Mitochondria-DNA copy-number in osteoporosis and osteoarthritis among middle-aged women - A population-based cohort study

Background: Mitochondrial DNA copy number (mtDNA-CN) is associated with aging. A relationship between mtDNA-CN and degenerative disorders, e.g. osteoarthritis (OA) and osteoporosis (OP), has been suggested. We aimed to investigate the relationship of mtDNA-CN and incident OA and OP.

Materials and methods: MtDNA-CN was studied in relationship to incident OA and OP in a population-based cohort study of 6916 middle-aged women (52-63 years). Totally 2521 women with sufficient quality of mtDNA were analyzed. After exclusions, 1978 women remained in the study population. Four different endpoints obtained from the National Patient register were studied: 1) OA, 2) OP 3) OA surgery, and 4) OP fracture. In the multivariate model adjustments were made for potential OA and OP risk factors.

Results: Women with low mtDNA-CN were older and had more activity at work. 125 women (6.32%) were affected by incident OP and 254 women (12.84%) had an OP fracture. Incident OA affected 451 women (22.80%) and 175 women (8.85%) had OA surgery. There were no associations between mtDNA-CN and incident risk of OA (Hazard ratio ​= ​1.00, 95% confidence interval 0.83-1.20), OA surgery (0.79, 0.58-1.07), OP (0.89, 0.62-1.27), or OP fracture (1.00, 0.78-1.29). However, incident OP was significantly associated with T-score (bone density), smoking, diabetes mellitus, and chronic obstructive bronchitis (COPD). OA was associated with body mass index and COPD.

Conclusions: The present study suggests that mtDNA-CN, reflecting mitochondrial dysfunction, is not a major predictor for incident OA or OP. However, due to the limited study size minor associations cannot be excluded.