X-rays of old C57BL/6J male mice showed deformed vertebral columns. Bone density was found to increase between 76 and 517 days of age and to decrease after 685 days of age. The boron content of femurs declined by 9% with aging but the decrease was not significant. Calcium increased between 76 and 198 days of age but declined by 36% between 200 and 1000 days of age. Iron increased by 207% by 1000 days of age. Copper declined between 76 and 198 days of age but increased by 61% between 200 and 1000 days of age. Bone collagen as indicated by hydroxyproline and proline content decreased 17.4% by 1000 days of age. The largest single change with aging was, therefore, in the iron content of bone. Several correlations were found to be independent of the age of the animals. Bone density was correlated with bone calcium and collagen. Iron was negatively correlated with calcium and collagen. Calcium and collagen content were unrelated. Bone density and iron were also suprisingly unrelated. A possible explanation for this observation is given. Copper was negatively correlated with bone calcium, bone density, and collagen content. Excess copper was, therefore, the single most important factor associated with decreasing bone size and density.
