Calcium ingested at dinner is mostly absorbed and utilized by the body before bedtime. After sleeping, especially after midnight, the level of calcium in the blood will gradually decrease, the decline in blood calcium, promote the parathyroid gland hypersecretion, the hormone effect on bone tissue, so that part of the bone tissue calcium salts, dissolved into the blood, in order to maintain a stable balance of blood calcium. This dissolving effect is the body's self-regulation function, over time, will become one of the causes of osteoporosis. Drinking milk before going to bed at night, the calcium in milk can be slowly absorbed by the blood, the whole night blood calcium has been supplemented to maintain the balance, do not have to dissolve the calcium in the bone, to prevent bone loss, osteoporosis, so drink milk before going to bed is good.