Intake of Fish and Omega 3s and Breast Cancer Survival

Khankari NK, Bradshaw PT, Steck SE, et al. Dietary intake of fish, polyunsaturated fatty acids, and survival after breast cancer: A population-based follow-up study on Long Island, New York. Cancer. 2015;121:2244-2252.

The primary objective of this study was to explore whether dietary omega-3 polyunsaturated fatty acid (PUFA) intake from fish and other sources benefits survival after breast cancer in a group of women who were newly diagnosed with first primary breast cancer.

This is a follow-up study from a population-based study. 

This study was conducted in Long Island, New York, among 1,463 women newly diagnosed with first primary breast cancer. Women were interviewed approximately 3 months after initial diagnosis to assess risk and prognostic factors, including dietary intake (using a food frequency questionnaire). The 2 primary diagnoses were a first primary in situ (16%) or invasive breast cancer (84%.) At the time of diagnosis, women ranged in age from 20 to 98 years and 67% were postmenopausal; 94% identified their race as white, 4% as black, and 2% as other. This is reflective of racial distribution in the counties in which data was collected. 

For this study, authors used resources from a population-based follow-up study conducted on Long Island, New York, among 1,463 women newly diagnosed with first primary breast cancer.

 

Participants self-completed a food frequency questionnaire (FFQ) administered at baseline that assessed dietary intake for the year before the interview. PUFA intake from any dietary sources was estimated by linking participant responses from the FFQ (g/day for each food item), with the average nutrient values for foods available in the United States Department of Agriculture Database for omega 3 and 6 PUFAs. The following PUFA subtypes were estimated: 

 

An estimated total intake of omega 3 and omega 6 was calculated by summing each individual fatty acid within its respective category. Seafood consumption was also assessed by the FFQ and was differentiated by either being fish- or shellfish-based.

 

Other factors assessed included demographics, reproductive and menstrual history, exogenous hormone use, family history of breast cancer, body size, physical activity, alcohol and cigarette use, occupational history and environmental exposures, and other basic medical history. 

Vital status was determined through December 31, 2011, yielding a median follow-up of 14.7 years and 485 deaths, 210 of which were breast cancer–specific. Participants’ deaths were determined via a linkage with the National Death Index, a standard epidemiologic resource used for attaining mortality data. Women were identified who died from all causes (death from any cause) and also women who died from breast cancer specifically. 

 

In the statistical analyses, quartiles were created for PUFA exposure (total PUFA, total omega 3, ALA, EPA, DHA, DPA, total omega 6, LA, ALA, and the ratio of omega 3 to omega 6.) In Cox proportional hazard models, there was also consideration between total omega 3 and 6 intakes and between the omega 3/6 ratio in association with mortality. Effect modification of the association between PUFA intake and mortality by menopausal status, hormone receptor status, dietary supplement use, treatment, and BMI were also examined in PUFA regression models. 

In this population-based study of women with breast cancer in Long Island, New York, there was an observed reduction of 16% to 34% in all causes of mortality after 15 years of follow-up for women with a diet high in fish and the long-chain PUFAs EPA, DHA, and DPA. Based on the FFQ responses, on average women had a total omega 3 intake of 0.99 g/day, with ALA intake being the highest contributor with an average of 0.85 g/day. Average omega 6 intake was much higher, with an average 7.51 g/day. LA was the highest contributor at an average intake of 7.44 g/day. Fish was the primary contributor to the high intake of long-chain omega 3 PUFAs, while foods like muffins, biscuits, and fried foods contributed to the shorter-chain omega 3 ALA. A diet high in omega 6, specifically AA, was linked to foods such as eggs and meat. 

 

Statistical analysis indicated that survival was improved in women with breast cancer who reported a higher intake of the long-chain omega 3s EPA, DHA, and DPA (quartiles 3 and 4) compared with those in the lower quartile. Fish intake specifically was associated with a 25% to 34% reduction in all-cause mortality. Separately, lower rates of death were observed for those in the highest quartile of tuna intake compared with those with no intake and compared to the highest quartiles for other fish intake (broiled/baked). There was no evidence of association for all-cause mortality and shellfish intake. Adjusted estimates for breast cancer–specific mortality demonstrated a pronounced reduction (19%) when tuna and other fish intake was assessed in relation to 5 years of follow-up. There did not appear to be an observed relationship with the omega 3/omega 6 ratio and outcome measures.

This study appears to be the first study to examine a potential relationship between PUFA intake and breast cancer survival. Naturopathic doctors and other integrative practitioners routinely change their patients’ diets as a foundational element of a treatment plan, particularly in individuals with a cancer diagnosis. This study provides evidence to support the addition of foods with omega-3 fatty acids, both shorter- and longer-chain, to provide some risk reduction for all causes of mortality in women with a history of breast cancer. 

 

The omega-3 foods in this study were from both marine (seafood) and nonmarine sources, although fish appeared to be most beneficial. A healthy, balanced diet should consider both. Foods naturally higher in preformed long-chain PUFAs, such as EPA and DHA, include fatty fish such as salmon and tuna. While this study did not look specifically at dietary supplementation, preformed EPA and DHA can also be found in fish oil, krill, and algal oil supplements and should be considered for those who do not eat fish.