When my grandmother was in her 70's her lumbar vertebrae crumbled due to osteoporosis, and she was wheelchair bound.   At the time she was maybe 5-10 lbs overweight.   In the years following, she lost about 25lbs (putting her at the lower end of a healthy weight).   Her logic was that if she weighed less there would be less pressure on her spine and she would be easier to care for when she needed help.  She lived until 93.