LEP and osteoporosis: Breuil et al. (2011, 2014) also found that circulating OT levels correlated with osteopenia or osteoporosis in post-menopausal women. In particular, higher circulating levels of OT were associated with high bone mineral density (hip) in women with lower circulating levels of estradiol or higher circulating levels of leptin (Breuil et al., 2014). Similar to what is observed in OT and OTR null mice (Tamma et al., 2009) and in Col2.3Cre mice that lack OTRs in osteoblasts (Sun et al., 2019), humans with low OT serum levels display severe osteoporosis (Breuil et al., 2011).