Abstract and Introduction
Abstract
Context: The relationship of visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) with bone mineral density (BMD) is not well established.
Objective: To examine the associations of VAT and SAT with total body BMD in a large, nationally representative population with a wide range of adiposity.
Methods: We analyzed 10 641 subjects aged 20 to 59 years in National Health and Nutrition Examination Survey 2011–2018 who had undergone total body BMD and had VAT and SAT measured by dual-energy X-ray absorptiometry. Linear regression models were fitted while controlling for age, sex, race or ethnicity, smoking status, height, and lean mass index.
Results: In a fully adjusted model, each higher quartile of VAT was associated with an average of 0.22 lower T-score (95% CI, −0.26 to −0.17, P < 0.001), whereas SAT had a weak association with BMD but only in men (−0.10; 95% CI, −0.17 to −0.04, P = 0.002). However, the association of SAT to BMD in men was no longer significant after controlling for bioavailable sex hormones. In subgroup analysis, we also found differences in the relationship of VAT to BMD in Black and Asian subjects, but these differences were eliminated after accounting for racial and ethnic differences in VAT norms.
Conclusions: VAT has a negative association with BMD. Further research is needed to better understand the mechanism of action and, more generally, to develop strategies for optimizing bone health in obese subjects.
Introduction
Although obesity has generally been thought to be protective against osteoporosis, we recently demonstrated that higher fat mass index was associated with lower bone mineral density (BMD) among more than 10 000 subjects in the National Health and Nutrition Examination Survey (NHANES).[1] This observation could partly explain the higher risk of fracture at the ankle, humerus,[2,3] and possibly other fracture sites seen in subjects with obesity.
The cause of lower BMD is not clear, and it did not appear that sex hormones or fat distribution fully explained our observations. One possibility is that adipokines and cytokines released from adipose tissue negatively affect BMD. If true, we should expect differing associations between BMD and visceral adipose tissue (VAT) vs subcutaneous adipose tissue (SAT). VAT is adipose tissue located within the abdominal cavity and within mesenteric fat, whereas SAT lies outside the abdominal cavity. VAT is known to be a secretory organ and is associated with metabolic syndrome, diabetes, cardiovascular disease, and cancer.[4] Studies demonstrate that VAT releases high levels of proinflammatory cytokines, such as TNF-α and IL-6, which could increase bone resorption.[5] Simultaneously, it is believed that VAT releases less leptin, a hormone thought to stimulate proliferation and differentiation of osteoblasts.[6] Despite these theoretical effects, the effect of VAT on bone health remains unclear, with previous studies being relatively small and limited to younger age groups, specific diseases, or homogeneous populations.[7–11] Similarly, the effect of SAT is not clear due to conflicting findings in prior studies.[7,12]
Although VAT and SAT have traditionally been measured by computed tomography (CT) or magnetic resonance imaging (MRI), dual-energy X-ray absorptiometry (DXA) is able to quantify VAT and SAT and compares well with these modalities.[13] Thus, we sought to evaluate the associations between VAT, SAT, and total body BMD from NHANES 2011–2018.
J Endo Soc. 2023;7(4) © 2023 Endocrine Society
