There is a difference between the height measured in the morning and the height measured in the evening. The height measured in the morning will be about 1.5-2 cm higher than the height measured in the evening. This phenomenon is mainly related to the intervertebral discs between the spinal bones. The human spine is composed of 33 vertebrae and 23 intervertebral discs. The thickness of the intervertebral discs accounts for about 1/4 of the entire length of the spine. The lumbar disc is the thickest, accounting for about 1/3 of the length of the lumbar segment, and the thoracic disc and cervical disc account for about 1/5 of the thoracic and cervical segments, respectively. There is a jelly-like tissue in the intervertebral disc, which is clinically known as the nucleus pulposus, and the nucleus pulposus contains more water, about 75%-90%. During weight-bearing activities during the day, the nucleus pulposus evenly shares the weight of the body, which can cause the water in the nucleus pulposus to seep into the vertebral body under pressure, and the nucleus pulposus will flatten and the height will decrease, resulting in the phenomenon that the height measured in the morning will be higher than the height measured in the evening.