Higher systemic immune-inflammation index associates with vertebral marrow proton density fat fraction in...

The systemic immune-inflammation index (SII) may influence bone homeostasis through inflammatory modulation. Although bone marrow adipocytes regulate bone metabolism via adipokine secretion, their interaction with SII remains unexplored. We investigated the SII-marrow adiposity relationship in postmenopausal women.

This retrospective study included 187 postmenopausal women. Lumbar spine MRI using chemical shift encoding generated proton density fat fraction (PDFF) maps, with bone mineral density (BMD) measured by dual x-ray absorptiometry. The relationship between SII and marrow PDFF was evaluated through multivariable-adjusted linear regression, smooth curve fittings, and threshold analysis.

The results revealed a negative correlation between marrow PDFF values and BMD (r = - 0.438, P < 0.001). After accounting for age, time since menopause, body mass index, physical activity, C-reactive protein, interleukin (IL)-1β, IL-6, tumor necrosis factor-α, and BMD in the regression analysis, each unit increase in SII was found to be inked to an increase of 0.247 (β = 0.247; 95% confidence interval [CI], 0.212 to 0.281; P <0.001) in PDFF. After converting SII to a categorical variable (quartiles), participants in the highest SII quartile had a 16.8% higher vertebral marrow PDFF than those in the lowest SII quartile (β = 16.753, 95% CI: 11.036-18.522, P <0.001). Furthermore, a curvilinear relationship and threshold effect were also identified. Turning point was identified at the SII value of 441 on the adjusted smooth curve.

SII levels were positively associated with marrow adiposity in postmenopausal women.