Obesity potentially protects against systemic bone loss in patients with rheumatoid arthritis treated with tumour necrosis factor inhibitors.

Objectives: We aimed to investigate how systemic bone metabolism was affected after 1 year of treatment with tumour necrosis factor (TNF) inhibitors in rheumatoid arthritis (RA) patients.

Methods: A total of 29 seropositive RA patients not treated for osteoporosis were enrolled and TNF inhibitors were administered for a year. Bone mineral density (BMD) at the lumbar spine, femur neck, and total hip was measured at baseline and 12 months after anti-TNF treatment. Blood samples were collected at baseline and 6 and 12 months after anti-TNF treatment and osteoclasts were cultured on bone slices. Weight was the strongest factor influencing systemic bone loss. Patients were categorised into two groups: obese (body mass index (BMI) ≥25 kg/m2) and non-obese (BMI <25 kg/m2).

Results: All patients showed decreased BMD at all sites. The obese group showed relatively little change in BMD, although the non-obese group showed significant decreases in BMD at all sites after 1 year of treatment with TNF inhibitors. Resorption pits created by osteoclasts decreased at 6 months and increased at 12 months in the non-obese group, while the obese group presented with steadily decreasing sizes of resorption pits at all-time points. Levels of receptor activator of nuclear factor kappa B ligand were significantly decreased at 12 months compared to baseline in the obese group, while they were increased in the non-obese group.

Conclusions: One year of treatment with TNF inhibitors failed to halt systemic bone loss in RA patients, but obesity may have protective effects against bone loss.