Increased bone density is not usually a normal process. A slightly higher than average bone density may be found in gymnasts or other athletes, but a much higher bone density than average is not normal. Increased bone density can be across the whole spine or just in specific areas. When the bone density increases abnormally, it is usually associated with some sort of disease or illness.
A May 2007 article in the "International Journal of Sports Medicine" reported on a study comparing the bone density of young athletes to their non active counter parts, showing an increase in bone mass in the active children. Further investigation also proved activities requiring larger muscle mass, high amounts of impact on the body and constantly fighting the forces of gravity had the largest effects on increased bone density. Gymnasts, martial artists and soccer players had a higher bone mass than swimmers or bicyclists.
Paget's disease is a rare bone disorder in which the cells that help build and destroy bone, go into overdrive, resulting in enlarged weakened bone. The Merck Manual states that this disease is usually found incidentally when looking at x-rays. The areas most commonly affected are the spine, pelvis and long bones of the arms and legs. The bone becomes larger and appears denser, but it is actually not as strong as regular bone.
Certain types of heavy metal poisoning over time will lead to an increase in bone density. Toxipedia, an online source for science information, mentions that high levels of fluoride over time will lead to severe joint pain and show osteosclerosis, or areas of increased density, on x-ray.
This is a rare form of inherited bone disease, according to the American Academy of Family Physicians. There are three main forms of this disorder, with the mildest form only being caught incidentally on radiographs. All forms of the disease cause a problem with resorption of bone, leading to sclerotic or dense malformed bones. The more severe forms of this disease are also accompanied by mental retardation and occasionally failure to thrive.
Melorheostosis is a rare and progressive disorder characterized by a thickening of the cortical bone in such a way that x-ray reveal a melted candle wax appearance. Not only does melorheostosis affect bone, but it affects soft tissue, as well. There is no known cause for this disorder and no treatment. The disease is progressive often affecting the hands or feet to the point of deformity, according to the Melorheostosis Association.