Early nutrition, brain structure and IQ

Wednesday February 20 2008

“Premature babies given a diet richer in proteins have higher IQs as adolescents”, The Times reports. Other newspapers also report on a study on premature babies fed protein-rich milk in the first four weeks after their birth, who had greater IQ scores as children and as adolescents. The Guardian reports that the early diet not only affected IQ scores, but also “the size of the structure in the brain that has been associated with IQ”.

This study used some of the participants and data from a previously published study on nutrition and cognitive function in children born prematurely. The current study is small as it only followed up some of the original participants. It also has several other important limitations: it was initially set up for a different purpose, and did not originally aim to investigate an association between protein intake and IQ.

Although it is likely that premature babies are vulnerable to less-than-optimal nutrition, these findings need to be supported by findings from large robust studies. From the results of this study, it is not possible to draw scientifically sound conclusions about the significance of any direct relationship between diet and IQ.

Where did the story come from?

Dr Elizabeth Isaacs and colleagues from the University College London Institute of Child Health, and Great Ormond Street Hospital for Children in the UK, and the Harvard Medical School, New York University, and Massachusetts Institute of Technology in the US carried out the research. The study was funded by The Medical Research Council and The Wellcome Trust in the UK, and by various other sources in the US. The study was published in the peer-reviewed medical journal: Pediatric Research.

What kind of scientific study was this?

In this most recent study, the researchers included some of the participants from a previously published randomised controlled trial of premature infants born in the 1980s.

In the original study, premature infants were assigned to either standard-nutrition (donor breast milk or standard formula feed for term infants) or high-nutrition (specifically formulated to meet the nutritional needs of premature infants and with higher protein content than the standard diet) for one month after birth. The aim of this study was to see whether nutrition affected cognitive function when the premature children reached about eight years of age.

For this recent study, the researchers wanted to see what effect early nutrition has on brain structure, and in particular the caudate nucleus. This is an area believed to be involved with movement, learning and memory and its size can relate to IQ. The researchers wanted to test the theory that “growth restriction of the caudate nucleus might, at least in part, provide a potential mechanism for the observed nutritional effects on IQ.”

To do this, the researchers selected 76 children from the original study (who were now an average of 16 years old), who had been born with a gestational age of 30 weeks or less and had had normal findings on neurological examination. This amounted to 34% of the original standard-nutrient group and 32% of the high-nutrient group. Further IQ tests and MRI scans were then carried out by an examiner who was unaware of the original diet of the participant. Total brain size and that of the various brain structures were determined by MRI scan.

The researchers investigated whether there were any differences in the children’s IQ, brain size or brain structure according to their diet as a premature infant. Efforts were made to take into account any differences in birth weight and the number of weeks of prematurity that existed between the groups (the high-nutrient group had on average a slightly higher birthweight and five days' longer gestation). Maternal education, social class and complications or infections around the time of birth were all found to be similar between the two groups. The researchers also collected IQ data and brain scans from a small comparison group of 16 full-term infants to act as a comparison.

What were the results of the study?

At adolescence, verbal IQ scores were significantly greater in the high-nutrient group than those of the standard-nutrient group. However, there was no difference between the groups in performance IQ.

There was no difference between the groups in the size of any of the brain structures measured by MRI scan (including total brain volume). The exception to this was the caudate nucleus, which had significantly greater volume in the high-nutrient group compared to standard nutrition.

When both groups were combined, it was found that verbal IQ, but not performance IQ, appeared to be related to the size of the caudate nucleus. However, when the groups were analysed separately, statistical significance remained only with the standard group.

When the researchers looked at boys and girls separately, there was no statistically significant difference in IQ scores between the high and standard groups among either sex. However, while the girls had no difference in caudate nucleus size between the high and standard groups, the boys' caudate nucleus size was significantly greater in the high-nutrient group.

There was no relationship between IQ and caudate nucleus size in the 16 full-term adolescents examined.

What interpretations did the researchers draw from these results?

The authors conclude that "for the group as a whole, differences in early diet were associated with significant differences in verbal IQ but not performance IQ at adolescence". In support of their theory, they say that the "experimental intervention was associated with larger left and right caudate volumes in those fed the high-nutrient diet".

What does the NHS Knowledge Service make of this study?

Few studies have attempted, as this one does, to show how the structure of the brain can be influenced by nutrition in early life, and caution is needed when interpreting these results:

  • Because of the study design, the findings cannot be extended to the original groups of children. The original study was also not designed to see if improved early nutrition increases IQ.
  • The current researchers only selected 76 of the original cohort of premature babies (originally 424 infants). They restricted their sample to those with a gestational age of less than 30 weeks and who had normal neurological findings at their 7-8 year follow-up, and who were available for imaging at the age of 16. This amounted to 34% of the original standard-nutrient group and 32% of the high-nutrient group. Had those with neurological problems been included, the findings may have been different. They may also have been different if all children in the original study had been followed up to age 16. The authors report that they also were not able to carry out scans for some of the participants due to travel difficulties.
  • Many other factors that can affect a child’s IQ have not been accounted for; such as education, home environment, diet and lifestyle, and genetic inheritance. Future studies also need to look in more depth at full-term infants as they have not been thoroughly examined here.
  • There is also a considerable difference between a protein-rich milk diet given in just the first four weeks of life and a high-protein or nutrient diet throughout childhood or adult life. In addition, the feeds given to premature babies in the 1980s may differ from those available now.

Although common sense and current scientific understanding indicates that a healthy diet is the best way to start out in life, this particular study does not assess, or indicate, how early diet relates to intelligence.

Sir Muir Gray adds...

The smaller the person – the more important the quality of care. For the premature every hour is important.

Analysis by Bazian
Edited by NHS Choices