The plant contains the carcinogenic compound ptaquiloside. Ptaquiloside is known to cause haemorrhagic diseases in ruminants, tumours and haematological problems in non-ruminants, and is correlated with oesophageal and gastric cancer in humans. Chronic bracken consumption is also associated with upper digestive tract (UDT) squamous cell carcinomas in cattle (ruminants)—with the most aggressive and serious tumors located in the caudal (lower) UDT. High stomach cancer rates are found in Japan and North Wales, where the young stems are used as a vegetable, but it is unknown whether bracken plays any part or if the cancer can be attributed to another cause. Consumption of ptaquiloside-contaminated milk is thought to contribute to human gastric cancer in the Andean states of Venezuela. The spores have also been implicated as carcinogens. Consumption of contaminated water and meat may be dangerous as well. However, ptaquiloside is water-soluble, and is reduced by soaking bracken in cool water. Korean and Japanese cooks have traditionally soaked the shoots in water and ash to detoxify the plant before eating. Ptaquiloside also degenerates at room temperature, which explains why the rat studies were done with the toxin stored at −20 °C (−4 °F). At boiling temperature, the carcinogen denatures almost completely. Salt and baking soda also help with volatilizing the chemical. It has been suggested that selenium supplementation can prevent as well as reverse the immunotoxic effects induced by ptaquiloside from Pteridium aquilinum.