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I've heard this claim quite a few times and have even repeated it as fact. The basic claim is that 'gravity compresses the spine' during the waking hours and since (most people) sleep at night, they are tallest first thing in the morning.

I can find examples of the claims online - many with answers - but most are from non-reputable sites without sources. In my own personal experience, I believe this to be true; but I would like something more official than my own experience to support my claim (or I'd like to know that I'm wrong).


Examples:

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What do you mean by taller? What is the smallest measurable difference in length that you are willing to accept as "taller"? Fact is that if I take a foot long horizontally oriented steel rod and hold it up vertically, it gets shorter in the Earth's gravitational field. (I just can't prove it with any equipment that I have on hand, of course.) Since your joints contain compressible, elastic material, you must be taller not just in the morning, but instantaneously taller whenever you recline. –  Kaz May 1 '12 at 4:51
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up vote 44 down vote accepted


Yes, we are taller in the morning.


From The transformation of spinal curvature into spinal deformity (2005):

The effects of gravity on the upright human posture are powerful: Individuals are as much as 25 mm taller in the morning than in the evening (1)(2), as a result of compressive forces bearing down all day,

And astronauts 'grow' by nearly 75 mm when released from the force of the earth's gravity (3).


From NASA (2004):

Did you know that astronauts are up to 2 inches taller while they're in space? As soon as they come back to Earth, though, they return to their normal height.

To some degree, a similar stretching of the spine happens to you every night. When you lie down, gravity isn't pushing down on your vertebrae.

You can do your own experiments with a meterstick. Measure your height carefully as soon as you get up or while you are still lying down. You will find that you're about a centimeter or two taller.

That's not as much as astronauts change in space. The idea, however, is the same. As the day passes, your vertebrae compress through normal activities, and you'll lose those few centimeters you "grew" overnight.

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Great answer, great references. Anyone that doubts this should measure themselves! –  jozzas Apr 30 '12 at 22:42
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@jozzas: They should measure themselves anyway! There's a widespread phenomena of not really knowing your own height. –  Oddthinking Apr 30 '12 at 23:30
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I notice this when adjusting my rear view mirror. I always have to adjust for my slight increase in height in the morning as compared to where the mirror ended up the evening before. –  Mark Adler May 1 '12 at 6:25
    
@MarkAdler yep, that's what first had me thinking about this too. –  Ste May 2 '12 at 15:31
    
@Mark: Could that be more of a slouched posture when you are tired issue? –  Oddthinking May 28 '12 at 22:47
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This topic is actually discussed in a physics lecture found on MIT OpenCourseWare. You can enjoy Prof. Walter Lewin do an experiment showing that a person is taller laying down vs. standing up:

http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-1

The relevant part starts at about 5:20

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Maybe you should also tell the result of the experiments for those who don't want/care/have time/etc. to watch the video –  nico May 28 '12 at 18:28
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