The big question: People are taller in the morning

Q. Is it true we are taller in the morning?

A. Yes. New Scientist magazine says there are two components to our height first thing in the morning.

In the growing child, growth hormone is secreted in pulses overnight. This acts through several intermediary steps to cause lengthening of the bones at the end-plates (epiphyses). Accurate measurements of the forearm or lower leg using specialised apparatus or x-rays can record this night-time growth.

The most marked effect, however, occurring even after growth has ceased, is caused by postural compression of the spine under gravity. This was recognised in medieval France - people applied to join the army first thing in the morning in order to appear taller. In 1724, a Northamptonshire parson, the Rev Joseph Wasse, measured a loss of up to 6/10 inch (15mm) through the day. This was more marked in young, active labourers. As his horse showed no shoulder-to-hoof shrinkage after a long gallop, he rightly assumed the shrinkage was due to compression of the intervertebral discs.

Modern height measurements are taken at the same time of day, when possible, with a stretching force applied to the head to minimise postural loss. The curvatures within the spinal column vary with body weight and position and tend to press downwards when in an upright position, shortening the spinal length. Lying down, the reverse happens and the column lengthens again.

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