Chocolate contains the stimulant caffeine (about 25 milligrams in one bar), which inhibits the absorption of calcium. Protein, sugar, sodium, and alcohol have also been shown to decrease absorption. Caffeine is also present in coffee and tea, favorites of most college students. Women in their twenties should consume at least 650 milligrams of calcium per day. Good sources are milk, yogurt, hard cheeses, tofu, spinach, collard greens, and salmon. If your diet does not meet this daily requirement, you should consider taking a supplement. Consuming sufficient calcium is important to ward of osteoporosis and to maintain bone strengthas it is the key component of bone tissue.