Physical activity reduces the risk of osteoporosis in patients with arthritis: A dual-cohort prospective study and mechanistic exploration.

BACKGROUND: Osteoporosis is a major complication in patients with arthritis, yet the long-term protective effect of physical activity (PA) and its underlying mechanisms are not fully understood.

METHODS: This study utilized two large aging cohorts, the U.S. Health and Retirement Study (HRS) and the English Longitudinal Study of Ageing (ELSA). All exposures and outcomes, including PA and physician-diagnosed arthritis and osteoporosis, were based on self-reported data. Cross-sectional analyses assessed the association between PA and arthritis-osteoporosis comorbidity. Longitudinal Cox models examined the effect of baseline PA on new-onset osteoporosis in patients with arthritis. Subgroup, E-value, and mediation analyses were performed to explore effect heterogeneity, robustness, and the mediating role of depression. An exploratory reverse analysis assessed the association of PA with new-onset arthritis in osteoporosis patients.

RESULTS: Among 20,175 HRS and 10,525 ELSA participants in the cross-sectional analysis, and 8032 HRS and 2984 patients with arthritis in the prospective analysis, PA was associated with lower comorbidity prevalence (HRS: OR = 0.78; ELSA: OR = 0.69). In longitudinal analyses, active PA was independently associated with reduced osteoporosis risk (HRS: HR = 0.86; ELSA: HR = 0.70) in patients with arthritis. The effect was more pronounced in younger patients and those with heart disease or depression. In HRS, depression significantly mediated 36.55% of the protective effect, whereas this mediation pathway was non-significant in ELSA. No significant association was found between PA and new-onset arthritis in osteoporosis patients.

CONCLUSION: Regular physical activity was associated with a lower risk of osteoporosis in patients with arthritis; the association may be partly explained by improvements in depressive symptoms. Promoting PA should be integral to clinical management.