The movement of fluids in and out of the intervertebral disc plays a diurnal role on our varying stature.
Over the course of the day we lose 1.1% body height to be regained from sleeping.  This change is as a result of the spinal disc heights as they take-on fluid over a typical 8hr sleep and 16hrs of daytime activity. As the spine is under compression, the discs lose water, thought to be escaping through the vertebral endplates and with decompression the water was thought to be coming in through the same way. Investigations have demonstrated that the annulus fibrosus is also permeable to water flow via 360 degrees as the endplate mainly has permeability through its centre. 
Disc Height and Fluids
Measuring fluid flow in and out of the disc is difficult to do but disc height and associated creep can be experimentally measured. To get a closer look into this, a group of researchers led by Vergroesen published an article in the Journal of Biomechanics titled: The poro-elastic behaviour of the intervertebral disc: A new perspective on diurnal fluid flow. They believed that too much attention was being attributed to endplate fluid flow and did not take into account the full intervertebral disc as is relates to disc height loss and gains.
What they found was interesting and does have implication for those treating disc through manual or mechanical means. They believed their results warranted a new hypothesis demonstrating that fluids inflow occurs quicker when unloaded compared to outflow when the spine is loaded. With this information, a lie down during the day might be a wise decision as part of a treatment plan for those with back pain and associated disc height loss.
This type of research gives spine professionals a better perspective on symptom presentation and treatment strategies. Using a dynamic model helps to explain the diurnal variations of the spine and the mechanical strategies to make things better.
 Tyrrell, A.R., Reilly,T.,Troup, J.D., 1985. Circadian variation in stature and the effects of spinal loading. Spine10,161–164(Phila.Pa.1976).
 McMillan, D.W., Garbutt,G., Adams,M.A., 1996. Effect of sustained loading on the water content of intervertebral discs : implications for disc metabolism. Ann. Rheum. Dis.55,880–887.
 Nachemson, A.L., 1981. Disc pressure measurements. Spine 6,93–97, Phila.Pa.1976.