Cadmium may speed bone loss in women.

Cadmium may speed bone loss in women

Cadmium exposure may speed bone loss in postmenopausal women and may be one factor leading to osteoporosis, a porous bone disease that afflicts about 20 million Americans. The new research may help explain the increased risk of osteoporosis faced by older, female smokers exposed to cigarette smoke, which contains cadmium.

Many factors contribute to osteoporosis, which frequently strikes women who experience a drop in estrogen due to menopause. Estrogen is the female sex hormone that, among other things, protects against bone loss. The body is constantly tearing down and rebuilding bone. Victims of osteoporosis lose more bone than they replace and eventually have such porous bones that normal activities can lead to a fracture.

Cadmium has been linked to postmenopausal bone disease in Japan, where women living in the Jintsu River basin developed a painful bone disease known as Itai-Itai (which means Ouch-Ouch). Epidemiologic studies in the 1960s pointed to cadmium as a causative factor. The women lived downstream from a zinc and lead mine that had dumped cadmium into the river water, which was used for drinking and irrigating rice paddies. Even though men, young women and children were exposed to the cadmium, 95 percent of Itai-Itai cases developed in post-menopausal Japanese women.

Maryka H. Bhattacharyya, a bio-chemist at the Argonne (Ill.) National Laboratory, and colleagues speculated that cadmium may accelerate bone loss in menopausal women who lack estrogen's protective effect. To test their theory, the research team developed an animal model. They fed female mice diets containing cadmium chloride at either 0.25, 5.0, or 50 parts per million (ppm). The 0.25 group received an amount of cadmium that is biologically equivalent to human environmental exposure. The 5.0 ppm mice got amounts roughly equal to that ingested by the Itai-Itai victims. Mice getting 50 ppm cadmium got 10 times the Japanese exposure. After one year, the mice either had their ovaries surgically removed to mimic the onset of menopause, or got a sham procedure in which the ovaries were left in place.

In the November PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES (Vol. 85, No. 22), the researchers report the 50 ppm cadmium diet caused "significant" bone loss in mice without ovaries. Calcium contents of the femurs and vertebrae of these mice were "strikingly lower than those of nearly all other groups," the authors report.

In a separate part of the study, the team bathed fetal rat bone in a medium that contained cadmium in amounts similar to that found in smokers' blood. The cadmium cultures showed a 70 percent loss of bone as compared with a 25 percent loss for control samples. The finding suggests cadmium directly stimulates bone loss.

The new finding provides a plausible explanation for the fact that female smokers experience more bone fractures and tooth loss than nonsmokers. Smoking is known to boost bone loss by decreasing estrogen levels, but Bhattacharyya's work suggests the cadmium in smoke enhances that effect.