Eating salted fish frequently will greatly increase the risk of nasopharyngeal cancer

Nasopharyngeal cancer is a cancer with a very low incidence rate. In European and American countries, the incidence rate is about one in 100,000. However, it particularly favors people in South China. Data shows that the incidence rate in South China is between 10 and 20 per 100,000 men, and 5 to 10 per 100,000 women. In some areas of Guangdong, it is even as high as 50 per 100,000.

In 1970, some scholars proposed that this phenomenon might be the result of the interaction of three factors: different genes, early infection with EBV virus and eating salted fish. EBV is a relatively widespread virus, not unique to South China, so it has not attracted much attention. As for genes, some epidemiological surveys have found that people in South China still have a high incidence of nasopharyngeal cancer after immigrating to the United States, Canada and other places; but the incidence of their descendants began to decline. Researchers believe that this is due to the fact that the descendants of these immigrants gradually gave up the lifestyle of their ancestors. Therefore, genetic factors are not so noteworthy.

The research focused on salted fish. However, it is not easy to study the impact of diet on cancer - at least, humans cannot be used as control experiments. Most studies are "case-control" surveys. The most complete one was a survey of Hong Kong youth published in 1986. That study found 250 nasopharyngeal cancer patients as "cases" and asked them to provide a relative or friend of similar age and gender, thus obtaining 250 "controls" without nasopharyngeal cancer.

Through question-and-answer sessions, they were asked to provide information about their work and life, and their mothers were asked about their diet composition during childhood. Finally, the study obtained 127 sets of "case-control" data. By analyzing these data, it was found that the most significant factor leading to nasopharyngeal cancer was eating salted fish during childhood.

Of course, this does not mean that eating salted fish will definitely cause nasopharyngeal cancer, but eating salted fish in childhood will greatly increase the proportion of nasopharyngeal cancer. After statistically analyzing the collected data, the authors of this study believe that "more than 90% of nasopharyngeal cancer patients among young people in Hong Kong are caused by eating salted fish, especially eating salted fish in childhood." Several other "case-control" studies also support the conclusion that salted fish increases the risk of nasopharyngeal cancer. Therefore, the International Agency for Research on Cancer (IARC) classifies Chinese salted fish as a Class 1 carcinogen, meaning that there is sufficient evidence to support its carcinogenicity to humans. Similar results can also be observed in mouse experiments.