The American Council on Science and Health discussed calcium in its June 2001 publication "The Role of Milk in Your Diet," published on its website:

“All foods in the ‘milk, yogurt, and cheese’ food group are rich in calcium. So if you include enough foods from this group in your daily diet, you are assured of getting a reliable source of calcium every day. In the other food groups, however, only a few of the many possible choices are high in calcium. For example, only a few vegetables (such as spinach, collard greens, and broccoli) are calcium-rich; most other vegetables (including such favorites as potatoes, tomatoes, lettuce, corn, and carrots) are not. In addition, the calcium in dairy products is better absorbed from the digestive tract than the calcium from some other sources… Milk and dairy products are good sources of many nutrients, and they are the best food source of the mineral calcium.”

June 2001