Treatment is with reduced forms of folic acid. There is also a variation by strain for requirements of riboflavin, pyridoxal and folic acid. It resembles a component of folic acid. It acts by blocking the body's use of folic acid. Blackberries are also noted for containing manganese and folic acid. Pyrimethamine is classified as a folic acid antagonist. Women who may become pregnant are advised to get 400 micrograms of folic acid daily. A number of drugs interfere with the biosynthesis of THF from folic acid. Adequate intake of folic acid, and iron is often recommended. Preconceptional intake of folic acid is recommended to reduce birth defects. This enzyme is a critical component of the folic acid cycle. There are concerns that large amounts of supplemental folic acid can hide vitamin B deficiency. Other risk factors include diets low in protein, folic acid, and carotene. Tatsoi contains high levels of vitamin C, carotenoids, folic acid, calcium and potassium. Dietary supplementation of folic acid had been previously recommended by the WHO.