Can waist circumference be a predictor of bone mineral density independent of BMI in middle-aged adults?

BACKGROUND: Obesity and osteoporosis are major public health issues globally. The prevalence of these two diseases prompts the need to better understand the relationship between them. Previous studies, however, have yielded controversial findings on this issue. Therefore, our aim in this study was to evaluate the independent association between waist circumference (WC), as a marker of obesity, and the bone mineral density (BMD) of the lumbar spine among middle-aged adults using data from the National Health and Nutrition Examination Survey (NHANES). METHODS: Our analysis was based on NHANES data from 2011 to 2018, including 5084 adults, 40–59 years of age. A weighted multiple linear regression analysis was used to evaluate the association between WC and lumbar BMD, with smooth curve fitting performed for non-linearities. RESULTS: After adjusting for BMI and other potential confounders, WC was negatively associated with lumbar BMD in men (β = −2.8, 95% CI: −4.0 to −1.6) and premenopausal women (β = −2.6, 95% CI: −4.1 to −1.1). On subgroup analysis stratified by BMI, this negative association was more significant in men with a BMI ≥30 kg/m(2) (β = −4.1, 95% CI: −6.3 to −2.0) and in pre- and postmenopausal women with a BMI <25 kg/m(2) (premenopausal women: β= −5.7, 95% CI: −9.4 to−2.0; postmenopausal women: β=−5.6, 95% CI: −9.7 to −1.6). We further identified an inverted U-shaped relationship among premenopausal women, with a point of inflection at WC of 80 cm. CONCLUSIONS: Our study found an inverse relationship between WC and lumbar BMD in middle-aged men with BMI ≥30 kg/m(2), and women with BMI <25 kg/m(2).