Scientists at the University of Bristol have shown that there appears to be a link between the growth hormone IGF-I and the child’s IQ. The findings could explain why some shorter children do worse at school.
The study is based on 547 children who completed an intelligence test at the age of 8.
Professor David Gunnell and his colleagues measured levels of the Insulin Growth Factor IGF-I in their blood.
Circulating levels of insulin-like growth factors are influenced by a variety of factors, including our diet, and control the effects of growth hormone on tissues and play a key role in physical growth and organ development in childhood
Professor Gunnell says it well known that babies of low birth weight are slower to develop.
“Poor fetal and post-natal growth are associated with impaired neurodevelopment. Low birthweight babies experience delays in reaching motor milestones and on average have slightly lower IQs than normal weight babies.”
“Similarly, short stature – a measure of poor post-natal growth and nutrition – is associated with low scores in tests of cognitive function and poor educational achievement.”
“To the best of our knowledge, this is the first study to investigate the association of IGFs with measures of intellectual performance in population samples of normal children.”
So far, scientists don’t know what actually happens in the body to link poor growth and impaired neurodevelopment, although one explanation could be that growth hormones may also affect development of the brain.
When they compared IGF-I levels, researchers found a significant link with intelligence. For every 100 nanograms per millilitre increase (100ng/ml), IQ increased by 3 points. The effect seemed to be restricted to the verbal component of IQ and was not seen in other tests.
Professor Gunnell says:” This study provides some preliminary evidence that IGF-I plays an important role in human brain development and may underlie the associations of birth weight and height with IQ.
“Further support for this association comes from a recent study in which 74 low birthweight children were treated with Growth Hormone therapy and followed up for over 2 years. The therapy led not only to improved growth but also to improvement in IQ”
The association of IGF-I and IGFBP-3 with IQ in 8-9 year old children in the Avon Longitudinal Study of Parents and Children. David Gunnell , Laura L Miller , Imogen Rogers, Jeff MP Holly and the ALSPAC team. Pediatrics 2005