Background: Shorter estrogen exposure from puberty onset to peak bone mass (PBM) attainment may explain how late menarche is a risk factor for osteoporosis. The influence of menarcheal age (MENA) on PBM, cortical and trabecular microstructure was studied in 124 healthy women aged 20.4±0.6 (SD) yrs.

Methods: At distal radius, areal bone mineral density (aBMD) was measured by DXA, and volumetric BMD and microstructure by high resolution pQCT including: total (Dtot), cortical (Dcort), and trabecular (Dtrab) volumetric BMD and fraction (BV/TV), trabecular number (TbN), thickness (TbTh) and spacing (TbSp), cortical thickness (CTh) and cross-sectional area (CSA).

Results: MENA median was 12.9 yrs. Mean aBMD T-score of the whole cohort was slightly positive. aBMD was inversely correlated to MENA for total radius (R=-0.21, p=0.018), diaphysis (R=-0.18, p=0.043) and metaphysis (R=-0.19, p=0.031). Subjects with MENA > median (LATER: 14.0±0.7 (±SD) yrs) had lower aBMD than those with MENA < median (EARLIER: 12.1±0.7 yrs) in total radius (p=0.026), diaphysis (p=0.042) and metaphysis (p=0.046). LATER vs. EARLIER displayed lower Dtot (315±54 vs. 341±56 mgHA/cm3, p=0.010), Dcort (874±49 vs. 901±44 mgHA/cm3, p=0.003) and CTh (774±170 vs. 849±191 µm, p=0.023). CTh was inversely related to CSA (R=-0.46, p<0.001). In LATER reduced CTh was associated with 5% increased CSA.

Conclusion: In healthy young adult women a 1.9 yr difference in mean menarcheal age was associated with lower radial aBMD T-score, lower CTh without reduced CSA, a finding compatible with less endocortical accrual. It may explain how late menarche is a risk factor for forearm osteoporosis.