SAT-531 Low 25-OH-Vitamin D Levels in Women Observed before Initiating Osteoporosis Therapy

Introduction: Vitamin D sufficiency is integral for bone health in postmenopausal women at risk for fracture. This study examines the prevalence of low 25-OH-vitamin D (25OHD) levels in women in the two years before they initiated osteoporosis therapy. The possible contributions of race, body mass index (BMI), and race-specific thresholds to classify vitamin D status were investigated. Methods: A retrospective study was performed using data from older women aged 45-89y who initiated oral bisphosphonate therapy in 2010-2013 and had a 25OHD level within the prior 2 years. The primary outcome was low vitamin D, defined as a serum 25OHD level <20 ng/ml (standard threshold). Patient data included race/ethnicity and BMI classified as underweight (<18.5), normal (18.5-24.9), overweight (25-29.9), and obese (≥30 kg/m2). Chi-square test was used to compare subgroups. Log binomial regression was used to examine the independent relationships between race, BMI and low 25OHD level, represented as relative risk (RR) and 95% confidence interval (CI). Since previous studies found that black women may have a lower vitamin D requirement, we also performed a sensitivity analysis using a race-specific threshold of 25OHD <15 ng/ml for black women. Results: Among 18,519 women (70% white, 3% black, 10% Hispanic, 15% Asian, and 2% other/unknown), 22% had a low 25OHD level. The prevalence varied by race/ethnicity and was lowest for white (19%) compared to black (45%), Hispanic (33%), and Asian (22%) women. Using the race-specific threshold, the prevalence in blacks fell to 34%. BMI status also varied by race; for white women, 31% and 21% were overweight and obese, compared to 33% and 27% of blacks, 38% and 29% of Hispanics, and 25%, and 7% of Asians. Overall, higher BMI was associated with a greater prevalence of low 25OHD (18%, 22%, and 29% for normal, overweight, and obese BMI, respectively). This trend was seen when stratifying by race (white: 16%, 19%, 26%; Hispanic: 28%, 33%, 41%; and Asian: 19%, 25%, 30%) except for black race (44%, 46%, 45%, or 36%, 30%, 35% using the race-specific threshold). Adjusting for age and BMI, black (RR 2.2, CI 2.0-2.5 or RR 1.7, CI 1.5-1.9 using the race-specific threshold), Hispanic (RR 1.7, CI 1.6-1.8) and Asian (RR 1.2, CI 1.1-1.3) race/ethnicity were associated with an increased risk of low 25OHD compared to white women. Conclusion: Prior to initiation of osteoporosis therapy, the prevalence of low 25OHD is high (about 1 in 5). Although black and Hispanic women comprise a minority of women starting bisphosphonate therapy, they appeared to be at highest risk for low levels, even when a lower threshold is applied. Obesity also increases the likelihood of having a low 25OHD level, except for women of black race. These findings may inform osteoporosis care optimization, including increased efforts to screen and replete vitamin D levels, especially in non-white or Hispanic women and those with high BMI.