Agriculture Reference
In-Depth Information
affected child. Thus, folic acid supplementation is advised for all women “at risk”
of becoming pregnant. Fortification has been considered for this purpose, but this
means that the whole population receives considerably more folic acid than neces-
sary. Because folic acid and vitamin B
12
are so intimately related in terms of their
metabolic roles, giving excess folic acid can mask vitamin B
12
deficiency (discussed
in the next section). With our present knowledge, it would seem that fortification with
both vitamins is desirable. The argument about folic acid fortification still continues
in the United Kingdom. However, the United States and several other countries do
fortify flour, and the question now is whether the level of fortification is sufficient
(Brent and Oakley 2007).
Liver is an excellent source of folic acid, although the usual sources are dark
green leafy vegetables, beans, nuts, and milk. As folates are very susceptible to stor-
age, processing, and the like, fortification of cereals has become the norm for pre-
venting folate deficiency, particularly for women of childbearing age, as discussed.
Folate deficiency occurs in those on restricted diets (e.g., those living in poverty,
refugees) or in patients with malabsorption or who are unable to eat normally. It
is exacerbated by increased demand for new tissue synthesis, as in pregnancy and
infancy. Patients on antifolate drugs are also at risk, particularly those on long-term
treatment, for example, for epilepsy. The risk is even greater if pregnancy occurs.
Although anemia is the classical sign, hyperhomocystinemia occurs earlier and
should alert one to the need for supplementation. “Toxic” effects of folic acid excess
are limited to the indirect masking of vitamin B
12
deficiency. It may antagonize some
of the effects of antifolate drugs, but folate deficiency is more likely than toxic effects
from supplementation.
f
o L i C
a
C i D
s
t a t u s
Currently, erythrocyte folate concentration can be measured efficiently using
a radioligand-binding test. It reflects folate status over a few months, the average
life of a red blood cell. The formiminoglutamate (FIGLU) test, in which FIGLU is
metabolized by a folate-dependent enzyme, is a sensitive test of functional folate
status but is rarely indicated.
vItAmIn b
12
The core of vitamin B
12
is a cobalt atom within a corrin ring attached to various side
groups. It is absent from uncontaminated plant food but elaborated by bacteria and
present in animal tissues, especially liver (Geissler and Powers 2006). It is heat stable
so is not destroyed in cooking, unlike folates. Outright deficiency rarely occurs other
than in strict vegans. Unlike most essential nutrients, deficiency in the mother leads
to profound deficiency in the fetus; the fetus is not spared. Secondary deficiency,
however, is relatively common in patients with pernicious anemia or any other cause
of atrophic gastritis in which lack of intrinsic factor production by the gastric mucosa
prevents absorption of the vitamin in the terminal small intestine.
The early features of deficiency are due to loss of methionine synthase activity
as vitamin B
12
is its cofactor. Thus, the DNA cycle is impaired, and megaloblastic
