HEALTH NEWS

Study Title:

Fish Oil and Breast Cancer Risk

Study Abstract

Objectives To investigate the association between intake of fish and n-3 polyunsaturated fatty acids (n-3 PUFA) and the risk of breast cancer and to evaluate the potential dose-response relation.

Design Meta-analysis and systematic review of prospective cohort studies.

Data sources PubMed and Embase up to December 2012 and references of retrieved relevant articles.

Eligibility criteria for selecting studies Prospective cohort studies with relative risk and 95% confidence intervals for breast cancer according to fish intake, n-3 PUFA intake, or tissue biomarkers.

Results Twenty six publications, including 20 905 cases of breast cancer and 883 585 participants from 21 independent prospective cohort studies were eligible. Eleven articles (13 323 breast cancer events and 687 770 participants) investigated fish intake, 17 articles investigated marine n-3 PUFA (16 178 breast cancer events and 527 392 participants), and 12 articles investigated alpha linolenic acid (14 284 breast cancer events and 405 592 participants). Marine n-3 PUFA was associated with 14% reduction of risk of breast cancer (relative risk for highest v lowest category 0.86 (95% confidence interval 0.78 to 0.94), I2=54), and the relative risk remained similar whether marine n-3 PUFA was measured as dietary intake (0.85, 0.76 to 0.96, I2=67%) or as tissue biomarkers (0.86, 0.71 to 1.03, I2=8%). Subgroup analyses also indicated that the inverse association between marine n-3 PUFA and risk was more evident in studies that did not adjust for body mass index (BMI) (0.74, 0.64 to 0.86, I2=0) than in studies that did adjust for BMI (0.90, 0.80 to 1.01, I2=63.2%). Dose-response analysis indicated that risk of breast cancer was reduced by 5% per 0.1g/day (0.95, 0.90 to 1.00, I2=52%) or 0.1% energy/day (0.95, 0.90 to 1.00, I2=79%) increment of dietary marine n-3 PUFA intake. No significant association was observed for fish intake or exposure to alpha linolenic acid.

Conclusions Higher consumption of dietary marine n-3 PUFA is associated with a lower risk of breast cancer. The associations of fish and alpha linolenic acid intake with risk warrant further investigation of prospective cohort studies. These findings could have public health implications with regard to prevention of breast cancer through dietary and lifestyle interventions.

From press release:

A high intake of fatty acids found in fish is associated with a 14% reduction in the risk of breast cancer in later life, finds a study published on bmj.com today.

The results show that each 0.1 g per day or 0.1% energy per day increment of intake of n-3 polyunsaturated fatty acid (n-3 PUFA) derived from fish was associated with a 5% reduction in risk. To achieve this risk reduction, intake of oily fish such as salmon, tuna or sardines should be 1-2 portions per person per week.

Breast cancer is one of the most common cancers, accounting for 23% of total cancer cases and 14% of cancer deaths in 2008. Studies suggest that a healthy diet and lifestyle is crucial for the prevention of breast cancer, and dietary fat is one of the most intensively studied dietary factors closely related with risk.

The n-3 PUFAs include ALA, EPA, DPA and DHA. They are involved in chemical messaging in the brain, helping to regulate blood vessel activity and areas of the immune system. The main dietary sources of EPA, DPA and DHA come from oily fish, while ALA is found mainly in nuts, seeds, and leafy green vegetables.

Although n-3 PUFAs are the most promising types of fat to reduce cancer risk, results from human studies are inconsistent.

So a team of researchers based in China set out to investigate the association between fish and n-3 PUFA intake and the risk of breast cancer. Levels were measured from both dietary sources and blood tests.

They reviewed and analysed the results of 26 studies from the United States, Europe and Asia involving over 800,000 participants and over 20,000 cases of breast cancer.

Marine n-3 PUFA was associated with a 14% reduction of breast cancer between the highest and lowest category of marine n-3 PUFA intake. The risk was lowest in Asian populations, probably because fish intake is much higher in Asia than in western countries, say the authors.

Further analysis indicated a dose response: each 0.1 g per day or 0.1% energy per day increment of intake was associated with a 5% reduction in risk. However, no significant protective association was found for ALA -- the plant based n-3 PUFA.

The authors say their analysis, together with previous publications, "supports a protective role of marine n-3 PUFA on the incidence of breast cancer."

They conclude: "Our present study provides solid and robust evidence that marine n-3 PUFA are inversely associated with risk of breast cancer. The protective effect of fish or individual n-3 PUFA warrants further investigation of prospective studies."

Study Information

J.-S. Zheng, X.-J. Hu, Y.-M. Zhao, J. Yang, D. Li
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 June
Food Science and Nutrition, Zhejiang, China