Nutrition for Enhancing Bone Volume in Mice

It is well known that postmenopausal osteoporosis is related to severe decreases in the serum estrogen levels. Estrogen deficiency produces an imbalance in the bone remodeling balance which is associated with a reduced bone volume and higher fracture risk. Androgen deficiency also produces osteoporosis by directly affecting bone cells. In addition, androgen was demonstrated to be present during the fetal period, and it is considered to play an essential role in the sexual differentiation of males. Therefore, both sex hormones, androgen and estrogen, are great important for bone homeostasis not only in females but also in males. This is further supported by the fact that both males and females express androgen receptor (AR), estrogen receptor-alpha (ER) and estrogen receptor-beta (ER). Androgen and estrogen react with the AR and ER and ERrespectively. It is thus speculated that they mutually regulate themselves during bone development and remodeling. Up to present, various studies have examined the roles of estrogen and its receptors to explore potential methods for preventing or treating postmenopausal osteoporosis (Judd et al., 1983; Kousteni et al., 2002; Martin-Milan et al., 2010; Pietschmann et al., 2008). Recent clinical studies have reported that the prevention of hip bone fractures and vertebral deformities is highly pertinent to improving the quality of life for older people (Chang et al., 2004; O’Neill et al., 2009). To avoid these incidents, we have to try to achieve adequate peak bone mass during adolescent growth, it is also important to understand the bone growth, because this is currently an under-investigated area. In adult animal experiments, orchiectomy and ovariectomy reduced both the bone volume and density. Furthermore, the bone volume loss was induced not only in the long bones but also in the mandibular condyles (Fujita et al., 2001). In addition, we have reported that these phenomena were also shown in immature mice (Fujita et al., 2006). Therefore, the influence of sex hormones on bone remodeling has been demonstrated in the craniofacial region. In orthodontic and orthopedic treatment, it is especially, difficult to predict bone growth including craniofacial and mandibular growth during adolescence. The full nature of bone growth, in association with sex hormones remains to be fully elucidated. The ratio of osteoporosis patient in Japan based on the diagnosed by Japanese society for bone and mineral research is reported 24% of over fifty-year-old people and it is indicated the number of patients is higher than those in USA and European countries (Orimo, 2000).