(HealthDay)—With research finding that the body prefers calcium from food, not supplements, it can be a challenge to meet daily requirements if you’re lactose-intolerant. On average, adults need about 1,000 milligrams of calcium a day. Fortunately, there are choices within many food groups that deliver on calcium. Leafy greens are a great calcium source, and at the top of the list are cooked spinach, collard...