© 2001 The Royal College of Psychiatrists
Correspondence |
Breast-feeding and schizophrenia
Department of Psychiatry, City General Hospital, Stoke-on-Trent, Staffordshire ST4 6QG
We read with interest the article by Leask et al (2000). They conclude against any protective association of breast-feeding with development of adult psychosis.
The authors have used two UK national cohorts. In the 1958 cohort, data were last collected when the members were 33 years old, therefore missing out a significant number of possible cases, which could have given more power and would have thus reduced the possibility of type 2 error in this study with so few cases. In only 29 of 40 cases of ‘narrow schizophrenia’ were data on breast-feeding available, which means a loss of 27.5%. These are the very cases who could have missed breast-feeding totally. We are also very curious as to why the narrow definition was used when the point of interest is relevant to the whole spectrum of schizophrenic disorder (especially after using "adult psychosis" in the title of their paper). Although the selection bias is largely taken care of by the nested design of the study, there is scope for recall bias, as breast-feeding interviews took place as long as 7 years after birth in one and after two years in the other cohort.
The original study (McCreadie et al, 1997), which the current study claims to refute, has a very strong logical appeal as it fits in nicely with the neurodevelopmental theory of schizophrenia implying diet, and therefore environment, and gene interaction. Again, this study also had a small sample of patients with data available only in 31% of cases (45/146). Of these cases, 77% were born between 1920 and 1960. However, the mothers were asked about the duration of breast-feeding with an expected precision of 1-2 weeks in 1989 only, again inviting recall bias. The other finding, which is difficult to explain away, is the fact that the siblings of these cases had a statistically similar pattern of breast-feeding, yet they did not develop schizophrenia.
In effect none of the studies can convincingly suggest any positive or negative association between breast-feeding and schizophrenia. This is doubly unfortunate as the clinical question asked has huge conceptual face validity and public health implications along with a very sensitive link with the neurodevelopmental understanding of schizophrenia.
REFERENCES
- Leask, S. J., Done, D. J., Crow, T. J., et al
(2000) No association between breast-feeding and adult
psychosis in two national birth cohorts. British Journal of
Psychiatry, 177,
218-221.
[Abstract/Free Full Text] - McCreadie, R. G. (1997) The Nithsdale
Schizophrenia Surveys 16. Breast-feeding and schizophrenia: preliminary
results and hypotheses. British Journal of Psychiatry,
170,
334-337.
[Abstract/Free Full Text]
Authors' reply
School of Community Health Sciences, University of Nottingham, Psychiatry & Community Mental Health, Duncan Macmillan House, Porchester Road, Nottingham NG3 6AA
Division of Psychology, University of Hertfordshire, Hatfield
POWIC, University Department of Psychiatry, Warneford Hospital, Oxford
MRC National Survey of Health and Development, University College London Medical School, London
Department of Psychiatry, University of Cambridge, Addenbrooke's Hospital, Cambridge
Mukherjee & Galanis express enthusiasm for the hypothesis that breast-feeding protects the infant against later schizophrenia. This despite widely published evidence, referenced at the beginning of our article, for a lack of any substantial relationship between breast-feeding and cognitive, emotional and social development in children (i.e. a lack of predictive validity of abnormal central nervous system development).
We examined the hypothesis in two cohorts (the 1946 National Survey of Health and Development (n=4447) and the 1958 National Child Development study (n=18 856)) in which the possibility of recall bias does not arise because, in contrast with the earlier report, the data were prospectively collected with respect to outcome. We observe no evidence that an individual's breast-feeding experience is significantly related to her/his later risk of schizophrenia.
May we suggest to those who wish to persuade us that the hypothesis is still viable that there is an onus to present findings from a larger and better-documented population.
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