Cancer is taking over the reins of command in almost every country worldwide with the startling changes in the environment and eating patterns. Earlier, we came across cancer as a rarity in people and treatment course offered was also not advanced enough to help people survive and extend their lifespan. But now, it has become a well-established disease with advancements in treatments, care and extension of life. There are people across the world suffering from various forms of cancer with certain types dominating the male and female populations respectively. Women are often victims of breast, cervical, ovarian and skin cancer with breast cancer being the leading cause of death in women accounting for almost 23% of cancer cases worldwide. The disease can affect any woman but the risk increases as the individual grows old and there are certain other factors too that puts some women at a greater risk than others. We have numerous studies showing that a healthy diet and lifestyle are critical for the prevention of breast cancer, the absence of which has also increased the risk of this cancer form in many women.
Food as a Factor Against Cancer Risk
The studies that quote dietary factors as a weapon against cancer also show that dietary fat is one of the closely studied dietary factors related to breast cancer risk. Among all the dietary factors, n-3 polyunsaturated fatty acids (n-3 PUFA) is appreciated for its inherent property to curtain carcinogenesis and reduce cancer risk as seen in rodent models and in vitro cell studies. We do have the Singapore Chinese Health Study and the Japan Collaborative Cohort Study that show an inverse link between dietary fat (PUFA) intake and breast cancer risk but certain other observational studies are also inconclusive. Fish, the favorite seafood of many, is an excellent source of PUFA but studies show an inverse or positive association with cancer risk. This brings us to a very important juncture here whether fish intake, PUFA’s major dietary source, affects breast cancer risk in any way.
Fish: A Fulfilling Source of Nutrition
Fish is one of the healthiest foods available to mankind on this planet and is an integral part of a healthy diet. Eating fish replenishes one with abundance of omega-3 fats apart from other nutrients such as vitamin D, selenium and protein. We have quite a few studies displaying the authentic advantages of consuming fish which include protecting the heart from diseases, improving blood vessels functioning and easing inflammation. Physicians and health experts suggest eating fish at least twice a week but not all individuals follow this quoting different reasons-a dislike in taste, not knowing how to prepare or fearing toxin presence such as mercury and pesticide residues.
Effect of Fish Intake on Postmenopausal Women
A report by the World Cancer Research Fund in 1997 portrayed that eating fish reduced the risk of colon, breast, rectum and ovary cancer. But we have different studies reporting different conclusions and given below is a study on postmenopausal women and the effect of fish consumption on their breast cancer risk. The study included 29,875 women aged between 50 and 64 years residing in Denmark who were asked to report on their dietary intake through a 192-item food frequency questionnaire (FFQ) through mail. The participants were asked to answer choosing any of the 12 different options given for each question ranging from never to 8 or more times a day. While foods such as fruits, beverages and breads were calculated in pieces, glasses or slices portion sizes of other foods were calculated by multiplying frequencies with portion sizes. OF the 192 foods mentioned 24 of them pertained to different types of fish. A lifestyle questionnaire was also given with questions on parity, age of birth of first child, history of benign breast tumor surgery and so on. Many participants were excluded based on different criteria such as cancer diagnosis right before study, experienced menstruation or did not provide complete information which left the research team with 23,693 women.
The study team analyzed fish intake according to fat content differentiating them as lean (≤8 g fat/100 g fish) and fatty (>8 g fat/100 g fish) and method of preparation (fried (8 questions), boiled (5 questions) and processed (11 questions)). Processed fish were taken as a separate group as the preparation method differs here which includes pickling, salting and smoking. All the participants ate between 11 and 86 g of fish with lean fish consumed more than fat fish. The method of preparation was mostly fried or processed and consumption of boiled fish was low. The study showed that total fish intake was associated with a significant increase in breast cancer incidence rate per 25g daily intake. The team divided total fish intake into quartiles and on comparison of the upper quartile group with the lower quartile group there was an increase of 47% in the incidence rate of breast cancer. Also, to analyze whether incident rate ratio (IRR) was associated with fat content the research team divided fish intake according to fat content. Results showed IRR values of 1.11 and 1.13 for fatty fish and lean fish. Finally, the research team concluded that high total fat intake rather than fat content and preparation method was associated with increased incidence of breast cancer.
European Prospective Investigation
European prospective investigation into cancer and nutrition (EPIC) study is a vast study on diet, lifestyle and environmental factors conducted across 10 European countries on 5,19, 978 participants. Collection of data on dietary habits and lifestyles were via questionnaires on all the participants who were between 35 and 70 years of age. Of them, 366,521 were women of whom many of them were excluded due to various reasons such as prevalence of cancer at the time of recruitment, failure to fill questionnaire or provide complete information. This left the study team with 2,77,834 women.
The study team analyzed total fish consumption (whole fish and molluscs), total lean fish consumption and total fatty fish consumption. Any fish that had less than 4% fat is classified as lean fish (such as cod, haddock) and one that has more than 4% fat is considered as fatty fish (salmon, trout and herring). Results showed that fish consumption was associated with a slight increase in breast cancer risk in some countries, France, the country with the longest follow-up and most breast cancer cases did not show any protective effect nor any increase in risk between fish consumption and breast cancer risk. Women in the top quintile of fatty fish showed a positive association with breast cancer risk but when analysis for both lean and fatty fish consumption was conducted there was no association with breast cancer risk. There are other epidemiological studies that analyzed the association between n-6/n-3 ratio and breast cancer risk but results are contradictory. Three studies that analyzed fatty acids in serum phospholipids or erythrocyte membrane found no association while three other studies that analyzed n-3 and n-6 in adipose tissue showed inverse association with breast cancer.
Meta-analyses of Cohort Studies
A meta-analysis of observational studies was done to understand where exactly fish consumption stands in cancer risk and a search was conducted in the PubMed and Embase database using a set of keywords to extract the relevant studies. Search came up with 215 different publications of which 26 of them were found to be eligible. 11 studies from eleven independent cohorts showed a positive link between fish intake and risk of breast cancer with 13,323 cases of breast cancer and 6,87,770 participants but dose-response analysis did not show a positive link for breast cancer risk for 15 g/day increment in fish intake. 17 articles from 16 independent cohort studies showed an association between n-3 PUFA and breast cancer risk that involved 16,178 breast cancer events and 5,27,392 participants. PUFA intake was inversely associated with breast cancer risk. 8 of the 17 articles were eligible for dose-response analysis whose results showed that a 0.1 g/day increase in n-3 PUFA was associated with a 5% lower risk of breast cancer. 12 articles that involved 14,284 cases of breast cancer and 4,05,592 participants were involved in analyzing the association between ALA exposure and breast cancer risk. There was no association found between ALA intake and breast cancer risk and this was true even in the case of dose-response analysis.
PUFA intake was inversely associated with breast cancer risk in both Asian and Western with the results more predominantly seen in the Asian population. Hence, this meta-analysis shows that high intake of n-3 polyunsaturated fatty acids is linked with 14% reduction in breast cancer risk and with 0.1 g/day increment of intake there was a 5% reduction in risk. This encouraging news is a platform for researchers to take up the research to the next level on finding more information about fish intake and reduction in breast cancer risk.
Fish Intake is Positively Associated with Breast Cancer Incidence Rate: https://academic.oup.com/jn/article/133/11/3664/4817947
Fish Consumption and Breast Cancer Risk. The European Prospective Investigation into Cancer and Nutrition: https://onlinelibrary.wiley.com/doi/full/10.1002/ijc.21819
Intake of Fish and Marine N-3 Polyunsaturated Fatty Acids & Risk of Breast Cancer: meta-analysis of Data from 21 Independent Prospective Cohort Studies: https://www.bmj.com/content/346/bmj.f3706
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