**2. The relationships among osteoporosis, renal function and periodontal disease**

Osteoporosis is the most common metabolic bone disease among the elderly, and the incidence of osteoporotic fractures obviously increases with age (Honig, 2010). In addition, elderly people often experience periodontal destruction. Because bone loss is a common feature of periodontitis and osteoporosis, both diseases may share some common etiologic factors (Offenbacher, 1996). The final expression of periodontitis is governed by complex interactions among host, microbial and environmental factors occurring within an intricate cellular mosaic (Offenbacher, 1996).

In addition, CRF is associated with marked disturbances of bone structure and metabolism, and there is a slowly progressive loss of renal function over months or years (Ruggeneti, 1998). A significant decrease in bone mineral density after transplantation is a serious finding (Huang & Sprague, 2009). It is well known that impaired renal function increases osteoclast activity leading to bone turnover, and this may influence bone metabolic parameters (Couttenye et al., 1999; Cirillo et al., 1998). There is a growing body of evidence indicating that impaired renal function is associated with disrupted regulation of vitamin D (Rix et al., 1999; Hamdy et al., 1995). Whereas some systemic factors that contribute to loss of bone mass and periodontal progression have been identified, we hypothesized that renal function is associated with bone metabolism, and thus is also associated with periodontal disease. To test this hypothesis, it is essential to evaluate the relationships among bone turnover, renal function and periodontal disease.

We initiated a longitudinal interdisciplinary study on aging (the Niigata Study) in 1998 to examine the many links between oral health and general health and well being. In the present report, we reviewed the relationship between bone metabolism and periodontal disease, taking renal function into consideration, in elderly Japanese subjects from the Niigata Study.
