Bone formation rate in older normal women: concurrent assessment with bone histomorphometry, calcium kinetics, and...

In 12 younger (age, 30-41 yr) and 11 older (age, 55-73 yr) normal women we assessed bone formation rate using multiple methods. Bone formation (mean +/- SE) was higher in the older women than in the younger women, based on measurements of serum bone Gla-protein (1.67 +/- 0.07 vs. 1.14 +/- 0.10 nmol/L; P less than 0.01), serum bone-specific alkaline phosphatase activity (388 +/- 42 vs. 223 +/- 22 nanokatal/L, P less than 0.01), and bone formation rate by histomorphometry of iliac biopsy (31.1 +/- 4.9% vs. 15.1 +/- 2.7%/yr; P less than 0.01), but was similar in the two groups when accretion rates were assessed by calcium kinetics (5.9 +/- 1.0 vs. 7.5 +/- 1.2; P = NS). This latter discrepancy may have been caused by several age-related factors, especially reduced mineralization of completed osteons, and by not correcting for the decrease in total skeletal calcium in the older group. Our data call into question the traditional belief that bone turnover decreases in older women.