On average we are about 1cm taller the morning than in the evening.
In simple words, when we sleep, our back is in a straight position, therefore backbone stretches. So when we wake up, our backbone is in a stretched position, and we are around 1 cm taller. But during the day and our activities, the backbone contracts. Thus, we are a few millimeters shorter after morning and throughout the day
Why does it happen?
When we sleep, our spine is no longer subjected to the pressures of gravity, and our body is able to replenish lost fluids between your intervertebral discs, which stretch and relax. The excess fluid provides up to 1 cm more of height upon waking.
This thing happens when astronauts travel to outer space. According to NASA research, astronauts gain up to 5 cm in height once they are freed from the gravitational pressure of Earth. We, however, don’t live on the outer space , and the earth’s gravity compresses our spines throughout the day, draining that extra fluid and shrinking our height.
Except for the backbone, the cartilage in our knees and other areas slowly compress, and the other component to this phenomenon is that the joint capsules loose some of their synovial fluid and the connective tissues around the joints tend to become compressed throughout the day from activity and trying to counter the affects of gravity.
Also, the discs of the spine do the same thing. During the night, they resorb more fluid making them thicker and the person taller. While walking or being upright during the day, they slowly lose some of this fluid and become thinner.
