Chemistry Reference
In-Depth Information
prevalence of iodine deficiency (59.9%), and the proportion of households
consuming iodized salt is the lowest (27%). Most Europeans countries have
weak or non-existent national programmes for iodine supplementation
(Zimmermann, 2006). In Spain, almost half of pregnant women may have
iodine deficiency (Perez-Lopez, 2007). In some countries, ''silent iodine pro-
phylaxis'' occurs as improvements made in socioeconomic status allowed
easier access to imported food products richer in iodine. Ironically, this
approach sometimes has resulted in change of phenotypic expression of
thyroid disease from endemic goiter to goiter associated with autoimmune
thyroiditis from excessive iodine intakes (Fountoulakis et al., 2007).
Dietary iodine in the United States has generally been adequate since
the 1920s but median urinary iodine level, a biomarker for dietary iodine, has
decreased by over 50% from 1971 to 1994 among American women of child-
bearing age. However, The NHANES 2001-2002 data confirm the current
stability of the US iodine intake and continued adequate iodine nutrition for
the country (Caldwell et al., 2005).
Evidence supporting the protective effect of breast-feeding on the infant's
thyroid metabolism is overwhelming, and breast milk is the only source
of organic I, mostly thyroid hormones (T-4, T-3 and metabolites), in early
infancy (Dorea, 2007). The iodine concentration in both human and bovine
milks reflects maternal intake and thus are highly variable (see Table 10.1).
In the United States, average breast milk iodine concentration of mothers
is 146 mg/l. In countries with endemic IDD, breast milk iodine concentra-
tion is typically lower than 50 mg/l. Bovine milk is an important source of
dietary iodine. The iodine content in bovine milk varies linearly with
intake in the normal dietary range if other conditions are equal (Miller
et al., 1975). Iodine content also varies with the season (Dahl et al., 2003)
to the point that the incidence of thyrotoxicosis in Britain may be causally
related to the high milk iodine levels in winter-spring (Phillips et al.,
1988). In the United States, supplementation of animal feed with organic
iodine has increased the amount of iodine in bovine milk by 300-500%
between 1980 and 1986 (Food and Nutrition Board: Institute of Medicine,
2001). On the other hand, replacement of iodophors by other sanitizers in
the dairy industry is associated with a decrease in iodine content of bovine
milk and a re-emergence of iodine deficiency (Li et al., 2006).
Iodine enters bovine milk primarily as inorganic iodide, and iodine in
bovine milk, as naturally secreted, is only about 10% bound. About 16% of
total bovine milk iodine is in the cream but nearly all of the iodine in cream is
in the non-fat (serum) portion (Miller et al., 1975). Cream separation, pas-
teurization and spray-drying of milk appear not to affect the concentration
on a dry weight basis of either natural or iodophor-derived iodine in bovine
milk. Boiling apparently does not induce iodine volatilization significantly
