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Gender differences in the effect of breastfeeding on adult psychological well-being

Noriko Cable , Mel Bartley , Anne McMunn , Yvonne Kelly
DOI: http://dx.doi.org/10.1093/eurpub/ckr135 653-658 First published online: 22 October 2011

Abstract

Background: Little is known about whether the positive effect of breastfeeding on child health extends to adult psychological adjustment. We hypothesized that breastfed babies would have higher psychological well-being in adulthood in relation to the pathway of childhood psychosocial adjustment. Methods: We used the available cases with normal birthweight from the National Child Development Study (NCDS, N = 7304, born in 1958) and the 1970 British Cohort Study (BCS70, N = 6205, born in 1970). Childhood psychosocial adjustment was assessed by the child's teacher, using the Bristol Social Adjustment Guides for the NCDS and the Rutter Behaviour Scale for the BCS70. Adult psychological well-being was defined in terms of measures of emotional distress and self-efficacy. In this study, we controlled the effects of socio-demographic factors at birth: maternal age and educational status, two-parenthood and being a first-born child. We used path analysis to test life-course pathways between breastfeeding and adult psychological well-being independent of socio-demographic factors at birth and the role childhood psychosocial adjustment. Results: After accounting for the effects of the socio-demographic factors at birth, being breastfed indirectly contributed to adult psychological well-being among women through the pathway from childhood psychosocial adjustment. Moreover, this was directly associated with better psychological well-being in adulthood among women from the BCS70. Being breastfed was not associated with psychological outcomes amongst men in either cohort. Conclusions: Being breastfed contributed to psychological outcomes in women, especially from the later born cohort. Our findings suggest that being breastfed can be important for women's psychological well-being throughout the lifecourse.

Introduction

The British government is now committed to supporting exclusive breastfeeding for at least 6 months of the birth of the child because of rich nutritional values of breast milk.1 Breastfeeding protects young children from childhood infection2 and obesity3,4 and aids their cognitive development.5 These positive effects attributed to breastfeeding have been found to be carried over to adulthood. Adults who were breastfed at birth experienced better cardiovascular health,6 lower blood pressure, cholesterol and weight7 than those who were not. Moreover, the cognitive benefits of breastfeeding have been reported in a British birth cohort born in 1946 at age 26 years and up to age 53 years.8

It is also claimed that breastfeeding offers psychological benefits by encouraging attachment with the mother, including in children adopted at an early age;9 however, the positive effect appears not to be limited to very early age. Breastfeeding was found to promote better psychosocial adjustment among young children and adolescents in Australia,10 including young children experiencing parental separation in Great Britain.11 Extensive breastfeeding was not shown to have any significant protective effects on conduct disorders or mental health problems among adolescents in New Zealand,12 whereas the previously mentioned Australian study showed that extensive breastfeeding for 6 months or longer contributed to children's better overall psychosocial adjustment including both internalized and externalized problems.10 Findings linking breastfeeding and psychological health in adulthood are inconclusive.

These inconclusive findings may be due to differences in outcome measures between studies. Although it was reported that there was no significant association between breastfeeding and adult schizophrenia among British birth cohorts born in 1946 and 1958,13 any positive effects of breastfeeding on psychological outcomes in childhood or adulthood may be better reflected in terms of psychosocial adjustment or emotional stability, rather than in the incidence of a particular mental illness.

The life-course approach can provide information on the very little known area of a longitudinal pathway between breastfeeding and adult psychological well-being. The life-course approach allows for the possibility that factors in the aetiological pathway may act both directly on the outcome and indirectly via mediating variables.14,15 Research has documented a link between childhood and adult psychological health.16,17 Taking the life-course approach, we are able to test the ways in which breastfeeding may contribute to psychosocial adjustment in childhood, and promote adult psychological well-being in this way.

Here, we also allow for the known differences in psychological development between men and women. Poor psychosocial adjustment, such as conduct disorder, in childhood is more common in boys,18 whereas in adulthood women are found to have a higher risk of anxiety or depression or both.19,20 Pathways through the life-course from breastfeeding and infant attachment to adult psychological well-being therefore can differ. In women, it is more likely that the effect of breastfeeding on adult psychological well-being may act through both direct and indirect pathways. A positive effect of breastfeeding in the form of secure attachment may become more relevant to forming relationships in later life. In addition, better behavioural adjustment in childhood may set girls onto a generally more favourable pathway into adult life.

The aim of this study is to examine the role of breastfeeding on childhood psychosocial adjustment and adulthood psychological well-being, using two British Birth Cohort Studies born 12 years apart. We hypothesize that breastfeeding may play a different role for psychological health across lifecourse between men and women. We anticipate observing an indirect effect of breastfeeding on adult psychological well-being through the pathway from childhood psychosocial adjustment for men. On the other hand, the effect of breastfeeding on women's psychological well-being is hypothesized to be both direct and indirect through the pathway of childhood psychosocial adjustment.

Methods

Data

We used the available cases from the National Child Development Study (NCDS, N = 7304) and the 1970 British Cohort Study (BCS70, N = 6205) who were born with normal birthweight (≥ 2500 g or equivalent) to minimize the bias from breastfeeding practice due to prematurity. For childhood data, we used data sets obtained from birth, age 7 and 11 years of the NCDS21 and birth,22 523 and 10 years24 of the BCS70. For adulthood data, we used data sets obtained from age 33 years for the NCDS25 and age 30 years for the BCS70.26 Purposes and the design for the NCDS27 and the BCS7028 have been described elsewhere. These are public domain data, freely accessible via UK Data Archive for academic purposes. Principle investigators responsible to each birth cohort study obtained ethical approval for the data collection. Use of these public domain data requires no contact with cohort members, and data are meticulously anonymized.

Measures

Breastfeeding

Information about breastfeeding practice was asked of the mother when the child was age 7 years for the NCDS and age 5 years for the BCS70. If a mother breastfed her child for ≥1 month, this variable was coded as one. If the duration of breastfeeding was < month, it was coded as zero. The upper limit of the response category for the breastfeeding practice obtained from the mothers of the NCDS children was ≥1 month. This crude measure was taken to make results comparable between two data sets.

Childhood psychosocial adjustment

Childhood psychosocial adjustment was assessed using a total score obtained from the Bristol Social Adjustment Guides for the NCDS at age 11 years and selected questions from the Rutter Child Behaviour Scale29 for the BCS70 at age 10 years. These scales, both graded by a teacher, were extensively used in both cohort studies to show each child's psychosocial adjustment. These two scales were valid indicators of children's psychosocial adjustment and fairly comparable, as a total score.30 Square-root transformed scores were used to achieve a normal distribution in each scale, treating them as continuous measures. A high score in both scales indicates poor psychosocial adjustment.

Adult psychological well-being

Psychological well-being was indicated by two measures: emotional distress, based on the score obtained from the Malaise Inventory and self-efficacy. A 24-item Malaise Inventory29 was administered when the NCDS cohort members were at 33 years of age and the BCS70 cohort members were at 30 years of age. As suggested by Rogers et al.,31 a cut-off point of ≥7 is applied to indicate the state of emotional distress.

Self-efficacy was derived from three items asking cohort members about self-perceived control over their life when cohort were aged 33 years for the NCDS and 30 years for the BCS70. The same three efficacy questions were asked in the two cohorts. The score on the self-efficacy items ranged 0 to 3, with 3 representing the greatest self-efficacy. The majority of the study participants fell into the highest end of the score. Therefore, the code of one was used for those who replied ‘yes’ to all three items and zero for the rest.

Socio-demographic factors at birth

Breastfeeding is reported to be associated with mother's higher level of education, partnership and parity in Great Britain.32 Age was also associated with breastfeeding in New Zealand.33 Adjusting for the effects of those socio-demographic factors at birth is necessary to show the presence of an independent effect of breastfeeding on the child and adult psychological outcomes.

Dichotomized variables were created for whether children were born into a two-parent household, whether the cohort member's mother was ≥20-years old at the birth of the study child, whether the mother had left full-time education at the minimum leaving age, and whether the cohort member was the first born child. This was obtained from the birth data for both cohorts. Presence of each condition was coded one with absence being zero. These crude measures were taken to make results comparable between two data sets.

Statistical analysis

Descriptive characteristics of the participants were assessed, using Stata v11.0.34 We conducted path analysis to examine direct pathways between breastfeeding and adult psychological well-being as well as indirect pathways via childhood psychosocial adjustment over and above the effects of socio-demographic factors at birth, using Mplus v5.0.35

Results

Descriptive findings

Most members of both cohorts were breastfed for <1 month or not breastfed at all. Breastfeeding for >1 month decreased between 1958 and 1970. Nearly a half of mothers of the NCDS cohort members reported that they breastfed their child for ≥1 month, whereas only ∼20% of mothers of BCS70 cohort members did so. There were no apparent differences in breastfeeding practice in either cohort according to the sex of the child.

In NCDS, about 42% of mothers, who left their full-time education at the minimum leaving age, breastfed their baby ≥1 month, whereas around 55% of mothers who stayed in their full-time education beyond the minimum leaving age breastfed their baby ≥1 month. Only 20–26% of children of lone mothers were breastfed compared with 46% of children in two-parent households. In BCS70, more mothers with higher education (∼30%), a partner (∼20%) and aged ≥20 years (∼20%) breastfed their baby for ≥1 month compared with those who were not. In both cohort studies, there were few cases of teenage motherhood or lone parenthood (table 1).

View this table:
Table 1

Proportions (%) of breastfeeding 1 month or longer by socio-demographic factors at birth presented by cohorts and gender

BoysGirls
NCDS (N = 3628)BCS70 (N = 3034)NCDS (N = 3676)BCS70 (N = 3171)
Percentage of breastfeeding  + 1 month out of the row total (n)Percentage of breastfeeding  + 1 month out of the row total (n)Percentage of breastfeeding  + 1 month out of the row total (n)Percentage of breastfeeding  + 1 month out of the row total (n)
Mother stayed full time education until minimum leaving age
    No41.55 (2676)14.90 (1953)42.31 (2699)17.33 (2043)
    Yes54.73 (952)31.64 (1081)55.78 (977)35.37 (1128)
Two parent household
    No20.00 (75)17.74 (62)25.84 (89)11.36 (88)
    Yes45.54 (3553)20.93 (2972)46.39 (3587)24.10 (3083)
Mother's age over 20
    No46.63 (163)14.77 (237)40.33 (181)17.52 (234)
    Yes44.94 (3465)21.38 (2797)46.18 (3495)24.24 (2937)
First born child
    No43.12 (2312)20.32 (1890)44.57 (2302)22.50 (1929)
    Yes48.33 (1316)21.77 (1144)48.11 (1374)25.68 (1242)

Descriptively boys from both cohorts had higher mean values on the childhood psychosocial measure (mal-adjusted) than girls. In addition, the group who were breastfed >1 month had lower mean values on the psychosocial adjustment measure (well-adjusted) in both cohorts compared to those who were not breastfed ≥1 month (table 2). In adulthood, the majority of men and women from both cohorts reported low levels of emotional distress and high self-efficacy. Similar to what was found in childhood psychosocial adjustment, more adults from the group who had been breastfed ≥1 month showed absence of emotional distress and higher self-efficacy. The proportion reporting being emotionally distressed was highest in women from the BCS70; however, women in this cohort also had the highest proportion with high level of self-efficacy.

View this table:
Table 2

Descriptive information for child psychosocial adjustment and adult psychological well-being by breastfeeding, presented by cohort and gender

CohortBreast feedingChild psychosocial adjustmentAdult psychological well-being
Meana (95% CI)No emotional distress (%)High self-efficacy (%)
Male
    NCDS (N = 3628)<1month (n = 1995)2.54 (2.47–2.61)94.5469.72
+1month (n = 1633)2.47 (2.40–2.55)94.7372.75
    BCS70 (N = 3034)<1month (n = 2401)12.70 (12.57–12.83)85.9273.34
+1month (n = 633)12.49 (12.23–12.76)87.3676.15
Female
    NCDS (N = 3676)<1month (n = 1989)2.09 (2.03–2.16)88.0872.55
+1month (n = 1687)1.93 (1.87–2.00)90.2875.58
    BCS70 (N = 3171)<1month (n = 2418)12.30 (12.17–12.43)80.0276.43
+1month (n = 753)11.81 (11.59–12.03)85.3982.47
  • a: Based on square root transformed values. Higher values indicate ‘mal-adjustment’

Findings of path analysis

Path analysis showed gender and cohort differences in pathways from breastfeeding to adult psychological well-being via childhood psychosocial adjustment. Apart from maternal age, all socio-demographic factors at birth contributed directly to breastfeeding in the NCDS cohort who were born in 1958 (see Supplementary Data). The effect of living in a two-parent household was the largest followed by the effect of maternal education. In the BCS70, maternal education showed a strong direct effect on breastfeeding. Living in a two-parent household provided an additional effect to breastfeeding among girls in this cohort. Being a first born was significantly associated with being breastfed for one month or more in the NCDS cohort; however, this was not significant in the cohort born in 1970 (BCS70).

The effect of breastfeeding on childhood psychosocial adjustment was almost non-existent for boys in both cohorts, failing to support a significant direct effect of breastfeeding on childhood psychosocial adjustment. In contrast, there was a significant direct effect of breastfeeding on childhood psychosocial adjustment in girls from both cohorts, which was independent of mother's age and education, family structure and presence of older siblings. The effect of breastfeeding on childhood psychosocial adjustment was stronger in girls and in the later born cohort (table 3).

View this table:
Table 3

Path coefficients for the pathways from independent variables to outcomes, presented by cohort and gender

NCDSBCS70
Childhooda psychosocial adjustmentAdult emotional distressAdult self-efficacyChildhooda psychosocial adjustmentAdult emotional distressAdult self-efficacy
Men(N = 3628)(N = 3034)
    Breastfeeding−0.0070.0080.032−0.025−0.0100.019
    Maternal education−0.327***−0.1640.168**−0.633***−0.1090.123*
    Maternal age−0.396**−0.2180.352**−0.342−0.434***0.340***
    Two-parent household−0.614**0.0120.233−0.6210.1350.215
    Being the first born−0.278***−0.252**0.147**0.115−0.162**0.160**
    Childhood psychosocial adjustmenta0.095***−0.113***0.055***−0.045***
Women(N = 3676)(N = 3171)
    Breastfeeding−0.061*−0.0430.030−0.203*−0.090*0.078*
    Maternal education0.444***−0.200**0.101−0.451***−0.0360.148**
    Maternal age−0.281**−0.177−0.007−0.546*−0.211*0.076
    Two-parent household−0.411**−0.0230.176−0.754*−0.0270.325*
    Being the first born−0.121*−0.135*0.247***−0.182−0.0710.133*
    Childhood psychosocial adjustmenta0.132***−0.139***0.056***−0.048***
  • *P < 0.05; **P < 0.001; ***P < 0.0001

  • a: Higher values of childhood psychosocial adjustment indicate ‘mal-adjustment’

When the direct effects of breastfeeding on adult psychological well-being were tested, breastfeeding was significantly associated with better adult psychological well-being in women in BCS70, indicated by emotional distress and self-efficacy, over and above socio-demographic factors at birth and childhood psychosocial adjustment (table 3). In the NCDS women, the effects of breastfeeding, adjusted for all social demographic factors at birth and childhood psychosocial adjustment, were not significant for either adult emotional distress or self-efficacy, failing to support a significant direct effect on adult psychological well-being. Similarly to what we found for the relationships between breastfeeding and childhood psychosocial adjustment, breastfeeding did not show any significant independent effects on adult psychological well-being among men from either cohort.

An indirect pathway from breastfeeding to adult psychological well-being, via childhood psychosocial adjustment was significant in women from both cohorts, supporting our hypothesis of an indirect effect of breastfeeding on adult psychological well-being via childhood psychosocial adjustment (table 4). In women from the later born cohort (BCS70), those effects were appeared to be slightly larger than the effects found in women from the 1958 cohort (NCDS).

View this table:
Table 4

Direct, indirect, and total effects for the pathways from breastfeeding to adult psychological well-being via childhood psychosocial adjustment, presented by cohorts and gender

NCDSBCS70
DirectIndirectTotalDirectIndirectTotal
Men
    Breastfeeding to emotional distress0.008−0.0010.007−0.010−0.001−0.012
    Breastfeeding to self efficacy0.0330.0010.0010.0190.0010.020
Women
    Breastfeeding to emotional distress−0.043−0.008*−0.051−0.090*−0.011*−0.101**
    Breastfeeding to self efficacy0.0300.008*0.0390.078*0.010*0.088*
  • Note: All effects were accounted for the effects of socio-demographic factors at birth

  • *P < 0.05; **P < 0.001, ***P < 0.0001

In sum, breastfeeding contributed indirectly to adult psychological well-being via the pathway from childhood psychosocial adjustment in women. In the later born cohort (BCS70) of women, breastfeeding also showed a direct effect on adult psychological well-being. We did not find any significant associations between breastfeeding and child or adult outcomes for men in either cohort.

Discussion

Main findings

We found an indirect effect of breastfeeding on adult psychological well-being via the pathway from childhood psychosocial adjustment in women from both cohorts. For women from the BCS70 cohort, breastfeeding directly contributed to adult psychological well-being which partially supports our hypothesis. In this study, we adjusted for maternal education and age, being born in a two-parent household, and being a first born in the model; all significant effect of breastfeeding on childhood psychosocial adjustment and adult psychological well-being is therefore independent of those effects.

Men did not gain significantly measured psychological benefit, in either childhood or adulthood, from being breastfed for longer than one month, failing to fully support our hypothesis. The absence of significant associations between breastfeeding and childhood or adulthood psychological outcomes in men was not anticipated. It has been reported that breastfeeding contributes to the quality of the parent–child relationship among adolescents.12 On the other hand, Kramer et al.36 did not support the claim of protective effects of breastfeeding on children's behaviour. Previous studies often did not account for possible gender differences in the pathway between breastfeeding and childhood outcomes. Our study is the first to show that a psychosocial benefit of breastfeeding in childhood may be specific to girls.

In our study, the protective effect of breastfeeding on childhood and adult outcomes among women born in 1970 was not replicated in adulthood among women born in 1958 which was not anticipated. Fewer mothers of the 1970 cohort children breastfed their child compared to the mothers of the cohort born in 1958.One could speculate that breastfeeding in 1970 could be a reflection of different motivation compared to mothers’ motivation to breastfeed in 1958. The social distribution of breastfeeding also changed: in the earlier cohort (NCDS) ∼55% of mothers who stayed in full-time education beyond the minimum leaving age breastfed for over 1 month compared to ∼42% of those who left at the minimum leaving age, whereas the comparable figures for the 1970 cohort were ∼30% and 16%. In the 1958 cohort, mothers <20 years of age were actually more likely to breastfeed (43%) as compared to ∼16% in the 1970 cohort.

It seems that as the prevalence of breastfeeding decreased, the practice came to represent different maternal characteristics in a way that perhaps is not captured by adjustment for the socio-demographic confounders available to us. There is no information about whether female cohort participants breastfed their own children or not which we would have liked to investigate. Our aim is to examine a longitudinal pathway from breastfeeding to adult psychological well-being via a childhood psychosocial pathway. We did not include other independent variables, which would not have been relevant to this pathway. We found an indirect pathway from breastfeeding to adult psychological well-being via childhood psychosocial adjustment in women from both cohort studies. The direct effect of breastfeeding on adult psychological well-being in BCS70 women, however, needs careful interpretation. Maternal psychological health at the birth of the cohort child could be a confounder for breastfeeding and psychological well-being of the cohort participants. We could not adjust for this, as the data were not available to us. Future studies that include more comprehensive information are needed to advance our understanding of the context of socio-demographic confounders for breastfeeding and psychological outcomes across time.

Previous studies have found a dose–response relationship of breastfeeding with motor milestones37 and lung function.38 In our study, we were unable to test for similar dose-response relationship of breastfeeding, from zero to up to 6 months, because the response category to indicate the duration of breastfeeding was limited to one month or more in the 1958 cohort (NCDS). Also, there was no information about the exclusiveness of breastfeeding practice at the time of the survey in both cohort studies. We therefore could not test whether the current recommendation of exclusive breastfeeding up to 6 months might be likely to lead to better psychosocial outcomes in childhood. Additionally, mothers of the cohort children were retrospectively asked about their breastfeeding practice (age 7 years for NCDS, age 5 years for BCS70). According to the Infant Feeding Survey in 1975, mothers in England and Wales were still breastfeeding when their children were 6-week old39; this figure is similar to the proportion obtained from the BCS70.

Breastfeeding has been increasing since 1970; 76% of mothers in the UK initiated breastfeeding in 2005.40 Kelly and Watt41 reported that 34% of the babies from the Millennium Cohort Study (MCS) were still breastfed at one month of age, whereas it was 23% for the mothers of the BCS70 children. Given this revival of breastfeeding practice, it will be possible to examine whether the effect of breastfeeding on mid-childhood psychosocial maladjustment and gender-specific associations between these factors extends to the children in the MCS.

Conclusions

We found that a significant effect of breastfeeding on childhood psychosocial adjustment, which indirectly contributed to adulthood psychological well-being in women. Moreover, we found a direct pathway, not mediated by childhood psychosocial adjustment, from breastfeeding to adult psychological well-being among women born in 1970. Although a significant direct path from breastfeeding to adult psychological well-being was not supported in the cohort of women born in 1958, their psychological well-being benefitted from having better psychosocial adjustment in childhood due to breastfeeding. Our findings suggest that breastfeeding can be important to women's psychological well-being across the life-course. Policies to support mothers with babies to breastfeed, especially to those who are socially disadvantaged will improve girl's psychosocial adjustment and ensure their psychological well-being across life-course.

Supplementary data

Supplementary data are available at EURPUB online.

Funding

This study was a project from the International Centre for Lifecourse Studies in Society and Health, supported by the Economic and Social Research Council (RES-596-28-0001).

Conflicts of Interests: None declared.

Key points

  • Although there is no apparent gender specific pattern in breastfeeding practice, breastfeeding appears to benefit girls’ psychosocial adjustment independent of social demographic factors at birth.

  • Being breastfed directly and indirectly contributed to adult psychological health and self-efficacy among women from the later born cohort.

  • Being breastfed can be an important driving factor for women's psychological well-being across lifecourse.

Acknowledgements

All data are supplied by the UK Data Archive and copy righted by the Centre for Longitudinal Studies, Institute of Education. The UK Data Archive bears no responsibility for further analysis or interpretation on the data used in this study. This study was presented at the 11th International Congress of Behavioral Medicine in Washington DC, USA, 4–7 August 2010, the Society for Social Medicine Conference in Belfast, UK, 4–7 September 2010 and the Society for Longitudinal Studies Conference in Cambridge, UK 22–24 September 2010.

References

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