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Intake of fish and marine n-3 polyunsaturated fatty acids and risk of breast cancer: meta-analysis of data from 21 independent prospective cohort studies

BMJ 2013; 346 doi: https://doi.org/10.1136/bmj.f3706 (Published 27 June 2013) Cite this as: BMJ 2013;346:f3706

Re: Intake of fish and marine n-3 polyunsaturated fatty acids and risk of breast cancer: meta-analysis of data from 21 independent prospective cohort studies

This paper relies on a disparate collection of studies from very different world regions, to establish that fish oil is a protective factor in the causation of breast cancer. It is a daunting challenge. To account for all the possible con-founders in such a widespread population, even with access to the raw data is, seems impossible.

Diet, UV light exposure, intake of female hormones as replacement therapy or as the contraceptive pill, and the thorny question of level of screening all add to the problem of attribution of any beneficial or detrimental effect to any single cause - in this case fish oils. The big data on the prevalence of breast cancer based on Seers data and population trends for the past 50 years suggest correlation of increasing incidence with 1. declining birth rate 2. use of hormonal contraception. 3. skewing towards developed countries where these patterns of behavior have been endemic for roughly that duration of time, and not on any particular dietary component. It would also be expected that other cancers would respond similarly to fish oil if it is a true effect, but the data concerning other cancers are unconvincing.

The findings of this study are impressive and need replication with raw data without the presence of con-founders to make any definite correlations.

Competing interests: No competing interests

22 July 2013
Mike K Thomson
Scientist
St Georges London
St Georges UK