Forearm bone mineral content does not decline with age in premenopausal women

Forearm densitometry was performed on 77 normal premenopausal women aged 22-59 years. Bone mineral content (BMC) (arbitrary units) was converted into true forearm mineral content (FMC) (mg/cm) by measuring and ashing a sample radius and ulna. FMC was divided by width to yield surface density (mg/cm2) and divided by cross-sectional area to yield forearm mineral density (FMD) (mg/ml). The coefficient of variation of FMC was 12.3%, which was reduced to 10.1% after correction for width and 10.9% after correction for area. FMC was significantly related to height, bone width, and bone area but not to weight. The correlation with height was lost when FMC was corrected for bone width or bone area. None of the measured or derived bone variables was significantly related to age. Neither total bone mass nor bone density declines with age in premenopausal women. A comparison of normal and osteoporotic women will be required to establish whether bone width or bone area is the best referent for forearm mineral content.