It turns out that the majority of us undergo a measurable height change from waking up to the end of the day. While for most this change goes by mostly without notice, others can experience a shortening in the scale of inches.
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The measurement of two brothers in 2001 was performed by Tillmann and Clayton, two experts in children’s development from the University of Tartu. They quantified the height loss and found that most of the height “gained” overnight is thought to be lost in the first 3 hours of our day and maximal height loss is achieved by around 3pm.
The average change in height throughout the day is thought to be around 19mm. This is mostly attributable to changes in the height of our intervertebral discs. Our spine, as one might expect, is in fact not a long continuous bone. It is composed of 33 small bones called vertebrae. Spongy intervertebral discs lie between adjacent vertebrae in the spinal column. They have a role as shock absorbers preventing damage to the vertebrae themselves.
During sleep the loading (the amount of stress or pressure) on the spine is reduced. There is nothing preventing them from swelling and so they begin to absorb fluid and increase in volume. As the volume of the discs is increasing, they are of course also increasing in height. When we stand up and go about our daily tasks the loading on the spine is increased. The fluid will then begin to be expelled from the disc and it will decrease in size. Therefore, throughout the day the fluid content and height of the discs is variable. This leads to slight variation in height throughout the day.
These changes throughout the day may have a use in the diagnosis of lower back pain and sciatica. The time of the onset of symptoms and any changes in their severity throughout the day may be able to act as an aid in diagnosis. Lower back pain can be caused by a variety of problems including nerve irritation and degeneration of the intervertebral discs. Sciatica is pain from the lower back going down the leg. In 90% of cases it is due to the slipping of an intervertebral disc which will then push on any of the nerves that run from the back into the leg.
Research into using changes in height to aid diagnosis of these conditions was performed in 1990 by a group of bone specialists. They used dead bodies to investigate the effects of loading on the properties of intervertebral discs. They found that with increased loading, amongst other effects, disc prolapse becomes less likely and could explain why previous studies have found that ‘first episodes’ of back pain occurred in the early part of the working day and mine workers sustain spinal injuries more commonly in the morning.
Also, since different structures are more heavily loaded throughout the day, the time of onset of a patient’s symptoms, and any changes in their degree of severity over the day may help us to understand how their condition is working to affect the spine. For example, if most pain is felt in the morning when bending then the issue is probably due to the intervertebral disc. This is because most pressure is put on this structure in these conditions.
They also note that differences in lifestyle will affect the change in height. For example, a heavy manual labour job will induce a quicker change in height than a more sedentary lifestyle. In effect, lying on the sofa all day could make you taller!