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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

Dear Dr. Gupta,
Thank you for your questions, here are our answers:

1. There are many confounding factors with regard to the association of fish, n-3PUFA and breast cancer. As few of our included studies have adjustment for vitamin D consumption or exposure to sun-light, we could not adjust these confounding factors in our study. However, we have tried our best to achieve subgroup and meta-regression to examine the influence of other potential confounders, such as menopausal status, age, body mass index, dietary total energy intake and education level. We found that with or without adjustment of body mass index influenced the results (1).
2. It is true that a very small portion of dietary PUFA may be converted into trans-fats under some particular conditions, yet it is not the case in our study. The results of tissue n-3PUFA were highly consistent with that of dietary n-3PUFA. This indicated that the small amount converted to trans-fat could not influence the beneficial effect of dietary n-3PUFA on overall risk.
3. We have compared the association of n-3PUFA with breast cancer risk in different regions, such as Asian, Europe and U.S. Our subgroup analysis suggested that the inverse association of marine n-3PUFA with breast cancer risk was more evident in Asian countries than western countries. This may be because of the higher fish intake in Asian populations, such as Japanese, than western populations.

References:
1. 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. Zheng JS, Hu XJ, Zhao YM, Yang J, Li D. BMJ 2013;346:f3706.

Competing interests: No competing interests

04 August 2013
Ju-Sheng Zheng
Nutritionist
Duo Li
Department of Food Science and Nutrition, Zhejiang University
866 Yu-hang-tang Rd, Hangzhou, China