Total lymphocyte count and femoral bone mineral density in postmenopausal women

In vitro studies showed that several cytokines produced by the immune system can play a relevant role in modulating bone turnover, thus affecting the health of bone tissue. Our aim was to evaluate the association between total lymphocyte count (TLC) and femoral bone mineral density (BMD) in a sample of postmenopausal women. We studied 114 out of 124 consecutive, caucasian, home-dwelling, apparently healthy postmenopausal women referred for osteodensitometry by general practitioners. Femoral BMD was measured by dual-energy X-ray absorptiometry at five sites. A significant positive correlation (p < 0.001) was observed between TLC and BMD (T score) measured the five sites: total proximal femur (r = 0.45), trochanter (r = 0.43), intertrochanteric region (r = 0.38), femoral neck (r = 0.49), and Ward's triangle (r = 0.42). With a linear multiple regression model, TLC adjusted for age, weight, height, body mass index, and erythrocyte sedimentation rate showed a significant association with femoral BMD assessed at each of the five sites. The R-2 values ranged from 0.33 with BMD measured at Ward's triangle to 0.51 with BMD measured at the trochanter. The significance of the association between TLC and BMD ranged from P < 0.001 with BMD measured at the femoral neck to P < 0.05 with BMD measured at the intertrochanteric area. The results were similar when BMD was expressed as either a Z score (in the 110 of the 114 women aged 84 years or younger) or as absolute values. Our data show a positive association between TLC and femoral BMD in a sample of apparently healthy, postmenopausal women, supporting the view of a close connection between the immune system and bone tissue.