Quantifying the Balance Between Total Bone Formation and Total Bone Resorption: An Index of Net Bone Formation

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Bone gain vs loss across the skeleton loss depends on the balance between total bone formation and total bone resorption.


The objective of the study was to determine whether resorption and formation markers can be combined to gauge net bone formation across the skeleton.


The study included a cohort followed up across menopause transition (Study of Women's Health Across the Nation).

Setting and Participants:

Community-dwelling women, 42–52 years old, premenopausal or early perimenopausal at baseline, participated in the study.


The study included the following measures: 1) bone balance index (BBI) created by estimating the relationship between resorption (urinary N-telopeptide) and formation (osteocalcin) markers when the total formation equals the total resorption in 685 women with stable bone mineral density (BMD) (>5 y before the final menstrual period [FMP]) and applying this relationship to measured bone turnover markers in 216 women beginning to lose bone (≤2 y from FMP); and 2) annualized percentage declines over the following 3–4 years in the lumbar spine (LS) and femoral neck (FN) BMD.


Adjusted for covariates, the BBI was greater (more favorable) in women with a greater body mass index (P = .03) and lower (less favorable) in women closer to the FMP (P = .007). Each SD decrement in BBI was associated with 0.27%/y faster LS BMD decline (P 0.04) and a 38% higher odds of faster-than-average loss of LS bone mass (P = .008, c-statistic 0.76). BBI was not associated with decline in FN BMD. Urinary N-telopeptide alone was not associated with either LS or FN BMD decline.


An index that quantifies net bone formation vs resorption can be created from bone turnover markers and may help identify individuals at high risk for LS bone loss.

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