Are you taller in the morning than at night?

Once you reach adulthood, your height is supposed to be a settled fact, written on your driving licence and never discussed again. But your body has not read the paperwork. Every single day, you shrink a little, and every night, you grow back.

The short answer

Yes, you are taller in the morning. Over the course of a normal day, people typically lose about a centimetre of height, and often a bit more, then regain it while lying down overnight. One study abstract presented to the Radiological Society of North America cites a normal daily loss of about 17 millimetres for the whole body.

The real story

Your spine is a stack of bones called vertebrae, separated by cushion-like intervertebral discs. Each disc has a tough outer ring and a softer, gel-like centre that holds a lot of water. When you stand, sit, walk and carry things, gravity and your own weight press down on those discs. Slowly, fluid is squeezed out of them and they get slightly thinner.

One disc losing a millimetre or so does not sound like much, but you have quite a few of them, and it adds up. In the RSNA study, researchers used MRI scanners to measure the five discs of the lower back in 32 men, once soon after waking and again after an 8 to 9 hour working day. Those five discs alone lost around 7 to 8 millimetres of combined height.

The loss happens surprisingly fast. Research summarised by ScienceBlog found that more than half of the daily shrinkage happens within the first hour after getting up, and around 80 percent within three hours. A study of adults in Ghana found an average morning-to-evening loss of about 1.6 centimetres, with the biggest losses linked to physically demanding work.

At night, when you lie flat, the pressure comes off. The discs soak fluid back up and plump out again, and by morning you are back to full height.

Space shows the effect at its most extreme. With almost no load pressing down on the spine, astronauts on long missions can grow up to about 3 percent taller, according to Scientific American. For someone 1.8 metres tall, that is around 5 centimetres. Back on Earth, gravity squeezes them back to normal within a few months.

Why people get it wrong

The change is too small to notice in the mirror, and almost nobody measures themselves twice in one day. We also get measured in very formal settings, at the doctor or for official documents, which makes height feel like a single fixed number. In reality it is more like a daily tide, going out during the day and coming back in at night.

So if you ever want to win an argument about who is taller, schedule the measuring for first thing in the morning. Just don’t tell the other person why.

“Me, I’m flat as a pancake morning and night, mate. Spend your life under a boot and you stop expecting a growth spurt.”