What precautions are advised for eating kale (collards)?

Kale is a powerhouse vegetable that is full of nutrients.  However, since it is a rich source of Vitamin K, if you are on an anticoagulant medication/blood thinner, eating Kale in large quantities might cause an interference.  If you are on an anticoagulant medicine, important to enjoy kale after discussing this with your physician.  Also, Kale is naturally high in oxalates which can interfere with calcium absorption.  It is best to avoid eating a calcium-rich food at the same time as kale.

Members of the cabbage family contain goitrogens, naturally occurring substances that can interfere with the functioning of the thyroid gland. Dietary goitrogens are usually of no clinical importance unless they are consumed in large amounts or there is coexisting iodine deficiency. Cooking helps to inactivate the goitrogenic compounds. Individuals with already existing and untreated thyroid problems may want to avoid consumption of cabbage-family vegetables in their raw form for this reason. Kale also contains significant amount of oxalate. Individuals with a history of oxalate-containing kidney stones should avoid overconsuming kale and other oxalate-containing greens.