Every year, your body replaces 20% of its bone calcium and you simply cannot afford to fall behind in this natural process.

The loss of bone calcium was limited to a total of 5 percent, he said.

After three years of treatment with either a testosterone or a placebo patch, the researchers will look for hormone-related improvements in muscle mass and strength, bone calcium and sense of well-being.

The researchers are trying to determine whether raising the men's testosterone levels to that of a 40-year-old will result in an enhanced sense of well-being and improved bone calcium, muscle mass and strength.

Although dietary calcium levels are adequate, absorption of dietary calcium is not always sufficient, given the intensity of production, to fully replenish bone calcium.

Elements of some other soft drinks - like phosphates, sugar and caffeine - have been examined individually and as part of the beverages and shown to increase the excretion of calcium in the urine, he said, but in the long run they have essentially no effect on bone calcium because the body makes adjustments.

They studied soil sedimentation and bone calcium for clues to whether he was ritually buried, or died in the place where he was found.

Physiologists described the effects on bone calcium of long periods of reduced body weight, and showed how a correct balance could be maintained by a specially selected diet and drugs.

Mr. Romanenko lost less than 5 percent of bone calcium in his 10 1/2 months in space, far less than had been expected.