The Effect of Infant Growth on Intelligence

Recent research indicates that one of the key factors influencing intelligence is infant growth, both in the womb and in the first year of life. Evidence seems to show that babies with better growth and, in particular, larger heads develop greater intelligence as children, leading possibly to better success in life as adults.

Bigger Babies, Brainier Adults?

Older studies have long shown that low-birth weight babies (weighing less than 2.5 kg or 5.5 pounds at birth) are at risk of poor intellectual development. Recently, a new study has found the same link in normal birth weight babies. Researchers followed over 5,000 babies, born during the same week in Mar 1946, throughout the course of their lives, tracking data such as their physical and psychological health, while also applying specific intelligence tests at certain ages – for example, reading comprehension, word pronunciation, vocabulary, verbal reasoning at age 8, verbal and non-verbal intelligence, reading comprehension, mathematics at age 15 and verbal memory, timed letter search at age 43. The results were corrected against other factors that might affect intelligence, such as birth order, sex differences, mother's education and age, and father's social class. The results show that bigger babies definitely had an advantage. For example, the heavier babies were already showing higher scores in the first tests, at age 8. However, as the individuals aged, their original advantage decreased so that by age 43, they no longer showed a significant advantage in test scores. This may possibly be because the initial benefit of higher birth weight is gradually erased by environmental influences, ie. other things that affect cognitive function, such as education, occupation and health. Researchers believe that the advantage may come from the fact that the growth factors which produce larger babies also target the areas of the brain that are important for cognitive function.

Why it’s Good to be Big-Headed

While bigger in general is better, all other things being equal - the most benefit seems to come specifically from bigger heads and hence larger brains. In another study, children with the largest heads scored the highest in IQ tests, leading researchers to believe that the brain volume that a child achieves by the age of one helps to determine later intelligence. However, the key was growth of the head before the age of one – growth thereafter seemed to have little effect on intelligence. In fact, brain growth after infancy did little to compensate for poor growth in the first year of life. Naturally, several other factors also play an important role in developing intelligence – for example, the children tended to have higher IQ scores if they had been breastfed for more than 3 months, if their parents were better educated and if their mothers scored high on the parenting questionnaire. Nevertheless, even adjusting for these factors, the children’s head growth in the first year of life remained significantly linked to later IQ.

Growth in the Womb

Intrauterine growth also plays an important role in developing intelligence. For example, one of the consequences of foetal alcohol exposure, which restricts foetal growth and damages the central nervous system, is dysfunction which may affect intelligence, learning and memory, activity and attention, language and motor abilities, and behaviour. In a study of twins, it was found that intrauterine growth retardation may have long-term effects on the growth and development of the children, in particular the eventual height, head circumference and performance IQ.

Grow Your Babies Well

In summary, to help your baby achieve his intellectual potential, it would do well to eat well during pregnancy and to avoid any activities which may impede growth in the womb, so that your baby is born with a good birth weight – followed by good growth, especially in the first year of life. However, for the many anxious parents with “small” children out there, remember that intelligence is a very complex, multi-faceted phenomenon and birth weight, head size and growth rate are simply some of the things that can influence cognitive development. For example, the effect of birth weight on intelligence can be easily compensated by parental involvement in education. Lastly, remember that there numerous examples of “small people” with high intellectual achievements and success in life.