Osteoporosis in neurodegeneration.

Osteoporosis affects bone microarchitecture and reduces bone mass. There are more than 200 million people with osteoporosis worldwide, and the prevalence is slowly increasing. The highest prevalences are found in Scandinavia and USA, also slowly increasing. A parallel increase in neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis, and multiple sclerosis has been noted since the middle of this century. Osteoporosis is more common in patients with each of these neurodegenerative conditions than in the general population. Several metals with neurotoxic properties accumulate in bone and can substitute for calcium in hydroxyapatite, the main mineral component of bone. Especially cadmium, but also lead, aluminum and arsenic affect bone mineral density negatively. Metals with neurotoxic properties have also been found in brain and cerebrospinal fluid from patients with Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis, and multiple sclerosis, and markers for neurodegeneration such as amyloid beta peptide and amyloid precursor protein have been detected in bone tissue from patients with osteoporosis. A common mechanism contributing to the pathogenesis of both neurodegeneration and osteoporosis can be suspected. The hypothesis that neurodegenerative disorders are associated with osteoporosis is presented and discussed.