Breastfeeding Can Raise IQ

Tuesday 6 November 2007

Breastfeeding Can Raise IQ

Breastfeeding can have a positive effect on the IQ of children when combined with the right genes, according to a ground-breaking University of Otago study.

The findings, published this week in the journal Proceedings of the National Academy of Science, come out of the University’s Dunedin Multidisciplinary Health and Development Study.

Study Director Professor Richie Poulton says previous studies have shown that breastfed children average higher IQ scores than non-breastfed children.

“However, not all breastfed children show this higher IQ score. What we and our international collaborators have found is that they also have to have a certain version of a gene called FADS2.”

“We were able to rule out other potential explanations for the IQ findings, including the mother’s socioeconomic status and birth weight of the baby,” he says.

Researchers followed two groups of people: the 1000 Dunedin-born study members, and 2200 British children born in 1994-95. IQ of all study members was tested, and the mothers of study members were asked about breastfeeding practices.

The FADS2 gene is inherited from both the mother’s and father’s side. The gene comes in two versions: C and G. Children inherit either two of the “C” version, one each of “C” and “G”, or two of the “G” version.

The “C” version of the FADS2 gene is associated with more efficient processing of the omega-3 and omega-6 fatty acids found in breast milk. This may in turn help brain development and function, though the exact link is not yet known.

The researchers found that children with the “C” version of the gene averaged slightly higher IQ scores when breastfed as babies than those who were not breastfed. This IQ advantage was about 6 to 7 points.

Breastfeeding had no effect on children with two of the “G” version of the gene. IQ scores were neither advantaged nor disadvantaged.

“Their IQ was still in the normal healthy range,” says Professor Poulton.

In total, 90 per cent of the children studied had either one or two of the “C” version of the gene, and 10 per cent had two “G” versions of the gene.

Professor Poulton says that both genetic makeup and environmental factors are important.

“This shows that the argument is not nature versus nurture anymore. We’re finding that nature and nurture actually work together to produce health outcomes. This is true across all sorts of health areas, including positive outcomes like this study, and work involving mental health disorders.”

The research is supported by the Health Research Council (NZ), the National Institute of Mental Health (US), and the Medical Research Council (UK).

INFORMATION SHEET

Nature, nurture and the IQ: Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism

The Findings

Breastfeeding can have a positive effect on the IQ of children when combined with the right genes.

On average, Breastfed children have higher tested IQ scores than non-breastfed children. However, not every breastfed child shows this IQ advantage. The association between breastfeeding and children’s IQ depends in part on the genetic makeup of the child.

The Study

Researchers followed two groups of people: the 1000 Dunedin-born study members of the Dunedin Multidisciplinary Health and Development Study at the University of Otago, and 2200 British children born in 1994-95.

For this work, the IQ of study members was tested when they were children and their mothers were asked about breastfeeding practices. In addition, the FADS2 gene was tested from each study member’s DNA.

It was found that breastfed children with one or two ‘C’ versions of the FADS2 gene averaged an IQ advantage of 6 or 7 points over those children who were not breastfed.

Breastfed children with two ‘G’ versions of the FADS2 gene showed no IQ advantage or disadvantage over those children not breastfed.

Other explanations for this finding can be ruled out:

- The effect of FADS2 applied equally to babies with normal birth weight and low birth weight.
- High-social-class mothers are most likely to breastfeed, but the effect of FADS2 was the same in children from high-social-class and low-social-class homes.
- High-IQ mothers are most likely to breastfeed, but the effect of FADS2 was the same in children with high-IQ mothers and low-IQ mothers.
- We tested the study mothers’ DNA to see if the mother’s FADS2 genotype could have altered the quality of her breast milk to improve her child’s IQ. It did not.
- Children with the FADS2 ‘C’ genotype were no more likely to have been breastfed than children with the FADS2 ‘G’ genotype.

Why Is This Important?

For Society

For over a century, the intelligence quotient (IQ) has been at the heart of scientific and public debates about nature versus nurture. These findings show that genes may work via the environment to shape IQ.

For Public Understanding of Genetics

Research on gene-environment interaction has been dominated by searches for genes that increase susceptibility to diseases. As examples:
- people who carry the ‘short’ serotonin genotypes and who also suffer stressful life events are at a higher risk of depression.
- people who carry the ‘rapid’ NAT2 genotype and who also eat red meat are at increased risk of colorectal cancer.

But genes are not only relevant for disease. This study shows that a genetic variant (in FADS2) may also enhance a favourable response (enhanced IQ) to a healthy environment that has been present throughout human history (breastfeeding).

For Breastfeeding Advocates

There is controversy about whether breastfeeding is crucial for brain development. Specifically, there is healthy scepticism about whether breastfeeding really improves IQ, because science has not yet explained how breast milk could have an effect on the brain.

One hypothesis, which these findings support, focuses on the nutritional content of breast milk. Fatty acids in breast milk may be the raw material for a genetically-guided process that fosters optimal newborn brain development. Other lab experiments have shown that rodents and non-human primates fed diets deficient in fatty acids have abnormal brain development and learning difficulties, whereas animals fed fatty acid supplements have healthy brains and learn well. These findings help to link these animal experiments with information about human children.

The finding also adds that the link between breastfeeding and IQ is not a simple all-or-none connection.
It also depends to some extent on the genetic makeup of each infant.

For Infant Nutrition Researchers

Randomised controlled trials testing the effectiveness of formula supplements have yielded mixed results. This work suggests that “G” genotype babies in formula tests could wash out possible positive effects of fatty acid supplements, making effects difficult to detect.

For Gene Researchers

These findings show that scientists can use the environment to discover new genes that are important for human outcomes including diseases. The reasoning here began with breast milk, which led on to thinking about fatty acids, which led researchers to look for genes involved in the body’s use of fatty acids, which led to the FADS2 gene, which led to a promising marker of variation within the gene (rs174575). The chain of logic from environment to genetic marker allowed researchers to discover for the first time the link between the FADS2 gene and the IQ, an important child health outcome.

Background Information

How did we measure genotype?

Within the FADS2 (fatty acid desaturase 2) gene, there is a marker called “rs174575”. There are two versions of this marker in the human population, the ‘C’ and the ‘G’ alleles.
We tested for ‘G’ versus ‘C’ in each study member’s DNA. Children inherit one allele from their mother and one from their father, so can carry either two ‘C’ alleles, two ‘G’ alleles, or one each of ‘C’ and ‘G’. A ‘C’ allele enables the body to process fatty acids more efficiently. In this study, 90 per cent of the study members had at least one ‘C’ allele, and 10 per cent had two ‘G’ alleles.

How did we measure IQ?

The Dunedin-born study members were tested at ages 7, 9, 11 and 13 years of age. The British study members were tested at age 5. Each child was tested with the Wechsler
Intelligence Scales for Children (WISC), the gold standard of IQ tests. The average score on this test for the whole population of children is 100. An advantage of 6 or 7 points above 100 on this test places a child ahead of 66 per cent of all other children on the learning skills covered by the test. As this effect size is averaged across hundreds of children, each individual child’s IQ could be higher or lower.

How did we measure breastfeeding?

Mothers were asked about breastfeeding when the children were aged 1 to 3 years. In the Dunedin cohort, 57 per cent of children were breastfed. When these children were born in 1972-73, those not breastfed were given formula prepared from powdered cow’s milk. 48per cent of the British cohort were breastfed. When these children were born in 1994-95, formula supplementation with fatty acids was not widely available in the UK.

Limitations of the Study

The study is currently limited to two countries: the UK and New Zealand. Scientific findings only gain trustworthiness after they are repeated by different teams, and so this study needs to be repeated by other teams in other countries.
The precise mechanism by which variation in the FADS2 gene guides processing of breast milk nutrients to alter brain development has not yet been worked out. It is already known that individuals with different FADS2 genotypes process fatty acids more or less efficiently, but exactly how they do this is not clear yet.

It is unlikely that FADS2 is the only gene involved. Breast milk contains many different nutrients and many genes are likely to be involved in processing them.

Publication Source

Proceedings of the National Academy of Sciences
Authors:
Avshalom Caspi, B Williams, J Kim-Cohen, IW Craig, Barry J Milne, Richie Poulton, LC Schalkwyk, A
Taylor, H Werts, & Terrie E Moffitt

Universities/Institutions

Dunedin Multidisciplinary Health and Development Research Unit, Department of Preventive and Social
Medicine, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
Medical Research Council Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry,
King’s College, London, UK
Departments of Psychology & Neuroscience, Psychiatry & Behavioral Sciences, and Institute for Genome
Sciences and Policy, Duke University, Durham, North Carolina, USA
Department of Psychology, Yale University, Connecticut, USA
Funding Agencies
Health Research Council (NZ)
Medical Research Council (UK)
National Institute of Mental Health (USA)
Royal Society-Wolfson Research Merit Award (UK)

ENDS

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