In this 15-year follow-up study, we found that the estimated rate of bone loss at the femoral neck (FN) for women aged 45-68 was linear at a rate of 1.67% per year, but quadratic for lumbar spine (LS) at a rate of 3.12% initially, and slowing down with age. We also confirmed the protective role of HRT, increasing weight, and lean mass in long-term bone loss.
Introduction: The objective was to describe the natural history of bone loss and explore the role of environmental factors in postmenopausal women over a 15-year period.
Methods: Bone mineral density (BMD) at the FN and the LS were measured in postmenopausal women from the Chingford Study. Height, weight, HRT status, and calcium/vitamin D supplement were assessed at each visit. Osteoarthritis of hip and spine was assessed by X-ray at baseline and at year 8.
Results: A total of 955 postmenopausal women with an average age of 54.7 at baseline were included. Both FN and LS BMD decreased significantly with age (p<0.0001). The decline was larger in the LS (-3.12% per year), which showed a quadratic relationship, than in the FN (-1.67% per year) with a linear relationship. The rate of bone loss was reduced by one third annually for the FN and LS respectively in current HRT users. Change in weight was positively associated with both DeltaFN and DeltaLS BMD (beta=0.16% and 0.09% change in DeltaFN and DeltaLS BMD per kilogramme change in weight respectively, p<0.0001 for both sites). Spine OA and progression were positively associated with DeltaLS BMD (beta=1.22% change in DeltaLS BMD per grade in spine OA and 0.45% change in DeltaLS BMD for patients who progressed, p<0.0001 for spine OA and p=0.002 for spine OA progression). Spine OA (beta=0.54% change in DeltaFN BMD per grade, p<0.0001), but not progression, and hip OA were positively associated with DeltaFN BMD. Furthermore, both age and body weight at baseline were positively associated with both DeltaFN and DeltaLS BMD (beta=0.02-0.04% change in DeltaFN and DeltaLS BMD per year increase in age at baseline and 0.004-0.007% change in DeltaFN and DeltaLS BMD per kilogramme increase in weight at baseline, all p<0.0001).
Conclusion: This large population-based longitudinal study demonstrated that the decline of BMD over 15 years is linear with age for the FN, but quadratic for the LS. The study confirmed the protective role of HRT, increased weight and lean mass in long-term bone loss.