A Critical Evaluation into the Relationship between Breastfeeding and Adult Intelligence: A literature review
Introduction
Breastfeeding has revealed short-term health benefits including the prevention of infectious diseases and allergies, as well as long term benefits such as healthier immune system responses (NHS Choices, 2017). According to research, babies that are breast fed are more likely to have better brain and cognitive development compared to babies that are bottle-fed (Gale & Martyn, 1996). There is also evidence to suggest that there are associations between breastfeeding and adult intelligence, specifically in areas such as educational attainment and cognitive functions.
The aim of this literature review is to critically evaluate papers that describe the relationship between breastfeeding and adult intelligence across three spectrums, which include educational attainment, cognitive functions and abilities. This paper will specifically evaluate confounding variables such as maternal education as well as investigate the effects of breastfeeding on verbal memory and fluency, mental speed and concentration (Richards et al., 2002). The structure of this literature review is based on a paper written by Callen and Pinelli (2004). A thorough search strategy has shown that there are limited numbers of papers published after 2000 around breastfeeding and adult intelligence. Therefore, most papers included in this review are from the year 2000 and before this date.
Search Strategy
Searches for this literature review were conducted in databases including Web of Science, PSYCHinfo and Medline. The initial search hit resulted in thirty-one articles in Medline, ten articles in PSYCHinfo, and twenty-eight articles in Web of Science. This literature review includes nine articles and the searches were limited by the term “adult intelligence”; they were not limited to being psychology-related articles only. Additionally, searches were filtered to keywords and title only in each database. The literature search involved using the key terms, ‘’breastfeeding’’ combined with “adult intelligence’, using the link word “and”. Additional studies out-with the search criteria included trends in Asia that focuses on the effects of socioeconomic status on breastfeeding (Chua et al., 1989) as well as the relationship between dummy use, breastfeeding and intelligence (Gale & Martyn, 1996).
Methodology and Discussion
There is evidence to suggest that good educational attainment is correlated to breast-feeding. Gale and Martyn’s paper (1996), which was based in the UK, investigated the association between breastfeeding, dummy use and adult intelligence through domains including social class and the environment. Within the study, two datasets were collected of which the first consisted of 298 participants that agreed to do a psychometric test and 696 participants in the second set agreed to do the same. In order to analyse the data, multiple linear regression was used to investigate the correlation between feeding methods and the score in IQ tests. According to the paper, participants whose mothers were aged 35 years or older at the time of their birth scored 5.8 points higher in IQ (intelligence quotient) tests than those whose mothers were aged under 20 years (Gale & Martyn, 1996). This illustrates that mature mothers were more likely to have higher qualifications, better work experience and independence compared to younger mothers.
However, the confounding variables in Gale and Martyn’s (1996) paper such as measures of socioeconomic status and intelligence need to be taken into account when analysing data. In order to reduce these confounds, future studies should introduce control variables, which allows for more standardised and valid results. This is due to underlying assumptions being associated with older mothers and intelligence. Furthermore, confounding variables such as the type of environment which the mother provides for their child and child-rearing should be considered when analysing data (Gale & Martyn, 1996). A limitation of the study is that controls should be set up for the child’s social environment in which they are breastfed or bottle-fed. This can determine whether the environment is a factor to consider in correlation to the child’s cognitive abilities and intelligence.
A similar recent study explored the relationship between educational attainment and breastfeeding in Brazil (Victora et al., 2015.) Within the birth cohort study, there were a total of 5914 participants of which 3493 participants were involved in a WAIS test (Wechsler Adult Intelligence Scale) that measures verbal comprehension and working memory. The key findings of the paper revealed that confounds included maternal age and pregnancy as well as the effects of smoking on pregnancy. However, comparative studies can be created to investigate factors such as the effects of alcohol and drugs on pregnancy, breastfeeding and consequently intelligence. Additionally, how does socioeconomic status contribute towards the attitudes of mothers and whether they choose to breastfeed or not? Cooper’s paper (2015) suggests that the variable of genetics in connection to intelligence was not considered within Victora et al. (2015) paper.
Moreover, a paper exploring breastfeeding trends in Singapore revealed that additional factors such as cultural differences and traditional practises influenced a mother’s decision to breastfeed or bottle-feed (Chur et al., 1989). The authors state that the differences in economic groups were due to increased affluence and education. However, this study is limited in comparisons between various ethnic groups across continents, for example Asia and South America. This comparison would illustrate any significant differences amongst ethnic groups in terms of beliefs and attitudes towards breastfeeding. Additionally, how far do beliefs and traditional practises influence attitudes of mothers?
Furthermore, Richards, Hardy and Wadsworth’s paper (2002), which was based in the UK, illustrates how breastfeeding has an impact on reading ability, verbal memory, attention and concentration. The NART (National Adult Reading Test) was used to measure verbal memory, mental speed and concentration and logistic regression analysis was used to analyse the variables (Richards, Hardy & Wadsworth, 2002). The results from the study indicate there was no association between breastfeeding and verbal memory or reading ability. The confounding variables within this study included gender and family background, however, this study did not consider whether there were differences between breast-feeding and bottle-feeding on cognitive decline.
A similar study, which was based in Denmark, investigated the association between the duration of breastfeeding and adult intelligence using two datasets, which consisted of 973 participants and 2280 participants (Mortensen et al., 2002). Although the results indicate that breastfeeding is positively correlated with the likelihood of obtaining advanced educational qualifications, the study does not consider comparisons to bottle-feeding. It also fails to investigate attachment styles in relation to the mother and child. Furthermore, does parental behaviour predict breastfeeding outcomes?
Although the majority of studies have focused on the association between adult intelligence and breastfeeding, a recent study investigated the effects of breastfeeding and cognitive abilities in older men. According to the article, 931 men from Helsinki completed the Finnish equivalent to a WAIS test. The results show that men who were breastfed had better cognitive abilities in young adulthood than those who were never breastfed, and this advantage was present in old age as well (Rantalainen et al., 2017). Some of the limitations of the study included high attrition rates and selection bias as the sample of men were from Helsinki only. Future studies should investigate the impact of culture on breastfeeding amongst various areas within Finland.
Overall, the similarities between the studies are that maternal education and social class appear to be the two key factors, which influence breastfeeding attitudes and consequently a child’s intelligence. However, factors such as beliefs and attitudes in Asia differ to those in Brazil, the UK and Denmark thus future studies should investigate the role that culture plays in breastfeeding attitudes. The above evidence shows that breast-feeding and intelligence are correlated to a range of factors, specifically socioeconomic status. Future studies should focus on the impact of attachment styles and mother’s attitudes to breastfeed or bottle-feed. The above studies also fail to consider how influential siblings or twin studies would be in terms of genetics and its association to intelligence; thus, future studies should explore this.
Written by Evelyn Antony
“Hello! My name is Evelyn and I recently graduated from the University of Edinburgh with a Master of Arts (with Honours) degree in Psychology. My undergraduate dissertation leveraged data from the UK Millennium Cohort Study, where I investigated the role of emotional dysregulation in explaining the association between ADHD and internalising emotional problems amongst young children. Throughout my degree, I have acquired valuable and meaningful experiences working with young people that have profound mental health issues and additional needs, as well as working in research and events management within higher education settings. Collectively my work experiences and undergraduate degree in psychology has led me to pursue postgraduate studies, in educational psychology, which commences later in 2021.”
Connect with Evelyn on Linkedin and through her personal blog.
References
Benefits of breastfeeding - Pregnancy and baby guide - NHS Choices. (2017). Nhs.uk. Retrieved: 05/11/2020. http://www.nhs.uk/Conditions/pregnancy-and-baby/Pages/benefits-breastfeeding.aspx
Callen, J., & Pinelli, J. (2004). Incidence and Duration of Breastfeeding for Term Infants in Canada, United States, Europe, and Australia: A Literature Review. Birth, 31(4), 285-292. http://dx.doi.org/10.1111/j.0730-7659.2004.00321.x
Chua, S., Viegas, O., Counsilman, J., & Ratnam, S. (1989). Breastfeeding trends in Singapore. Social Science & Medicine, 28(3), 271-274. http://dx.doi.org/10.1016/0277-9536(89)90270-0
Cooper, C. (2015). Breastfeeding and adult intelligence. The Lancet Global Health, 3(9), 519. http://dx.doi.org/10.1016/s2214-109x(15)00062-5
Gale,C., & Martyn, C. (1996). Breastfeeding, dummy use and adult intelligence. The Lancet, 347 (9008), 1072-1075. http://dx.doi.org/10.1016/s0140-6376(96)90278-0
Mortensen, E., Michaelsen, K., Sanders, S., & Reinisch, J. (2002). The Association Between Duration of Breastfeeding and Adult Intelligence. Obstetrical & Gynecological Survey, 57(10), 659-661. http://dx.doi.org/10.1097/00006254-200210000-00009
Rantalainen, V., Lahti, J., Henriksson, M., Kajantie, E., Mikkonen, M., Eriksson, J., & Raikkonen, K. (2017). Association between breastfeeding and better preserved cognitive ability in an elderly cohort of Finnish men. Psychological Medicine, 1-13. http://dx.doi.org/10.1017/s0033291717002331
Richards, M., Hardy, R., & Wadsworth, M. (2002). Long-term effects of breast-feeding in a national birth cohort: educational attainment and midlife cognitive function. Public Health Nutrition, 5(5), 631-635. http://dx.doi.org/10.1079/phn2002338
Victora,C., Horta B., de Mola, C., Quevedo, L., Pinheiro, R., Gigante,D., Goncalves, H., & Barros, F. (2015). Association between breastfeeding and intelligence, educational attainment, and income at 30 years of age: a prospective birth cohort study from Brazil. The Lancet Global Health, 3 (4), e199-e205. http://dx.doi.org/10,1016/s12214-109x(15)70002-1