During the three daily meals in the daytime, the human body can intake 300-400 milligrams of calcium. When the body's calcium regulation mechanism is activated and excess calcium is excreted in urine, the blood can be replenished from food to maintain calcium balance. However, at night, calcium is still excreted, but there is no calcium supplement from food. As a result, a portion of calcium in the blood is released to compensate for the loss of urinary calcium. To maintain a normal calcium level in the blood, the body must draw upon its calcium reserves, namely, the calcium in the bones. This regulatory mechanism means that most of the calcium in the morning urine comes from bone calcium.
On the other hand, various hormones that regulate calcium metabolism in the human body have different secretion patterns day and night. Generally, blood calcium levels are lower at night and higher during the day. The hypocalcemia at night may stimulate the secretion of parathyroid hormone, accelerating the breakdown of bone calcium. If a calcium supplement is taken appropriately before bedtime, it can provide sufficient "ammunition" for the night, preventing the body from mobilizing bone calcium.
Therefore, consuming milk or other calcium-rich foods or supplements before bedtime is the most effective.