Herring and sardines are recommended for breast cancer in moderation
In the U.S., herring are often consumed as sardines, which are either young herring or small fish that are members of the herring family. Scandinavians and some Asian populations have relatively high rates of herring consumption, and many of the pickled or salted herring food products available in the U.S. are imported from those regions. Herring is a good source of Vitamin D, coenzyme Q10, selenium and omega-3 polyunsaturated fatty acids. Generally speaking, the benefits of consuming fatty fish are thought to outweigh the potentially detrimental effects of the toxins from pollution and other sources that tend to accumulate in their adipose tissue. Sardines contain fewer toxins than full grown herring. Consumption of fatty fish or fish oil has been found to reduce the risk of coronary heart disease. Intake of oven-baked herring has been shown to increase HDL cholesterol (i.e., the "good" cholesterol). However, note that several Danish studies and an Icelandic study have found that high fatty fish intake during pregnancy (presumably from fish caught in the region) was inversely associated with fetal growth, apparently because of polychlorinated biphenyls (PCBs) concentrations in the fish. In addition, a Norwegian study found elevated levels of PCBs in the breast milk of women who regularly consumed fish.
Swedish studies have found that the consumption of fatty fish (such as herring and salmon), but not lean fish (cod and flounder), was associated with lower risks of endometrial cancer, renal cell carcinoma, non-Hodgkin's lymphoma and chronic lymphocytic lymphoma. Eating fatty fish such as herring has also been found to be associated with reduced risks of leukemia and multiple myeloma, as well as endometrial and prostate cancer.
Breast cancer-related effects of eating herring and sardines
Like other fatty fish, herring contains marine fatty acids (including docosahexaenoic acid) 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 Her-2/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 (5FU, 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 herring would tend to improve the ratio for most women. A study of Finnish fishermen and their wives found that while their high fish consumption appeared to reduce mortality overall (despite high intakes of environmental contaminants in the fish), it did not reduce mortality from cancer in the women. A Swedish study comparing the breast cancer rates of two large groups of fishermen's wives found a lower risk of breast cancer for those residing on the west coast of Sweden compared to the east (Baltic) coast, where the fish are known to be contaminated with more organochlorine compounds.
Additional comments
Anchovies are also members of the herring family and are a good source of omega-3 fatty acids. Drained filleted anchovies packed in oil have more vitamin A and vitamin E than similarly packaged sardines, but less vitamin D. However, anchovies usually have a great deal of sodium, which makes them inappropriate for those who need to limit their salt consumption, and in any case not suitable as a regular source of omega-3 fatty acids for breast cancer patients and survivors.
We recommend against consuming all but modest amounts of pickled or dried herring, since such preserved fish foods have been associated with increased risks of gastric, colorectal and other cancers.
Pan frying 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.
Herring consumption should be reduced or eliminated by pregnant and nursing mothers since toxins from pollution and other sources have been found to reduce birth weight and are secreted in breast milk.