A study published in the Journal of Bone and Mineral Research found that postmenopausal women who regularly had five hours or less of sleep a night had lower bone mass and were twice as likely to have osteoporosis of the hip and spine, compared with women who slept about seven hours nightly. The researchers used data from 11,084 participants of the Women's Health Initiative Study and found that women who slept for six hours every night had a slightly increased spine and whole-body osteoporosis risk.