Influence of long-term postmenopausal hormone-replacement therapy on estimated structural bone strength: A study in discordant monozygotic twins

Abstract

Although postmenopausal hormone-replacement therapy (HRT) is known to prevent fractures, knowledge on the influence of long-term HRT on bone strength and its determinants other than areal bone mineral density is scarce. This study used a genetically controlled design with 24 monozygotic female twin pairs aged 54 to 72 years in which one cotwin was using HRT (mean duration 8 years) and the other had never used HRT. Estimated bone strength, cross-sectional area, volumetric bone mineral density, bone mineral mass, and cross-sectional density and mass distributions were assessed in the tibial shaft, distal tibia, and distal radius with peripheral computed tomography (pQCT). In the tibial shaft, HRT users had 9% [95% confidence interval (CI) 3%-15%] higher estimated bending strength than their nonusing cotwins. Larger cortical area and higher cortical bone mineral density accounted for this difference. The cortex was larger in the HRT users in the endocortical region. In the distal tibia, estimated compressive strength was 24% (95% CI 9%-40%) higher and in the distal radius 26% (95% CI 11%-41%) higher in the HRT users than in their nonusing cotwins owing to higher volumetric bone mineral density. No difference between users and nonusers was observed in total bone cross-sectional area in any measured bone site. The added mineral mass in the HRT users was distributed evenly within and between bone sites. In postmenopausal women, long-term HRT preserves estimated bone strength systemically by preventing bone mineral loss similarly in body weight-loaded and non-weightloaded bone. ß

The strength of weight‐bearing bones is similar in amenorrheic and eumenorrheic elite long‐distance runners

“…36 At the same time, both the radius and tibia had expanded. These findings are similar to that previously suggested by Mikkola et al 37 in that the effect of estrogen is systemic with the tibia and radius being affected similarly. This effect also has some similarity to the decline in trabecular BMD 38 and increase in bone size 39 during pregnancy.…”

“…The lower bone strength indicators in bones of the trunk but not the radius of amenorrheic athletes is not entirely explained by reduced loading, but rather suggests that the bone response to amenorrhea is site‐specific. While the strength of weight‐bearing bones in the EA and AA are similar, the enlargement of the endocortical area, similar to that shown by Mikkola et al cannot be reversed by loading. We speculate that this can only be normalized by a return to a normal menstrual cycle.…”

“…This pregnancy‐induced loss of BMD can be recovered during lactation when the child is weaned and if the underlying cause is similar, the expansion of the endocortical circumference in the amenorrheic athletes could most likely be recovered by normalization of the menstrual cycle. In a study of monozygotic twins, hormone replacement therapy (HRT) was associated with larger cortical bone areas and smaller endocortical areas . It is not known, however, if this would be effective in amenorrheic athletes as the duration of HRT in the twins study was on average 8 years.…”

“…In a study of monozygotic twins, hormone replacement therapy (HRT) was associated with larger cortical bone areas and smaller endocortical areas. 37 It is not known, however, if this would be effective in amenorrheic athletes as the duration of HRT in the twins study was on average 8 years. Although regular exercise was associated with a smaller endocortical area in monozygotic twins, 35 it is unlikely that normalization of the endocortical circumference in amenorrheic athletes can be realized by increased loading, as both the unloaded radius and the loaded tibia exhibit this increase in endocortical circumference.…”

Comparison of plain vertebral X‐ray and dual‐energy X‐ray absorptiometry for the identification of older women for fracture prevention in primary care

“…It is noteworthy that a past history of at least 6 months of HRT or OCP use was associated with a higher BMD but did not differentiate women with vertebral fractures from those without fractures. This is consistent with hormone therapy having an impact on bone mineral mass and bone strength possibly without impacting the microarchitecture, the integrity of which has been implicated in vertebral fracture …”