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; many of the herring products available in the U.S. are imported from those regions.
Sardines are an excellent source of calcium since their bones typically are not removed before consumption. Herring and sardines are very good sources of the marine omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), and good sources of choline, selenium, vitamin B6, vitamin B12, and vitamin D. Herring incorporate more vitamin B6 and vitamin B12 than sardines. Both types of fish are also a source of coenzyme Q10 (CoQ10). Most of these compounds have been associated with lower risk of cancer, including breast cancer.
Consumption of fatty fish such as herring 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). Several Swedish studies have reported that consumption of fatty fish (such as herring and salmon), but not lean fish (such as cod and flounder), is associated with lower risks of endometrial cancer, renal cell carcinoma, non-Hodgkin's lymphoma and chronic lymphocytic leukemia. Eating fatty fish such as herring has also been found to be associated with reduced risks of endometrial and prostate cancer, as well as multiple myeloma.
Herring and sardine contaminants
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. Both are considered low mercury fish, since they are small fish far from the top of the food chain. Large, longer-lived fish accumulate mercury over time as a result of preying on smaller mercury-contaminated fish. Based on their low mercury status, people can safely eat up to two six-ounce servings of herring or sardines per week.
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.
Packaged herring has occasionally been recalled because of contaminants with the potential to cause acute illness, including by Listeria, norovirus and botulism. For example, a California company issued a recall in December 2020 for “Veladis herring in oil with Italian spices” due to Listeria contamination. While such recalls are not frequent, consumers should pay attention any such news.
Breast cancer-related effects of eating herring and sardines
Human studies
Relatively high fatty fish or marine fatty acid intake has been shown to be associated with reduced risk of breast cancer and improved survival, but not all studies are in agreement. 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.
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 or sardines would tend to improve this ratio for most women. Higher omega-3 to omega-6 fatty acid diets reduced mammary gland density in mice in one experiment, which in turn reduced carcinogen-induced mammary tumor development.
Marine omega-3 fats
EPA and DHA have been shown to inhibit proliferation of breast cancer cells in the laboratory. Fish oil (which typically consists primarily of EPA and DHA) 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.
Marine fatty acids have been found to enhance the therapeutic effects of tamoxifen and chemotherapy drugs such as Adriamycin (doxorubicin) and Taxol (paclitaxel).
Calcium
While several studies have reported an inverse association between calcium intake and risk of breast cancer, not all studies are in agreement. Low calcium intake is associated with increased breast density, a strong breast cancer risk factor. Calcium has been shown to have antiproliferative effects on breast cancer cells in the laboratory and to inhibit the development of mammary tumors in mice. However, more than one study has reported that relatively high levels of calcium in benign breast tissue is associated with a modest increase in breast cancer risk.
The link between calcium and breast cancer may be obscured by the fact that levels of calcium in the blood of breast cancer patients can be elevated because of effects of breast tumors on calcium homeostasis. Also, some women at high risk for breast cancer have subclinical hyperparathyroidism, which elevates calcium levels. In fact, both increases and reductions of cellular calcium levels appear to have the potential to increase the malignancy of a cell, depending on a variety of circumstances. For example, ongoing hypercalcemia (high circulating calcium) can induce changes in breast cancer cells that promote metastasis to high calcium microenvironments.
Nevertheless, based on available population studies, moderate to high dietary intake of calcium, especially in childhood and young adulthood, does not appear to promote breast cancer and might be protective against it. Note that use of supplemental calcium has not been found to be associated with reduced breast cancer risk.
Additional comments
Anchovies
Anchovies are also members of the herring family and are a good source of omega-3 fatty acids, selenium, calcium and vitamin D. Drained filleted anchovies packed in oil typically have more vitamin E than similarly packaged sardines, but less vitamin D. However, packaged anchovies and anchovy paste (normally made with anchovies, olive oil, vinegar, and salt) usually have a great deal of sodium, which makes them inappropriate for those who need to limit their salt consumption and not suitable as a regular source of omega-3 fatty acids for breast cancer patients and survivors.
Pickled and dried herring
We also recommend against consuming all but modest amounts of pickled herring such as rollmops or dried herring such as tuyo, which usually have high sodium content. Such preserved fish have been associated with increased risks of gastric, colorectal and other cancers.
Fried fish
Pan frying fish has been shown to release carcinogenic heterocyclic amines (HCAs) in concentrations high enough to affect human health. Population studies have reported that consumption of fried fish is associated with increased risk of breast cancer.
BPA and other exposures from canned sardines
Canned sardines can be a significant source of exposure to the breast carcinogen bisphenol A (BPA), an endocrine disruptor. BPA and similar compounds such as BPS appear to be associated with increased risk of breast cancer and its progression. BPA that has leached from food packaging and containers is the main source of exposure. Sardines packaged in glass containers may preclude this exposure, as long as the coating on the interior of the lid does not incorporate BPA.
Canned sardines, which typically are lightly smoked, also tend to be high in salt, depending on in the type of liquid in which they are packaged. Sardines packed in water or olive oil are often the best choice. Those in tomato or mustard sauce may have more additives. In any case, it's important to check the nutrition label.
Sources of information provided in this webpage
The information above, which is updated continually as new research becomes available, has been developed based solely on the results of academic studies. Clicking on any of the underlined terms will take you to its tag or webpage, which contain more extensive information.
Below are links to 20 recent studies concerning this food and its components. For a more complete list, including less recent studies, please click on herring.