The cruciferous vegetable is just like broccoli, cauliflower, and Brussel sprouts a member of the cabbage family. Kale is one of the most nutrient-dense foods in existence.

Kale is especially rich in vitamin K and the minerals calcium and magnesium. Ample research supports those nutrient's role in bone health. Kale has also plenty of other nutrients that are important for bone health: vitamin C, vitamin A, manganese, copper, iron, and potassium.

Research has suggested that a high intake of vitamin K may help reduce the risk of bone structures. The study was conducted over 10 years and included a total of 1,114 fractures cases and 80,982 participants. (1) Only one cup of cooked kale contains 544 μg of vitamin K (453% DV). Vitamin K2 plays an important role in the metabolism of calcium – the main mineral found in the bones. An increased intake of vitamin K2 could be beneficial in lowering calcium-associated health risks. (2)

Dark, leafy greens such as kale are high in calcium. One cup of cooked kale (130 g) contains 94 mg of calcium (9% DV). Also, magnesium is a vital nutrient in bone mineralization and maintenance of bone integrity. A magnesium deficiency contributes to osteoporosis directly by acting on crystal formation and bone cells. (3) One cup of cooked kale contains 23 mg of magnesium (6% DV).

Next to its great nutritive value, kale also offers a high antioxidant activity. (4) Food high in antioxidants may reduce the risk of many diseases. Antioxidants neutralize free radicals from the body cells and prevent or reduce the damage caused by oxidation. Kale contains high amounts of sulfur, which helps produce glutathione, one of the most important antioxidants in the body. Kale also contains lutein and zeaxanthin, which function as antioxidants in the body and improve eyesight. Lutein is known to improve or even prevent age-related macular disease which is the leading cause of blindness and vision impairment. (5)

Kale contains numerous cancer-fighting substances. Some studies have pointed out a positive correlation between cancer prevention and the consumption of cruciferous vegetables such as kale. (6)

The flavonoid quercetin which is found in large amounts in kale showed to be beneficial for lowering blood pressure, especially in individuals with hypertension (high blood pressure). ouble-blind, placebo-controlled, crossover trial showed that supplementing with 730 mg of quercetin a day for 28 days consistently reduced the blood pressure of participants with hypertension compared to a placebo. (7)

References:

1. Hao, G., Zhang, B., Gu, M., Chen, C., Zhang, Q., Zhang, G., & Cao, X. (2017). Vitamin K intake and the risk of fractures: A meta-analysis. Medicine, 96 (17), e6725. https://doi.org/10.1097/MD.0000000000006725

2. Maresz K. (2015). Proper Calcium Use: Vitamin K2 as a Promoter of Bone and Cardiovascular Health. Integrative medicine (Encinitas, Calif.), 14(1), 34–39.

3. Castiglioni, S., Cazzaniga, A., Albisetti, W., & Maier, J. A. (2013). Magnesium and osteoporosis: current state of knowledge and future research directions. Nutrients, 5(8), 3022–3033. https://doi.org/10.3390/nu5083022

4. Sikora, E., & Bodziarczyk, I. (2012). Composition and antioxidant activity of kale (Brassica oleracea L. var. acephala) raw and cooked. Acta scientiarum polonorum. Technologia alimentaria, 11 (3), 239–248.

5. Buscemi, S., Corleo, D., Di Pace, F., Petroni, M. L., Satriano, A., & Marchesini, G. (2018). The Effect of Lutein on Eye and Extra-Eye Health. Nutrients, 10(9), 1321. https://doi.org/10.3390/nu10091321

6. Murillo, G., & Mehta, R. G. (2001). Cruciferous vegetables and cancer prevention. Nutrition and cancer, 41(1-2), 17–28. https://doi.org/10.1080/01635581.2001.9680607

7. Larson, A. J., Symons, J. D., & Jalili, T. (2012). Therapeutic potential of quercetin to decrease blood pressure: review of efficacy and mechanisms. Advances in nutrition (Bethesda, Md.), 3(1), 39–46. https://doi.org/10.3945/an.111.001271