Posture and measured height

Why the number on the wall changes through the day, how much a bent spine costs, and why none of it is bone.

Measured height is not one number

You are taller in the morning than at night, by around two centimetres. Nothing about your skeleton changed. The discs between the bones of your spine hold water, standing up squeezes some of it out through the day, and lying down lets it back in.

The height you measure is your skeleton plus whatever the soft tissue between the bones is doing at that moment.

• Stature varies by about 1.1% over a day, 19.3 mm in a study of eight young adults. 54% of that is lost in the first hour after getting up, and most of it returns in the first half of the night (Spine, 1985)
• The mechanism is spinal loading. Intervertebral discs are mostly water held by the same kind of fixed charge that makes cartilage swell (see Aggrecan and matrix sulfation), and body weight presses some of it out over the hours you spend upright
• The cycle reverses nightly whether or not you do anything about it. It is a load effect, not growth
• A height measured at 9am and one measured at 9pm are not comparable. Measure at a consistent time, or the daily swing can be larger than the change you are trying to detect

A bent spine measures shorter

A spine that curves forward or sideways holds your head lower than a straight one would. Straightening it brings that height back. Surgeons who correct severe spinal deformity have measured how much, and the numbers are large — but they come from an operation that fuses the spine, and a quarter of those patients ended up shorter. For an ordinary slouch the figure is about a centimetre.

The clearest measurement of what alignment is worth comes from the extreme end: adults having spinal deformity corrected surgically, with full-body radiographs before and after (JBJS, 2023).

• In 198 patients, mean age 57, 147 of them (74%) gained height; a quarter were shorter afterwards. Among those who gained, mean full-body gain was 7.6 cm — the figure is the average of the ones it worked for, not of everyone operated on
• It came from two places: 3.8 cm from the trunk and 3.3 cm from the lower body, which tracked the corrections in pelvic tilt and overall sagittal balance. Neck and head accounted for under 6 mm between them
• A 1° correction in a thoracic scoliosis Cobb angle gave about 0.2 mm of height, and 1° in a thoracolumbar curve about 0.25 mm
• None of that is available without the operation. These were people with deformity severe enough to fuse a spine for, the lower-body share came from standing them up at the pelvis and hips rather than from anything in the back, and the Cobb angle measures a sideways curve while a slouch is a forward one. The number for an ordinary posture is far smaller: in 28 healthy young adults, going from relaxed to fully upright standing added 1.3 cm in men and 0.8 cm in women (Physiother Theory Pract, 2013)
• A straighter spine measures taller because the head sits higher, not because any bone is longer

Stretching, hanging and inversion

Hanging from a bar or lying on an inversion table unloads the spine, so you measure taller afterwards. It is the same water moving back into the same discs, and it leaves again when you stand up. Sleeping does it more thoroughly.

• Unloading the spine reverses the daily compression early. That is a real, measurable change in stature, and a temporary one
• There is no good evidence that stretching, hanging or inversion produces a lasting increase beyond restoring what loading took. The claim that they add height is the main thing sold in this area, and it rests on the temporary effect being measured and presented as a permanent one
• Strengthening work aimed at a slouched posture targets your usual standing height rather than your peak one. In older women with low bone mass, 8 months of heavy resistance and impact training reduced thoracic kyphosis (Osteoporos Int, 2019), and in an early report on 28 of them added 0.4 cm of measured height while controls lost 0.3 cm (Osteoporos Int, 2015)
• Once the growth plates have closed, no amount of any of this lengthens bone (see Oestrogen for what closes them)

What this is and is not

All of this recovers height you already have. None of it creates any.

• The skeleton sets a ceiling. Posture determines how much of that ceiling you stand at on a given day
• For most people the effect is 1 to 3 cm: about 2 cm across the day from the discs (Spine, 1985), and about 1 cm between relaxed and fully upright standing (Physiother Theory Pract, 2013)
• If you are still growing, this sits alongside the pathways in the rest of the library. If you have finished growing, it is the only part that is still moving

Educational content, not medical advice. Nothing here is a recommendation to take or stop taking anything — talk to a doctor about your own situation.