Chemistry Reference
In-Depth Information
and eastern Europe) are typically iodine deficient (Zimmermann, 2006). In
goitrous children, iodine deficiency is exacerbated by inadequate intakes of
selenium, iron or vitamin A, or by consumption of goitrogens. Some goitrogens
are chemical agents (e.g., polychlorinated biphenyls, organophosphate pesti-
cides and dioxin) that can permanently alter the pituitary-thyroid axis if
exposure occurs during the perinatal period. Thyroid disruptor properties
have also been attributed to several plant-derived substances. Examples are
flavonoids, C-glycosylflavones (in millet), linamarin (from insufficiently
processed cassava leaves) and thioglucosides (from cabbage, Brussel sprouts,
broccoli and sorghum) (Fountoulakis et al., 2007).
The newest estimates of the iodine requirements for several age-sex
groups have been revised upward. For example, the iodine requirement for
infants aged 0-12 months are based on the current mean iodine intake of
American infants exclusively fed human milk (Table 10.2). The AI iodine
values established in 2001 for infants aged 0-6 months (110 mg/l) are much
higher than the RDA values established earlier for the same age group (40 mg/
d) (Food and Nutrition Board: Institute of Medicine, 2001). Likewise, the
iodine AI for infants aged 7-12 months was increased also (130 mg versus
50 mg/d). The estimate average requirement for iodine during lactation is
based on the average requirement of adolescent girls and non-pregnant
women (95 mg/d) plus the average daily loss of iodine in human milk
(114 mg/d). The RDA for iodine during lactation is 290 mg/d (Food and
Nutrition Board: Institute of Medicine, 2001). Data appear insufficient to
assess whether providing preterm infants with supplemental iodine (to match
fetal accretion rates) prevents morbidity and mortality in preterm infants
(Ibrahim et al., 2006).
Since 1990, the widespread introduction of iodized salt has greatly
reduced the global prevalence of iodine deficiency. However, the World
Health Organization recently estimated the worldwide prevalence of iodine
deficiency at nearly 2 billion individuals, of whom 285 million are school-aged
children (Zimmermann, 2006). Furthermore, the median iodine urine con-
centration (a standard indicator of iodine nutrition) has fallen in the United
States from 321 mg/l in the 1970s to 145 mg/l currently (Zimmermann, 2006).
The current average urine iodine concentration indicates adequate iodine
nutriture but a reminder of the importance of regular monitoring. Socio-
economic status is not necessarily a predictor of iodine sufficiency for the
general population. Despite the generally high standard of living in New
Zealand, the mean iodine concentration in breast milk of mothers living in
the South Island as late as 1998 and 1999 was 22 mg/l, a value only 15% of the
average US value (Skeaff et al., 2005). The prevalence of iodine deficiency is
the lowest (10.1%) in North and South Americas where the proportion of
households consuming iodized salt is highest (90%). Europe has the highest
