Kale Drug Interactions, Uses, Effectiveness, Safety & More

Kale is a leafy green vegetable in the cabbage family (the same family as broccoli, cauliflower, and Brussels sprouts). It comes from the plant Brassica oleracea and is grown widely in cool climates around the world. There are several types, including curly kale, lacinato (also called dinosaur or Tuscan) kale, and red Russian kale.

People most often eat kale as a regular vegetable, raw in salads, cooked in soups and stir-fries, baked into chips, or blended into smoothies and juices. It is also sold as a dried powder and in capsules as a 'green' supplement.

Kale is valued mainly for its nutrition. It is low in calories and packed with vitamins, minerals, fiber, and plant compounds that act as antioxidants.

Kale contains several groups of compounds that may explain its possible health benefits. These include antioxidant vitamins (vitamin C and beta-carotene), glucosinolates (sulfur compounds found in cabbage-family plants that the body can convert to substances studied in cancer research), and carotenoids like lutein and zeaxanthin that concentrate in the eye.

Its fiber may support digestion and help with cholesterol and blood sugar control as part of a balanced diet. Vitamin K plays a role in normal blood clotting and bone health.

It is important to know that many of the disease-related mechanisms come from laboratory or animal research, or from studies of the isolated compounds rather than whole kale. These findings do not guarantee the same effects in people.

Eaten as a normal food, kale is safe and healthy for most people. A few groups should be thoughtful about how much they consume.

Kale is high in vitamin K, which is involved in blood clotting. People who take certain blood thinners need to keep their vitamin K intake steady rather than suddenly eating much more or less (your pharmacist or doctor can guide you on this).

Kale is a goitrogenic vegetable, meaning very large amounts—especially raw—may affect thyroid function in people who are prone to thyroid problems or are low in iodine. Cooking reduces this effect. Normal food portions are not a concern for most people.

Kale also contains oxalates, which can contribute to kidney stones in people who are prone to them. Pregnancy and breastfeeding: kale as a food is nutritious and considered safe; concentrated kale supplements or very high doses have not been well studied, so check with your provider before using them.

For most people, kale causes few problems. Because it is high in fiber and sulfur compounds, eating large amounts can cause gas, bloating, or stomach upset.

Raw kale and kale juice in large quantities may bother the digestive system more than cooked kale. People prone to kidney stones may want to limit very high oxalate intake. Allergic reactions are rare.

If you notice any unusual or severe reaction after greatly increasing your kale intake, stop and talk to a healthcare professional.

There is no established 'dose' of kale because it is a food, not a standardized medicine. As a vegetable, it can be included as part of a balanced diet the way you would eat any leafy green.

For kale powders, capsules, or juices, no proven therapeutic dose exists. Follow the directions on the product label, and remember that a concentrated supplement can deliver much more vitamin K and other compounds than a normal serving of the vegetable.

If you take medications, have thyroid or kidney problems, or are pregnant, check with your pharmacist or doctor before using concentrated kale supplements.