Japan has done the most in-depth research on the carcinogenicity of bracken. It was first discovered that there was a substance called protopterin in bracken, which was also discovered by the Japanese.

An epidemiological study was conducted in the 199s, which showed that eating a lot of bracken in childhood would also increase the risk of stomach cancer in adulthood. Such epidemiological studies have been done in Japan, Britain and other parts of the world, and the results are similar. Even in some places where bracken is abundant, because cows eat bracken grass, the milk produced may contain a small amount of protopterin. However, milk needs high temperature sterilization, which can greatly reduce the carcinogen content in bracken.

Yun Wuxin, a popular science writer, a member of the Scientific Squirrel Society and a doctor of food engineering, paid attention to the carcinogenesis of bracken several years ago. He pointed out that "bracken causes cancer" is supported by solid scientific evidence. Eating bracken will lead to a higher incidence of esophageal cancer and gastric cancer, and the "protofern glycoside" in bracken is the chief culprit of the above symptoms. As early as more than 1 years ago, people noticed that this plant can cause poisoning and even death of cattle, and animal experiments also confirmed that fern can really cause cancer in animals.