Circadian rhythm in type I collagen formation in postmenopausal women with and without osteopenia

A circadian rhythm in the serum concentration of the procollagen type I carboxyl-terminal propeptide (sPICP) has previously been demonstrated in premenopausal women. This study was performed to investigate the circadian rhythm in sPICP in healthy and osteopenic postmenopausal women. Blood samples were taken every third hour for 27 h from three groups of women: 12 early postmenopausal women (aged 55 +/- 2 years; mean +/- SD); 12 late postmenopausal women (aged 73 +/- 1 years); and 12 osteopenic but otherwise healthy late postmenopausal women (aged 73 +/- 1 years). A circadian rhythm in sPICP was found in all three groups, as shown by cosinor analysis (p = 0.000003-0.03). The circadian rhythm in sPICP was significantly different between the osteopenic group and the age-matched healthy group (p < 0.008). The amplitude of the circadian rhythm in sPICP was about twice as high in the osteopenic group, and the time of the maximum tended to be about 3 h later, as compared with the age-matched healthy group. The plasma concentration of osteocalcin, as measured by a recently developed two-site enzyme-linked immunosorbent assay, also showed a circadian rhythm in all three groups (p = 0.0001-0.05), with no significant differences between groups. In conclusion, we have found a significant circadian rhythm in sPICP in both early and late postmenopausal women. In osteopenic women the nightly peak in sPICP is larger and persists later into the night as compared with non-osteopenic women.