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.