Safety profile

Because of its high vitamin K content, patients taking anti coagulants such as warfarin are encouraged to avoid kale since it increases the vitamin K concentration in the blood, which is what the drugs are attempting to lower. This effectively raises the dose of the drug and causes toxicity. Its leaves contain 0.2 g/100 g of oxalic acid, a value far less than some other comparable greens such as spinach (0.97 g/100) and purslane (1.31 g/100 g). It may be used; however, with caution, even in individuals with known oxalate urinary tract stones. Adequate intake of water is advised to maintain normal urine output.