Baby Brains and Breastfeeding: The effects of exclusive breastfeeding on cognitive development

The correlation between exclusive breastfeeding and intelligence or cognitive development has been observed in many studies.  Some infants who were breastfed exclusively were shown to have an advantage over non breastfed infants in terms of intelligence quotient (IQ).  Overall trends seem to identify a correlation; however there are many confounding factors involved that are inherent in this study.  Maternal IQ, maternal age, maternal race and socioeconomic status all have been shown to have an effect on the intelligence of the children studied.  In most studies, maternal factors have been disregarded; however it is difficult to eliminate all of these factors in a single study.

Breastfeeding gives infants a definite advantage in terms of nutrition, attachment and bonding, however it has yet to be linked exclusively to intelligence later on in life.  One area of study is the effect of the fatty acid Docosahexaenoic acid (DHA) on the developing brain of infants.  It is known that DHA is present in human milk, and not present in cow’s milk nor in infant formulas (the DHA in infant formula is plant based and more difficult to absorb in the body when compared to that of the DHA in  human milk).  In the following literature review, I will try to decipher if the research shows a significant link between the length of exclusive breastfeeding and intelligence.

The five studies discussed herein have are longitudinal surveys that have been performed in five different countries: Poland, England, Australia, United States and New Zealand.  Direct links to these articles will follow this review.  The term exclusive breastfeeding means that the infant was only fed human milk for the reported duration of time: in this case; 3 months, 4-6 months or >6 months.  The child was not given any other form of food during the first 6 months of life, including water or table foods.

It is interesting to note that there are no agreed standards of measure in this area of human development.

Discussion:

The Effect of Breastfeeding on intelligence in children: prospective study, sibling pairs analysis and meta-analysis.  Geoff Der, G David Batty, Ian Deary.

This longitudinal study surveyed a group of females aged 14-22 beginning in 1979 annually and ending in 1994.  After 1994, the women were surveyed biannually and their children’s cognitive ability was measured from 1986-2002.  The children’s home environment, demographics and maternal characteristics were also measured.

Most of the association between breastfeeding and cognitive development was found to be the result of maternal intelligence.  Therefore this study has found that there is a stronger link between maternal intelligence and the child’s IQ, rather than a direct link to the effects of exclusive breastfeeding (in full term infants).

Confounding factors in this study were found to be of higher correlation to intelligence.  These factors are IQ and race of the mother.  “Hispanic mothers were less likely to breastfeed their children and black mothers were much less likely” (Der et al., 946).  Maternal IQ more than doubled the odds of breastfeeding.    This study failed to make a direct and significant connection to the hypothesis that breastfeeding promotes intelligence in full term infants.  However the researchers do not deny that breastfeeding “remains an unequalled way of providing ideal food for the health and growth and development of infants” (Der et al. 948).

Effect of exclusive breastfeeding on the development of children’s cognitive function in the Krakow prospective birth cohort study

Wieslaw Jedrychowski, Frederica Perera, Jeffry Jankowski, Maria Butscher, Elzbieta Mroz, Elizbieta Flak, Irena Kaim, Ilona Lisowska-Miszczyk, Anita Skarupa, Agata Sowa

This is also a longitudinal study showing the association between the cognitive achievements of preschool aged children who were exclusively breastfed as infants for given periods of time.  Major confounding factors are similar to the Der et al. study.  However this research study has concluded that children who were exclusively breastfed for 3 months had an IQ 2.1 points higher than those who were not exclusively breastfed, those exclusively breastfed for 4-6 months had an IQ 2.6 higher and those exclusively breastfed for greater than 6 months were found to have an IQ 3.8 points higher.  They also found that breastfeeding had beneficial results in the cognitive development even for a short duration of time.

A confounding  factor found in this study was found to be that the mothers of the children most likely to have been exclusively breastfed were better educated and had other children and gained less weight during pregnancy; indicative of better maternal nutrition and perhaps better overall health.  An increase in the duration of exclusive breastfeeding was “accompanied by a gradual increase in cognitive developmental score.  Moreover it was shown that the breastfeeding effect on children’s IQ trajectory was consistent and stable over the entire follow-up period” (Wieslaw et al.).  Furthermore, the influence of maternal characteristics are considered insignificant past one year of age, and therefore further support the hypothesis that infants who are fed only human milk for the first 6 months of life are given a better basis for the development of cognitive ability and function.

The effect of breastfeeding on child development at 5 years: A cohort study

PJ Quinn, M. O’Callagnan, GM Williams, JM Najman, MJ Andersen and W Bor

One focus of this study is the effect of the fatty acid DHA on a child’s cognitive development.  Human milk contains high levels of DHA and other “bioactive components essential to the brain development of infants” (Quinn et al.)  DHA is present in human milk and absent in cow’s milk and engineered infant formula.  The children who were exclusively breastfed for up to 3 months scored an average of 4-5 points higher on all psychometric tests when compared to those infants who were not.  Data derived from this study confirmed that children who were fed a mixture of formula and breastmilk achieved lower total IQ scored than those who were fed breastmilk exclusively.  Generally, it was found that an increase in the duration of breastfeeding correlated to a higher score on cognitive tests.  This may also suggest that early breastfeeding sets children higher on IQ scores and has a long lasting effect on cognitive ability into adulthood (Quinn et al.)

Moderation of breastfeeding effects in the IQ by genetic variation in fatty acid metabolism

Avshalom Caspi, B Williams, J Kim-Cohen, I Craig, B Milne, R Poulton, L Schalkwyk, A Taylor, H Werts, T Moffitt.

This study furthers the connection between the presence of fatty acids DHA and arachidonic acid (AA) in breastfed children and their higher IQ scores.  Infants who were exclusively breastfed were found to have higher levels of both DHA and AA when compared to infants who were formula fed.  “In humans, children who are breastfed have higher IQs than children not fed breastmilk and this advantage persists into adulthood” (Caspi et al.)

Confounding factors that were ruled out in this study include socioeconomic status, social class and maternal IQ.

The findings of this research has “implications for neuroscience and early child development as human milk is widely promoted as good for the brain, and further the assumption that DHA and AA may be needed for optimal intellectual development” (Caspi et al.).

Breastfeeding and intelligence of preschool children

RF Slykerman, JMD Thompson, DMO Becroft, E Robinson, JE Pryor, PM Clark, CJ Wild, EA Mitchell

The aim of this study is to investigate whether breastfeeding during infancy is a determinant of intelligence measured at 3.5 years of age.   A main component of this study has been noted that few studies successfully rule out potential confounding factors or use standardized measures of intelligence.  They also suggest that most previous studies involve full term average weight infants.  They focus their study on full term infants who are small for gestational age (SGA).  They found that “breastfeeding is significantly associated with higher intelligence test scores at 3.5 years of age in children who were small for gestational age at birth” ( Slykerman et al. 836).  The most significant finding of this study is the effect of exclusive breastfeeding being particularly important for the cognitive function of SGA children.

Conclusion

Most studies indicate the positive correlation between exclusive breastfeeding and cognitive development and IQ of infants later in life.  It is the goal of these studies to determine if the correlation is because of the actual human milk, or a result of the confounding factors inherently present.  Mothers who are more likely to breastfeed their infants exclusively for at least six months are usually educated, of a higher socioeconomic class, not of minority status and healthy themselves.  Another indication that breastfeeding has on infants is the amount of physical contact made with the infant when compared to bottle feeding.  Bottle fed babies are less likely to have the same amount of physical contact with their mothers.  Mother to infant eye contact is another factor involved that has yet to be studied exclusively.

It is difficult to rule out the above mentioned maternal factors in the study of the correlation between cognitive development and exclusive breastfeeding.  However, it is known that breastfeeding is the best and most effective form of nutrition for infants, especially those born small for gestational age.

There are some inconsistencies in the findings in terms of the overall impact on measurable cognitive function.  Longitudinal studies are inherently inconsistent at times because of the need for long term enrollment in the study itself.

A larger area of study would be consistent with the amount of fatty acid consumption and absorption in exclusively breastfed infants and those fed a mixture of infant formula and breastmilk.

Overall, the studies show that human milk for human babies is the best form of nutrition.  A link to intelligence is definitely made and is more than likely a combination of the chemical make-up of breastmilk, maternal factors and the inherent closeness and attachment that breastfeeding creates between mother and infant.

Molly Stepansky is a biologist turned SAHM mom to E (3 years) and N (8 months). She had to write a literature review for a class in graduate school, so she chose something near and dear to her heart.

References

1.     Slykerman, R., Thompson, J. M. D., Becroft, D. M. O., Robinson, E., Pryor, J., Clark, P., Wild, C. and Mitchell, E. (2005), Breastfeeding and intelligence of preschool children. Acta Paediatrica, 94: 832–837. doi: 10.1111/j.1651-2227.2005.tb01997

http://onlinelibrary.wiley.com/doi/10.1111/j.1651-2227.2005.tb01997.x/full

2.     Wieslaw Jedrychowski, Frederica Perera, Jeffry Jankowski, Maria Butscher, Elzbieta Mroz, Elizbieta Flak, Irena Kaim, Ilona Lisowska-Miszczyk, Anita Skarupa, Agata Sowa (2011

Effect of exclusive breastfeeding on the development of children’s cognitive function in the Krakow prospective birth cohort study), Eur J Pediatr DOI 10.1007/s00431-011-1507-5

http://www.ccceh.org/pdf-papers/Jedrychowski2011.pdf

3.     Quinn, P. J., O’Callaghan, M. J., Williams, G. M., Najman, J. M., Andersen, M. J. and Bor, W. (2001) The Effect Of Breastfeeding On Child Development At 5 Years: A Cohort Study. Journal of Paediatrics and Child Health, 37 5: 465-469.

http://espace.library.uq.edu.au/view/UQ:8593

4.     Avshalom Caspi, B Williams, J Kim-Cohen, I Craig, B Milne, R Poulton, L Schalkwyk, A Taylor, H Werts, T Moffitt. (2007)  Moderation of breastfeeding effects in the IQ by genetic variation in fatty acid metabolism.  PNAS November 20, 2007 vol. 104 no. 47 18860-18865

http://www.pnas.org/content/104/47/18860.short

5.      Geoff Der, G David Batty, Ian Deary (2006) The Effect of Breastfeeding on intelligence in children: prospective study, sibling pairs analysis and meta-analysis.  BMJ 333 : 945 doi: 10.1136/bmj.38978.699583.55 (Published 4 October 2006)

http://www.bmj.com/content/333/7575/945.short

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