Agriculture Reference
In-Depth Information
with socioeconomic status (Grantham-McGregor et al. 1999). Two reports from
developing countries suggest a complicated relationship between development and
breastfeeding. In Chile, exclusive breastfeeding for under 2 months or more than 8
months was associated with poorer mental and motor outcomes at 5½ years (Clark
et al. 2006). Another report from Honduras indicated that infants who were exclu-
sively breastfed for 6 months crawled sooner and were more likely to be walking at
12 months compared with infants exclusively breastfed for 4 months when additional
high-quality, complementary foods were also offered (Dewey et al. 2001). These
studies require replication before firm conclusions are drawn.
Other problems with the studies included variation in the definitions of
breast-
feeding
(e.g., definitions depending on the duration and exclusivity of breastfeeding),
small sample sizes in some studies, and observers were not always blind to the par-
ticipants' status (Drane and Loggeman 2000).
Despite the problems with the studies, some reviewers have argued that the con-
sistency of the findings suggest that a small benefit to cognition from breastfeeding
is likely (e.g., Grantham-McGregor et al. 1999, American Academy of Pediatrics
2005). Uauy and Peirano (1999) concluded that while high-quality scientific research
should be demanded before accepting findings, the suggestive positive results should
be taken into account for policy recommendations. The additional 2 to 5 IQ points
would be a small difference for individuals but may be of great importance at a
population level.
IodIne
Iodine deficiency can lead to cretinism and irreversible mental retardation (Black
2003b) and is the most common preventable cause of mental retardation. A global
program to reduce iodine deficiency primarily through salt iodization has had sub-
stantial success; nonetheless, iodine deficiency continues to threaten the develop-
ment of children in many parts of the world.
Iodine is a constituent of the thyroid hormones thyroxine and triiodothyronine,
which influence the development of the central nervous system (Pharoah and Connolly
1995). Maternal iodine deficiency during pregnancy affects brain development in
utero (Hetzel and Mano 1989), and deficiency in infancy and early childhood may
also affect development.
In addition to the most serious effects of cretinism, iodine deficiency in the sub-
clinical range can also affect mental development. Studies comparing children living
in iodine-deficient areas with those living in iodine-sufficient areas have generally
shown children in iodine-deficient regions to have lower cognitive development and
school achievement. In a 1994 meta-analysis of 18 studies, IQ scores averaged 13.5
points lower in iodine-deficient groups (Bleichrodt and Born 1994). A second meta-
analysis of 37 studies reported a very similar deficit of 12.5 IQ points (Qian et al.
2005). However, communities with iodine-deficient soil are often more isolated and
poorer. In a study adjusting for possible confounding factors, subclinical prenatal
iodine deficiency remained associated with poor infant development (Choudhury
and Gorman 2003).
