Why do we get shorter as we age? First of all, I want to make it clear, I am
talking about your height, or how tall. I am Dr. John Shim and I hope you have already
had the opportunity to review my video’s about basic spine anatomy and why disc’s
degenerate. Understanding those concepts are helpful to understanding the explanation the
common question of “why do we get shorter as we age?”. Besides the spine, there are
other reasons why we get shorter, but we will concentrate strictly on the spine.
In the Disc degeneration video, the concept of disc dehydration, and the resultant narrowing
of the disc space was presented. As the animation will demonstrate, the once tall, normal sized
disc of our youth will give way to a dehydrated, bulging and narrowing disc. The disc height
can reduce significantly. The vertebral body sandwich, or functional
spine unit is composed of the vertebral bodies alternating with the intervertebral disc.
There are some population differences, but most collected anatomy data indicate a normal
disc height for men averages about 11 mm, and women 9 mm.
Population studies have definitely demonstrated a narrowing, and degeneration of the discs
with age. Interestingly, not every disc in every person will narrow. But in General,
the disc narrowing will occur in almost every person. The current conventional wisdom is
that after age 40, we shrink an average of ¼ to 1/3 of an inch every decade.
In addition to the disc decrease, there is another effect secondary to the change of
the shape of the disk, and the functional spine unit. When young, the spine has a natural
three smooth visible curves orientation. The neck, or cervical spine gently curves backward.
The upper back, or thoracic spine curves forwards. The lower back or lumbar spine curves backwards.
The backward curves are called lordosis. The forward curve is called kyphosis. In the normal
situation, the head is balanced over the pelvis, and this allows the most efficient use of
body energy to maintain property body mechanics and orientation.
As the discs degenerate and narrow, it causes the the lordotic curves to straighten, and
the kyphosis to become more curved. As a result, to keep the head positioned over the pelvis,
often times, the knees and hips need to be slightly bent to maintain the proper position,
and balance. This change of posture also results in the “shortening or shrinking of the height”.
Osteoporosis can also be a significant contributing factor to shortening. The bones collapse,
causing loss of height, and also causes more kyphosis. As discussed before, the body must
compensate for this kyphosis by again bending at the hips and knees.
As you now understand, the disc degeneration process leads to shrinkage or shortening by
both a reduction in height, and a change of the posture to achieve a balanced position.
Osteoporosis can also make a significant impact on the height.
There are other factors that contribute to shrinkage like loss of cartilage height in
our hips, and knees, or falling of our arches in our feet. But as a spine surgeon and specialist,
I can say the most significant factor causing age related shrinkage is your spine.
I hope you have a better understanding of this process. This is Dr. John Shim. Thanks
you for your attention.