We measured bone osteocalcin concentrations in EDTA extracts from iliac crest cortical bone specimens obtained postmortem from 63 men and 71 women (age range 19-90 years), and serum osteocalcin levels in healthy blood donors, 49 men and 49 women (age range 21-65 years). Bone and serum osteocalcin concentrations were higher in men than in women, and an age-related decline was observed in both sexes. In women, however, a temporary increase in serum (P less than 0.05) osteocalcin was seen in the sixth decade. This study shows sex- and age-related changes in bone osteocalcin consistent with changes in serum osteocalcin, confirming that serum measurement of osteocalcin reflects bone levels. As osteocalcin reflects osteoblastic activity and thus bone formation, the overall decline in bone and serum osteocalcin in men and women, and the increase in serum osteocalcin in the sixth decade in women, indicate that aging is associated with a decrease in bone formation and turnover and that osteoblastic activity and bone turnover are stimulated at the menopause.

The relation between bone mineralization and osteocalcin content was investigated in iliac crest cortical bone obtained at necropsy in young females and in two groups of elderly women with and without osteoarthritis of the hands evaluated by X-ray. Using density fractionation technique, the bone was separated into fractions of increasing density from 1.72 to 2.30 g/ml. The mineralization profile revealed a significant shift to higher densities in the osteoarthritis cases compared with young adults (P less than 0.005) and age-sex-matched controls (P less than 0.001). The ash, calcium, and phosphorus content of the bone increased with increasing density of the fractions whereas collagen content, measured as hydroxyproline, decreased. The osteocalcin concentration of each fraction was determined in the supernatants obtained after EDTA-extraction in the presence of protease inhibitors. In the young control and osteoarthritis group, the osteocalcin content in the lowest density fractions was higher compared with the older non-osteoarthritic group. Osteocalcin content of the high density fractions, representing highly mineralized osteons, was the same in the three groups studied. These findings support the hypothesis that quality differences in bone may explain the inverse relationship between osteoarthritis and osteoporosis.