Cross-sectional evaluation of bone metabolism in men

There are relatively few data concerning age-related changes of bone turnov er in men. The aim of the study was to evaluate age-related changes of the levels of serum and urinary biochemical markers of bone metabolism in a lar ge cohort of 934 men aged 19-85 years and to investigate their association with bone mineral density (BMD). Bone formation was evaluated using serum l evels of osteocalcin (OC), bone alkaline phosphatase (BAP), and N-terminal extension propeptide of type I collagen (PINP). Bone resorption was evaluat ed by measurement of urinary excretion of beta -isomerized C-terminal telop eptide of collagen type I (beta -CTX) of free deoxypyridinoline (fDpyr) and total Dpyr (tDPyr) and of the serum level of beta -CTX. Levels of biochemi cal bone markers were very high in young men and decreased rapidly until th e age of 40 years and then more slowly until 60 years of age. After the age of 60 years, markers of bone formation remained stable while resorption ma rkers showed a moderate and variable increase with aging. Serum and urinary beta -CTX levels were elevated only in about 5% of elderly men. The age-re lated increase of urinary excretion of tDpyr and of its free and peptide-bo und fractions was related to the presence of elevated levels in a subgroup of about 15% of elderly men. Before 60 years of age, levels of biochemical bone markers were not correlated with BMD, whereas after 60 years of age, t hey were correlated negatively with BMD. After adjustment for age and body weight, BMD in men with the highest levels of biochemical bone markers (i.e ., in the upper quartile) was 1.8-12.5% (i.e., 0.25-0.89 SD) lower than in men with levels of biochemical bone markers in the lowest quartile. In conc lusion, bone turnover in men is high in young adults and decreases to reach a nadir at 55-60 years of age. After the age of 60 years, bone resorption markers-but not bone formation markers-increase in some men and are associa ted with lower BMD, suggesting that this imbalance is responsible for incre asing bone loss in elderly men.