Salmon is recommended for breast cancer in moderation
Salmon is a good source of vitamin D, selenium and omega-3 polyunsaturated fatty acids, all of which have been associated with lower risk of certain cancers, including breast cancer. Salmon also appears to contain other compounds that may reduce cancer risk; one study identified a salmon protein hydrolysate that inhibited the growth of human breast cancer cells. Consumption of fatty fish or fish oil has been found to reduce the risk of coronary heart disease. Eating fatty fish such as salmon has been found to be associated with reduced risks of leukemia, multiple myeloma, and non-Hodgkin lymphoma, as well as renal cell, endometrial and prostate cancer.
Generally speaking, the benefits of consuming fatty fish, including salmon, are thought to outweigh the potentially detrimental effects of the toxins from pollution and other sources that tend to accumulate in their adipose tissue. Salmon is considered a low mercury fish. However, depending on its location, salmon can accumulate levels of polychlorinated biphenyls (PCBs), dioxin-like PCBs, polychlorinated dibenzo-p-dioxins, dibenzo-p-furans, chlorinated pesticides, mercury and methylmercury high enough to be detrimental to human health. Exposure to PCBs has been associated with increased risk of developing breast, prostate, testicular, ovarian and uterine cancers.
Wild salmon from the open ocean have been found to incorporate lower levels of these contaminants than farmed salmon. Wild salmon also have higher omega-3/omega-6 polyunsaturated fatty acid ratios than farmed salmon. This is because farmed salmon are fed a concentrated mix of fishmeal and fish oil that tends to be high in contaminants. Some of the farmed salmon feed now used is plant-based, partly in response to the contaminant problem and partly because it is less costly than fish oil. However, substituting vegetable oils in the farmed salmon diet reduces the omega-3/omega-6 fatty acid ratio, giving the fish a less favorable profile for breast cancer prevention. Food coloring is added to the feed because otherwise the salmon would not have the brilliant color of wild salmon. In addition, farmed salmon are treated with antibiotics, pesticides and hormones in the struggle to keep them growing and healthy in the massively crowded conditions of the pens in which they are raised. Therefore, wild salmon is a better choice than farmed salmon.
Breast cancer-related effects of eating salmon
Like other fatty fish, salmon contains marine fatty acids, in which there has been considerable interest. It is felt that these fatty acids probably have anticarcinogenic effects against breast cancer, especially since they have been shown to inhibit proliferation of breast cancer cells in the laboratory. One study found that the marine fatty acid docosahexaenoic acid enhances the cytotoxic effect of taxanes used in chemotherapy and reduces HER2/neu oncogene expression in human breast cancer cells. Another study found that docosahexaenoic acid increased survial times for almost half of a group of stage IV breast cancer patients on FEC (5-FU, epirubicin and cyclophosphamide), an anthracycline-based chemotherapy regimen. Fish protein hydrolysates also have been shown to have antiproliferative activity against human breast cancer cell lines in vitro. Not all epidemiological studies have found convincing evidence of a negative association between marine fatty acid intake or fatty fish consumption and the risk of breast cancer. However, several studies have found that higher omega-3/omega-6 polyunsaturated fatty acid ratios are associated with reduced risk of breast cancer and consuming wild salmon would tend to improve the ratio for most women.
Additional comments
Generally speaking, farmed salmon from the North Atlantic (including near Scandinavia) tend to have the highest levels of contaminants, Pacific North American farmed salmon have moderate levels, and Pacific South American farmed salmon have the lowest levels. However all farmed salmon have higher levels than the levels found in wild salmon. Based on fairly stringent toxin allowances, people can safely eat up to two servings of farmed salmon per month and up to eight servings of wild salmon. Removing the skin from salmon is recommended to reduce the level of contaminants ingested. Farmed salmon consumption should be avoided by pregnant women and nursing mothers due to its contaminant content.
Pan frying fatty fish has been shown to release carcinogenic heterocyclic amines (HCAs) in concentrations high enough to affect human health. Population studies have found that consumption of fried fish is associated with increased risk of breast cancer.
Arctic char is a high-omega 3 fatty fish related to salmon and is likely to have a similar health profile. However, much of the arctic char available in the U.S. is farm raised. Icelandic arctic char has a reputation for low levels of toxins.
Swordfish, bluefish, and black cod also contain relatively high levels of omega-3 fatty acids. Swordfish has among the highest levels of mercury of any available seafood and should for the most part be avoided. Bluefish has moderately high levels of mercury (approximately the level of whole albacore tuna). Canadian samples of black cod have also been found to have high levels of mercury. Very little of the cancer-related research that has been performed has included any of these three fish.
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