what causes older people to begin to “shrink” with time?

Question: what causes older people to begin to "shrink" with time?
- Keywords:
  older people,
  shrink,
  time
Asked by anon-174145 to Yewande on 21 Jun 2018.
- Yewande Oyekenu answered on 21 Jun 2018:
  
  Not only old people shrink. People can begin to shrink or get shorter from age 30-70. It happens because the bones shrink due to loss of fluid. To avoid shrinking, one should drink enough water and get enough night rest.

Question: what causes older people to begin to "shrink" with time?