamin A-deficient diets, and prevented in animals by feeding
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DOeS VITAMIn A IncReASe THe RISk Of InfecTIOnS?

Cannell cites an analysis in his journal article and December newsletter as showing that vitamin A supplements de-
crease lower respiratory infections “in children with low intake of retinol [vitamin A], as occurs in the Third World” but that
“it appears to increase the risk and/or worsen the clinical course in normal children.” By the time Mercola published the
1,2
claim, “normal children” became any children living in a developed country. “Unlike third world countries where vitamin
A supplementation appears to decrease infections,” Mercola wrote, “vitamin A supplementation in developed countries
like the U.S. actually increases infections.” 3
The original analysis did not present any findings that separated children into low and normal intakes of vitamin A and
did not include any studies conducted in developed countries like the United States. It was a meta-analysis that pooled
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the results of nine studies conducted in India, Ecuador, Indonesia, Brazil, Ghana, Mexico, and the Republic of Congo.
Several of these studies have suggested that vitamin A may reduce the incidence of respiratory infection in malnourished
children but increase it in well-nourished children. none of them, however, present evidence that the effect of vitamin A
depends on vitamin A status or that vitamin A is helpful in the third world but harmful in the developed world.
An Ecuadorian study of four hundred children under the age of three found that weekly supplements delivering roughly
half the RDA for vitamin A reduced the risk of lower respiratory infections among underweight and stunted children but
raised the risk among children of normal weight and height. An Indonesian study of over 1400 children under the age of
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four found that three massive doses of vitamin A given over the course of a year, likewise delivering roughly half the RDA,
increased lower respiratory illnesses in children of normal height but not in stunted children. Although both of these studies
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measured blood levels of vitamin A, neither of them reported the effect of vitamin A to be dependent on vitamin A status.
They were conducted in areas where deficiencies of protein, energy, and multiple vitamins and minerals are common. A
child’s status of protein, zinc, vitamin D, and other nutrients will affect his or her metabolism of vitamin A. Growth status
itself could affect the metabolism of vitamin A, and adequate growth could deplete other nutrients needed for vitamin A
to function properly.
It would also be a mistake to look at lower respiratory infections alone. A number of studies included in the meta-
analysis showed vitamin A to have no effect on respiratory infections while nevertheless reducing severe diarrhea by over
20 percent, gastrointestinal-associated mortality by over a third, infection-associated mortality by half, and measles
14
15
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incidence by 95 percent. 16,17 The general picture that emerges from the scientific literature is not that vitamin A is helpful
only in very small amounts and harmful in larger amounts. The picture that emerges indicates that vitamin A consistently
reduces mortality from severe infectious diseases but has a more complicated relationship to lower respiratory infections
that we still do not completely understand.
SPRING 2009 Wise Traditions 21