Bone loss tied to autoimmune reaction.

Some call osteoporosis the "silent thief," because it reduces the density of bones, leaving them fragile and vulnerable to fracture. A preliminary study now hints that, at least in some cases, an autoimmune process causes osteoporosis.

Stephen D. Barnhill of the Medical College of Georgia in Augusta and his co-workers studied 27 women age 40 to 80 who were being evaluated for osteoporosis. The researchers discovered a direct relationship between loss of bone density and high concentrations of an enzyme linked to immune disorders and found in white blood cells.

Scientists know that most women lose bone mass during the five to 10 years after menopause. Certain women develop porous bones when their production of the female sex hormone estrogen declines. After menopause, Barnhill suggests, the estrogen receptors on cells, including bone cells, remain empty. This may trigger a complicated immune reaction that leads to the resorption of bone, he says.

"The initial data look very, very good," Barnhill adds. If additional research confirms the link between the immune system and osteoporosis, the team would like to try to block this rogue immune reaction, perhaps with a drug such as tamoxifen, which blinds with estrogen receptors.