Osteoporosis: pathogenesis and risk factors

Bone-derived serum enzymes and bone density in perimenopausal Caucasian women

Serum levels of bone-origin alkaline phosphatase and of tartrate-resistant acid phosphatase were measured in Caucasian women aged 41-69 years who had volunteered for bone densitometry. Bone alkaline phosphatase and tartrate-resistant acid phosphatase were inversely correlated with vertebral bone density and with femoral neck bone density. Bone alkaline phosphatase and acid phosphatase were also significantly correlated, consistent with the concept of 'coupling' between osteoblast and osteoclast activity.

Sex differences in the acquisition of total bone mineral mass peak assessed through dual-energy X-ray absorptiometry

Dual energy X-ray absorptiometry evaluation of total body bone mineral content (TBBM), total bone mineral density (TBMD), and regional bone mineral content (BMC) (head, trunk, arms, and legs) was carried out in order to assess sex differences of bone in 120 women and 121 men aged 15-29 years. Subjects from both sexes were divided into 5-year groups (15 through 19, 20 through 24, and 25 through 29 years old, respectively). Significantly higher values for TBBM, TBMD, and regional BMC were observed in males compared with females in the 20 to 24 and 25 to 29-year-old groups (P less than 0.001), but not in the group aged 15-19. After adjusting TBBM for lean body mass (LBM), we observed significantly lower values of TBBM/LBM in the males compared with females in all the age groups. A positive and significant correlation was observed between TBBM and age in the males of all the groups (r = 0.624, P less than 0.001), but not in the females. These data suggest that total bone mass peak acquisition takes place earlier in women than in men, leading to more reduced bone mass value, which in turn may be an osteoporosis predisposing factor.

Role of oestrogen in the development of osteoporosis

The evidence now strongly supports a central role for oestrogen in the maintenance of the normal female skeleton. Loss of endogenous oestrogen leads to a period of accelerated bone loss which can be prevented with appropriate oestrogen replacement. The route of administration is not important provided adequate dosages are prescribed. Oestrogens may exert their actions by a direct steroid receptor mechanism or via local and/or systemic factors such as cytokines, prostaglandins or calcitonin. As the requirement for osteoporosis prevention grows, it is essential that the extent of the involvement oestrogen has in skeletal homeostasis is fully recognized.

Habitual dietary calcium intake and cortical bone loss in perimenopausal women: a longitudinal study

During an 8-year follow-up study, the effect of habitual dietary calcium intake on cortical bone loss in 154 healthy perimenopausal women was examined. Dietary calcium intake, determined by the cross-check dietary history method, and cortical bone mineral content of the radius were measured annually. Habitual dietary calcium intake was calculated as the mean of the estimated daily dietary calcium intake during the follow-up period. The women were classified according to their habitual calcium intake: those with an intake below 800 mg/day (n = 28), between 800 and 1350 mg/day (n = 95), and above 1350 mg/day (n = 31). The results show a continuous significant loss of cortical bone in all groups, amounting yearly to 1.3 +/- 0.25, 1.5 +/- 0.10, and 1.9 +/- 0.23% (mean +/- SE) for the groups with a low, medium, and high habitual calcium intake, respectively (P less than 0.01). The differences among the three groups did not reach statistical significance (P = 0.11). Body mass index was found to be positively correlated with the negative changes in cortical bone mineral density (r = 0.32, P less than 0.01), even after adjustments had been made for confounding factors. It is concluded that a habitual calcium intake exceeding 800 mg/day (the current Recommended Daily Allowance for adults) is ineffective in preventing cortical bone loss during early menopause. Body mass index is of major importance for the perimenopausal bone loss.