Is salted fish carcinogenic?

How certain foods, nutrients, and eating patterns influence cancer risk is of great interest. Although there is no certainty that eating more or less of single foods or nutrients guarantee cancer protection, there is no doubt that diet is an important consideration.

For example, most researchers agree that the strongest cancer protection comes from diets that include a variety of vegetables, fruits, whole grains, and other anti-oxidant-rich foods. While it is difficult to prove that the consumption of specific foods increases or decreases cancer risk, regional variations in cancer prevalence could be due to diet-related factors. For example, some studies have found a pattern between the occurrence of nasopharyngeal carcinoma and consumption of Chinese-style salted fish intake early in life.

Early studies reported a dose-dependent relationship between frequency and duration of consumption, and an association between salted fish intake during childhood compared to intake at older ages. Nonetheless, gaps in the research remain. For instance, previous studies evaluated the frequency of consumption, but not portion size. It also remains to be established if “soft” and “hard” subtypes of Chinese-style salted fish confer different risks due to distinct preparation methods.

To address these gaps, a recent study by Donal Barrett (Karolinska Institutet) and colleagues, investigated the associations of intake between Chinese-style salted fish types and intake of other preserved foods during adulthood, adolescence, and childhood with risk of nasopharyngeal carcinoma in a large-scale population-based case-control study set in 2 southern Chinese provinces where nasopharyngeal carcinoma is endemic.

The case-control study, published in the September 2019 issue of The Journal of Nutrition, included a total of 2244 confirmed nasopharyngeal carcinoma cases and 2309 controls. Subjects completed the same food frequency questionnaires for both adult and adolescent dietary assessment periods, reporting of consumption and overall actual portion size for 9 food categories. Chinese-style salted fish consisted of both “hard” and “soft” subtypes.  The “hard” subtype is prepared by directly salting and then drying; the “soft” subtype undergoes a decomposition phase and softening before salting and drying. Information on other preserved foods was also collected.

The researchers found no association between nasopharyngeal carcinoma and intake of hard Chinese-style salted fish during adulthood, and an increased risk at the highest level of intake during adolescence. A decreased risk of the middle intake level of soft salted fish during adulthood and adolescence was also found. Preserved foods showed contrasting risk profiles such that the highest adult intake level of salted egg was associated with increased risk of nasopharyngeal carcinoma but fermented black beans was associated with reduced risk. Associations with nasopharyngeal carcinoma were weaker than previously reported for weekly childhood intake of salted fish.

These results suggest that hard and soft salted fish have different cancer risk profiles. Salted fish and other preserved foods presented the weakest risk factor associated with nasopharyngeal carcinoma in all life stages, and therefore may play a smaller role in nasopharyngeal carcinoma occurrence than previously thought.

Reference Barrett D, Ploner A, Chang ET, Liu Z, Zhang C, Liu Q, Cai Y, Zhang Z, Chen G, Huang Q, Xie S, Cau S, Shao J, Jia W, Zheng Y, Liao J, Chen Y, Lin L, Ernberg I, Adami H Huang G, Zeng Y, Zeng Y, Ye W. Past and Recent Salted Fish and Preserved Food Intakes are Weakly Associated with Nasopharyngeal Carcinoma Risk in Adults in Southern China. The Journal of Nutrition, Volume 149, Issue 9, September 2019, Pages 1596–1605, https://doi.org/10.1093/jn/nxz095

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