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Social
Class, Birth Weight Tied To Later IQ
Excerpt
By Suzanne Rostler, Reuters Health
NEW
YORK (Reuters Health) - A child's social class and weight at birth
are strong independent predictors of later intelligence, a new
study reports.
The number
of children a mother already had and birth to an unmarried mother
were also found to influence a child's IQ at age 11, according
to the report.
However, the
IQ of an individual child cannot be predicted by birth weight
or social class, cautioned Dr. Susan D. Shenkin, the study's lead
author, in an interview with Reuters Health. She noted that ``geniuses''
throughout history, including Albert Einstein, were small babies.
``The recommendations
to pregnant women to eat sensibly, stop smoking, breast-feed when
possible, and spend time with their children as they grow remain
unchanged,'' said Shenkin from the University of Edinburgh, Scotland.
The researchers
reviewed the birth records of 449 people born in two hospitals
in 1921 and examined scores from intelligence tests given at age
11. Test scores increased in tandem with birth weight, which was
estimated to account for nearly 4% of the variance in IQ. Social
class, which was not directly associated with birth weight, accounted
for nearly 7% of the variation in test scores, the investigators
report in the September issue of the Archives of Disease in Childhood.
But it is
not clear how birth weight and social class affect a child's later
intelligence, Shenkin and colleagues point out. According to one
theory, poor nutrition deprives a developing fetus of certain
nutrients during key stages of development, which can result in
low birth weight and changes in organs such as the brain.
Nutrients
including long-chain polyunsaturated fatty acids, iron, iodine
and zinc and hormones such as insulin-like growth factor are important
for normal growth, Shenkin told Reuters Health.
``Birth weight
is not in itself a direct influence on later intelligence but
rather a marker of influences such as poor nutrition or hormonal
stress on the developing child,'' she said. ``These influences
may have a long-term and permanent effect on the development of
the brain.''
The social
class of the parents is linked to the nutrient content of the
child's diet, breast-feeding (which is less common among lower
income groups), and opportunities for learning. Higher social
class is also linked to higher intelligence among parents, which
in turn has been shown to influence the IQ of their children.
The study
authors acknowledge that their findings, based on data from the
1920s, may not apply to today's children, since the importance
of early life influences may have changed. What's more, healthcare
today is significantly different than healthcare during the period
studied.
But the results
support those of more recent studies linking birth weight and
social class with intelligence. A report released in the past
month found that a child's weight at birth--even within the normal
range--was directly related to IQ at the age of 7 years. Numerous
other studies have shown that children and adults weighing less
than 5.5 pounds at birth fare worse on intelligence tests than
those who were heavier newborns.
``The fundamental
question all these studies endeavour to answer is whether the
cerebral impairment is prenatal or postnatal in timing and whether
environmental factors, of which social class is a surrogate measure,
have an important influence,'' Professor P.O.D. Pharaoh from the
Department of Public Health in Liverpool, UK, writes in an editorial.
``Possible
preventive and remedial measures will be dependent on the answers
to these questions,'' the editorialist concludes.
SOURCE:
Archives of Disease in Childhood 2001;85:189-197.
Reference
Source 89
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