Scientists are testing a hormone found in salmon see if it can prevent thinning of bones in older women.

About 20 million postmenopausal American women suffer from osteoporosis, which causes bones to lose calcium and become thin and brittle. This leads to fractures, often of the hip, and collapse of vertebrae.

The salmon hormone, called calcimar, is believed to help prevent bones from losing calcium. It is similar to a human hormone called calcitonin.

Calcimar "is not at present thought of as a cure for the disease," says nutritionist Gail Butterfield of Stanford University, one of 10 centers performing clinical trials with the hormone. Rather, she says, it is "a treatment to prevent or slow down any further deterioration."

Human calcitonin cannot be obtained for use as a drug, Butterfield says. "You can't grind up humans and get human calcitonin."

There are as yet no centers in the Washington metropolitan area participating in the test, according to a spokesman for USV Laboratories, a division of the Revlon Health Care Group, which is running the program.

Osteoporosis often leads to death. About 15 percent of women with hip fractures die within three months from complications.

Men also can suffer osteoporosis, but much less frequently.

Meanwhile, a study in Finland suggests that fluoride, put in drinking water to prevent tooth decay, also appears to prevent osteoporosis.

Researchers from the National Board of Health of Finland compared two towns -- Kuopio, which has fluoridated water, and Jyvaskyla, which does not. "The lower incidence of fracture in Kuopio suggests that fluoride is an essential mineral for the strengthening of bone tissue," researchers Olli Simonen and Ossi Laitinen write in the British medical journal The Lancet.

The water in Kuopio contained about 1 part fluoride per million, the same level used in Washington area drinking water. Such a level is "near the optimum concentration for the prevention of bone fragility," they write.