The short answer

Standing and moving load the spine during the day. Intervertebral discs change under that load, so standing height can decrease and then recover after time lying down. This normal daily variation is one reason repeated measurements should be taken at a similar time.

How large can the change be?

The number is not identical for everyone or every study. In a study of 53 children measured during a school day, most of the decrease happened during the morning: the mean loss was about 0.31 cm from 9:00 to 11:00 and another 0.20 cm from 11:00 to 13:00, with little additional change from 13:00 to 15:00.

A separate intensive case study of one adolescent recorded an average morning-to-bedtime decrease of about 0.98 cm. Small studies in adults have observed larger trough-to-peak changes, but those figures should not be treated as a universal “normal amount” for a teenager.

What it does not mean: being taller after sleep does not mean your leg bones grew overnight, and being shorter in the evening does not mean you lost adult-height potential.

How this affects tracking

If one height is measured immediately after waking and the next is measured late in the day, the difference can disguise or imitate a small change. For a cleaner series:

  • measure at roughly the same time of day;
  • use the same wall and equipment;
  • record the time with the measurement;
  • focus on longer-term patterns rather than day-to-day fluctuations.

Can stretching make the morning height permanent?

Stretching can change posture or a measurement in the short term, but the child study above found that a “stretched” measuring technique did not remove daily variation. A temporary measurement difference should not be marketed as permanent skeletal growth. Read the full guide to stretching, hanging and height.

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