Risk factors for low bone mineral density in premenopausal women with endometriosis in the national health and nutrition examination survey (NHANES)

Abstract

Women with endometriosis have a higher preponderance of demographic and lifestyle risk factors associated with low postmenopausal bone mineral density (BMD). However, it is unclear whether endometriosis confers an additional risk of low BMD or fracture after menopause. Further, data on risk factors for low premenopausal BMD are limited. We aimed to compare premenopausal BMD and the risk of major osteoporotic fracture (in women ≥40 years old) between women with and without endometriosis, accounting for known postmenopausal risk factors. We also aimed to identify risk factors for low premenopausal BMD in women with and without endometriosis. A cross-sectional analysis was conducted in 2770 premenopausal women aged 20-54 years who participated in either NHANES 2005-06, 2007-08 and 2009-10 cycles. Data on endometriosis (available in 2005-06 only) and potential risk factors for low BMD were collected through in person interviews and physical exams by trained medical professionals. Circulating 25-OH D levels were measured in blood samples collected during the exam. Femoral neck BMD was measured via dual-energy X-ray absorptiometry (DXA) densitometers. The 10-year risk of major osteoporotic fracture was estimated through the validated FRAX® score. NHANES survey analysis procedures were used to account for the complex sampling design. Least-squares mean femoral neck BMD and FRAX® scores were estimated by linear regression in women with endometriosis (N=43) matched by age and race to women without endometriosis (N=344). Odds ratios for risk of low BMD (lowest decile) were calculated by logistic regression in all women (N=2770). Accounting for age and race, femoral neck BMD in women with endometriosis (mean = 0.826 g/cm2) was lower, but not significantly different from BMD in women without endometriosis (mean BMD = 0.846 g/cm2) (p, 0.47). Among women ≥40 years old, the 10-year risk of fracture was low in women with endometriosis (risk = 2.9%) and women without (risk=2.7%) (p, 0.41). Older age (≥40 years), white race, prior fracture; diagnosis of osteoporosis, and BMI<18.5 kg/m2 were independently associated with low BMD in premenopausal women (C-statistic = 0.78). These factors were more common in women with compared to women without endometriosis, but the discrimination of the model in women with endometriosis was lower (C-statistic = 0.52). Risk factors identified for low BMD in premenopausal women were consistent with predictors of osteoporosis in postmenopausal women, although the sample size limited the ability to distinguish differences in women with and without endometriosis. Longitudinal studies are needed to determine whether the long-term fracture rate in women with endometriosis is significantly different than women without endometriosis.