Aging of bone density in the second metacarpal.

Bone weight, bone and cortical areas, and apparent and true bone densities (W/BV and W/CV) were measured on the second metacarpals of 114 male and 114 female Japanese, aged 30 to 98 years. Measurements were taken from midshaft cross-sections 2 mm thick, using an electron balance and an image analyzing system. The mean values of these variables were greater in men than in women at all ages. Bone area stayed almost unchanged regardless of age. Bone weight and cortical area decreased linearly with advancing age. The respective rates of decrease per decade observed for the these variables were 3.1% and 2.9% in men and 5.5% and 4.8% in women. Apparent bone density decreased gradually with age after the fourth decade in women. While, in men, it stayed almost unchanged or increased slightly until the fifth decade and then, decreased gradually with age. The rate of decrease per decade was accelerated after the fifth decade in women and after the sixth in men, being 10.3% and 8.1% in each gender, respectively. The mean loss of bone was about twice as great in women as in men. In women, significant differences (p less than 0.01) were found in these variables after the seventh decade compared with the preceding age group. However, true bone density (W/CV) stayed almost unchanged regardless of age, being about 2.0 in men and about 1.9 in women. Osteoporosis could be primarily a manifestation of normal aging, including the postmenopausal estrogen deficiency in women, regardless of gender or race.