Calcium content of broccoli and kale: influence of the production method

A daily supply of 800 to 1200 mg Calcium in adolescence is crucial to prevent osteoporosis in the adult. Vegetarians are dependent on calcium rich vegetables. Recent research data indicate that the bioavailability of calcium from broccoli and kale is almost identical to that of milk. In our experiments broccoli and kale were grown in a hydroponic system and on soils rich and poor in calcium. Although calcium is stored primarily in leaves, increasing calcium content in the nutrient solution led to a maximum calcium concentration in the broccoli flower of 100 mg/ 100 g fresh weight. Conventionally grown broccoli flowers contained about 50 to 80 mg Ca/ 100 g fresh weight. Only about half of the calcium (250 mg/100 g) was stored in the leaves when broccoli was grown on a soil poor in calcium. Kale stored 350 to 400 mg calcium per 100 g fresh weight at the highest calcium content in the nutrient solution, and 250 to 400 mg calcium per 100 g fresh weight on calcium rich soil. Kale which was grown on a soil poor in calcium contained significantly less calcium (170 to 250 mg/ 100 g) even with additional calcium fertilization. Vegetarians should therefore preferentially consume vegetables grown on a substrate rich in calcium.