Page 25 - summer2016

teratogenic effects from exposure to excess pre-
WIDESPREAD DEFICIENCY formed vitamin A in the first trimester, vitamin
Since the fetal liver is only able to store a small amount of vitamin A supplementation in pregnant women who are
A, it is generally accepted that almost all babies are born with marginal not deficient is not recommended.” Yet, these
vitamin A deficiency. “Even term infants are relatively deficient in vi- same authors add “women with low vitamin A
tamin A at the time of birth compared to older children.” Premature intake or reduced liver stores should increase
54
infants have even lower liver stores of vitamin A at birth and their blood their intake throughout pregnancy to ensure
concentrations of retinol often remain low throughout their first year, adequate stores are available for rapid fetal
putting them at risk for eye, chronic lung and gastrointestinal diseases. 55 growth in late gestation.”
22
Vitamin A supplementation in pre-term infants reduces mortality and
oxygen requirement and is considered a promising intervention for ASSESSING VITAMIN A STATUS
bronchopulmonary dysplasia prevention, a lung impairment common to Assessing vitamin A status is difficult. 1
preemies. Measuring liver reserves using a biopsy is
56
Other scientists have expressed their concerns. “The fetus begins considered the gold standard but this procedure
accumulating vitamin A during the third trimester and needs several is highly invasive and thus very rarely used.
months of sufficient intake after birth to build up an adequate store. The Clinical signs like poor dark adaptation, xeroph-
composition of breast milk is influenced by the vitamin A status of the thalmia (dry eyes), hyperkeratosis (hard bumps
mother during the last trimester. “[T]he main consequence of a poor on skin), or even acne in adult women can yield
vitamin A supply during pregnancy is a low vitamin A status at birth clues, but the absence of these signs cannot rule
and in the next few months.” out deficiencies. Night blindness is not likely
59
1
The vitamin A content in the breast milk of mothers who deliver to occur until liver stores are dangerously low.
prematurely is often closer to mature breast milk (which comes in three to Assessing intake not only requires detailed
four weeks after delivery). Both contain one-tenth to one-half the amount dietary records over several days (especially
of vitamin A in the earliest milk, colostrum. Is there a connection between since people don't eat liver very often) but also
a deficiency of vitamin A in a premature infant and the lower content information on whether a woman is a good or
of the mother’s milk—perhaps an indication that the mother herself was poor converter of beta-carotene into retinol.
deficient in vitamin A? Liver stores can be estimated using the relative
These findings pose serious questions. The first is, why are newborns dose response test (RDR or MRDR): blood is
(even in developed countries) born with low or depleted stores of vitamin drawn, a dose of vitamin A is given, then the
A? Secondly, since experts know vitamin A is necessary, why are there change in serum retinol is measured five hours
so many warnings against it and why don’t prenatal vitamins contain it to later; an increase of 20 percent or more usually
any degree? Finally, if the mother’s vitamin A intake has little effect on indicates deficient liver stores of vitamin A. This
her newborn’s vitamin A levels, why do newborns in developing coun- test has been used for population assessment but
tries have even lower amounts in their bodies compared to the developed appears to be uncommon in clinical settings.
59
world? One surmises that the widespread prevalence of maternal vitamin Measuring blood levels of vitamin A is the
A deficiency in these countries may be a primary reason. Although stores more common way of determining vitamin A
of retinol in the livers of human fetuses have been found to be lower than status. In healthy adults, the plasma vitamin
those of adults, significant correlations have been measured between A concentration ranges from 20 to 80 μg/L.
60
maternal serum retinol, fetal liver retinol and fetal growth. 57 However, blood levels can remain normal even
In adults, vitamin A stores are used up daily, at the rate of about 0.5 when liver, lungs and other organ stores are low.
percent per day. This could occur more rapidly for those with lower liver Blood levels drop below the normal level of 20
stores, which depend on dietary intake. Vitamin A depletion could be μg/L only after liver stores are exceedingly low,
58
accelerated during times of higher demand, such as infection or periods so marginal liver stores may not be detected. A
of rapid growth, which is why children’s dietary requirements are almost result of 10 μg/L indicates a severe deficiency
the same as adults. With little or no preformed vitamin A intake during a and depleted liver stores.
61
full-term pregnancy of about two hundred seventy days, an almost total To determine either deficiency or excess
reduction in liver stores after two hundred days is theoretically possible. states, measure both serum retinol (or serum
Does conventional obstetrical care ever recommend vitamin A for vitamin A) and serum retinyl esters (serum A
“healthy” women? palmitate); serum retinol should ideally be in
According to a medical nutrition textbook, “because of the potential the middle or upper half of the reference range
Wise Traditions SUMMER 2016 Wise Traditions 25