A report in the last 2011 issue of Psychotherapy and Psychosomatics introduces a new positive effect of breastfeeding.

Hostility is a personality construct that represents the opposite of warm attachment and that is closely related to a wide range of social and health problems, including mental health outcomes. Although the importance of cold and unsupportive parenting for the development of hostility has been recognized, there have been no studies focusing on the significance of breastfeeding on offspring hostility. The Authors of this report hypothesize that breastfeeding protects the child from developing a hostile personality in adulthood. The study was conducted on a population-based sample of the Young Finns Study consists of Finnish children and adolescents randomly selected to represent the whole of Finland. The eligible sample consisted of 1,917 participants born full term with birth weights 6 2,500 g and whose hostility was measured in 1992, 1997, 2001 and 2007. Altogether 5,501 participant observations were available from the 4 study waves.

Breastfeeding was measured in 1983 when the children were on average 12.6 years of age. The parents were asked to report the child’s breastfeeding history and additionally to check the information from personal record cards that are obtained by all Finnish mothers. Hostility was assessed with 3 scales at 4 time points in 1992, 1997, 2001 and 2007, when participants had a mean age of 21.5, 26.7, 30.8 and 36.9 years, respectively. ‘Cynicism’ was measured with a scale derived from the Minnesota Multiphasic Personality Inventory, ‘paranoia’ with a subscale of the Symptom Checklist-90R, and ‘anger’ with the irritability scale of the Buss-Durkee Hostility Inventory. A total hostility score was calculated as a mean of the cynicism, paranoia and anger subscales. Most of the mothers had breastfed their child (88.2%), and the average duration of breastfeeding was 4 months. On average, mothers were 27 years old at childbirth, and most of the children were born to nuclear families with 2 - 3 children. The offspring were mostly women (54.5%) with a mean age of 29 years.

The offspring had an average hostility score of 2.53 in adulthood, with cynicism (2.86 vs. 2.68) and paranoia (2.36 vs. 2.29) higher among men, and anger higher among women (2.38 vs. 2.62). Older mothers were less likely than younger mothers to breastfeed (mothers’ average age at delivery 29.6 vs. 27.0 years among not breastfed vs. breastfed) but the duration of breastfeeding increased with mother’s age Longer duration of breastfeeding was related to less hostile maternal child-rearing practices (r = - 0.10), lower family income (r = - 0.06), higher number of children in the family (r = 0.11) and later birth order of the child (r = 0.14). Of these family characteristics, hostile child-rearing (r = 0.13) and low family income (r = - 0.10) correlated with higher offspring hostility in adulthood (all ps’<0.001). In age- and sex-adjusted multilevel regression models, breastfeeding status predicted total hostility, cynicism and paranoia but not anger. Those who had not been breastfed as infants had higher levels of hostility, especially cynicism and paranoia, in adulthood than their 4- to 6-month-breastfed peers. This population-based study showed that breastfeeding may have long-term effects on offspring hostility. Those who were not breastfed in infancy had higher levels of adult hostility than those who were breastfed.

The association was U-shaped showing that psychological benefits of breastfeeding may already be acquired during the first 6 months, thus even short breastfeeding should be encouraged in maternity clinics. However, long-term breastfeeding of more than a year was not related to lower hostility, which may be explained by other family characteristics associated with longer breastfeeding duration and hostility. This study has the following limitations. First, self-reports of breastfeeding might inflict bias due to recall or social desirability problems. Second, the most disadvantaged participants had dropped out from the study. Future studies should examine potential mechanisms explaining the association between breastfeeding and personality outcomes.

Full bibliographic information: Merjonen, P. ; Jokela, M. ; Pulkki-Råback, L. ; Hintsanen, M. ; Raitakari, O.T. ; Viikari, J. ; Keltikangas-Järvinen, L. Breastfeeding and Offspring Hostility in Adulthood. Psychother Psychosom 2011;80:371-373