Age-related changes in the biochemical properties of human cancellous bone collagen: relationship to bone strength

The metabolism of bone collagen has received little attention in relation to age-related loss of bone mass and strength. The aim of the present study was to analyze bone collagen content and metabolism in human bone with respect to age. The material consisted of iliac crest bone biopsies from 94 individuals: 46 women (ages 18-96, mean age 60.8 years) and 48 men (ages 23-92, mean age 59.5 years). Excluded from the study were all individuals with known osteoporotic lumbar vertebral fractures and renal, hepatic, or malignant diseases. Prior to collagen analysis the biopsies were scanned in a pQCT scanner for density assessment and then tested biomechanically. The results showed a decline in apparent bone density with age (P < 0.0001), a decline in maximum stress, Young's modulus, and energy absorption with age (P < 0.001). Concomittantly, there was an age-related decline in the intrinsic collagen content with age (P < 0.001). However, there were no biochemical modifications of the bone collagen during aging. There were no significant differences between women and men in the slopes of the regressions-curves. When multiple regression analyses were performed, only apparent bone density came out as a significant contributor in the correlation to biomechanical properties. Nevertheless, the decrease in bone collagen content with age might indicate an increase in the mineralization degree (probably due to decreased bone turnover) and thereby a change in material properties of bone. In conclusion, the present study has shown that loss of bone mass plays the major role in loss of bone strength. However, there is also a change in bone composition during normal aging, leading to a decrease in collagen content and an increase in the degree of mineralization. At this skeletal site, in a normal population there was no change in the biochemical properties of bone collagen.