Salmon is a good source of astaxanthin, choline, niacin, vitamin B6, 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. 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 to 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 to omega-6 fatty acid content, giving the fish a less favorable profile for breast cancer prevention. Food coloring is often 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 the marine fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which have chemopreventive properties. These marine fatty acids have been shown to inhibit proliferation of breast cancer cells in the laboratory. Relatively high fatty fish intake has been shown to be associated with reduced risk of breast cancer and improved survival. In one experiment, higher omega-3 to omega-6 fatty acid diets reduced mammary gland density in mice, which in turn reduced carcinogen-induced mammary tumor development. Fish oil has been shown to inhibit early stages of mammary tumor development in a mouse model of HER-2/neu overexpressing (HER2+) breast cancer. DHA has been demonstrated to reduce bone metastasis in a mouse model of breast cancer. 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) chemotherapy. Fish protein hydrolysates also have been shown to have antiproliferative activity against human breast cancer cell lines in vitro.
Many epidemiological studies have found convincing evidence of a negative association between DHA and EPA intake or fatty fish consumption and the risk of breast cancer, although not all are in agreement. In addition, several studies have found that higher omega-3 to omega-6 fatty acid intakes are associated with reduced risk of breast cancer; consuming wild salmon would tend to improve this ratio for most women.
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.
In November 2015, the U.S. Food and Drug Administration (FDA) approved genetically modified farmed salmon to be sold in the U.S. without any labeling requirements. The salmon grows to market size in as little as half the time as non-engineered salmon. The GMO salmon contains a growth hormone gene from the Chinook salmon and a genetic switch from the ocean pout (an eel-like sea creature), that ensures that the transplanted gene is continuously active. Normal salmon growth hormone gene is active only parts of the year. Although the FDA has declared the fish safe for human consumption, it will take years to gain meaningful information on the consequences to human health of consuming it.
Salmon sashimi, nigiri and other raw salmon preparations should be avoided since they have the potential to cause infection with parasites. In early 2017, it was reported that some wild Pacific salmon are infested with tapeworm larvae.
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.
Below are links to recent studies concerning this food. For a more complete list, including less recent studies, please click on salmon.