Chapter 1. Introduction

Osteoporosis is a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture (Consensus development conference 1993). Typical characteristics of an osteoporotic stage are increased bone resorption in proportion to bone formation, reduced bone mineral density and decreased trabecular bone volume. Osteoporosis can be considered a major public health problem, causing over 1,3 million fractures and financial costs exceeding 10 billion dollars annually in the United States alone (Consensus development conference 1991). Osteoporosis is predicted to be an even greater problem in the future, due to the aging of the world population. Furthermore, the number of osteoporotic fractures, e.g. in Finland, is increasing more rapidly than can be accounted for by demographic changes alone (Kannus et al. 1995).

Since there are no effective, safe methods for restoring high quality bone to the osteoporotic skeleton, the prevention of osteoporosis is of utmost importance. Strategies for the prevention of osteoporosis consist of optimization of peak bone mass in early adulthood, and prevention of bone loss at menopause and with aging. Genetic, nutritional and life-style factors influence peak bone mass, and may be used in focusing the preventive efforts. An adequate calcium intake, good general nutrition and sufficient physical activity have been emphasized. From the current therapy modalities for the prevention of osteoporotic bone loss, most widely used are the treatments with estrogen (+progesterone), bisphosphonates and calcitonin.

On the grounds of recent studies, orally administred xylitol has some interesting properties that may be of use in the prevention of osteoporosis. Dietary xylitol supplementation in rats has been shown to increase calcium and phosphorus levels of bone (Knuuttila et al. 1989), to promote the restoration of bone calcium content during rehabilitation following dietary calcium deficiency (Hämäläinen et al. 1990), and to protect against the ovariectomy induced loss of bone mineral content during experimental osteoporosis (Svanberg & Knuuttila 1994).

However, before any conclusions can be drawn about the usefulness of a compound, studies including structural evaluation and biomechanical testing of the bones must first be performed. Thus, the present study was performed in order to clarify the effects of dietary xylitol supplementation on bone resorption, on bone trabeculation, and on bone biomechanical properties in healthy rats, and during experimental osteoporosis.