Nonlinear dose-response relationship between dietary niacin intake and osteoporosis in U.S. adults over 50 years of age: a cross-sectional study of the 2007-2018 National Health and Nutrition Examination Survey (NHANES)

osteoporosis (OP) is prevalent among older adults, and nutritional factors significantly contribute to its development. Although some studies suggest niacin may influence bone health, the existing evidence remains inconclusive. This study investigates the dose-response relationship between dietary niacin intake and osteoporosis risk in US adults aged 50 years or older, using nationally representative data from the National Health and Nutrition Examination Survey (NHANES, 2007-2018). this cross-sectional study included 2308 adults aged ≥ 50 years from the NHANES. Dietary niacin intake was assessed using two non-consecutive 24-hour dietary recalls. Weighted multivariable logistic regression analyzed associations between niacin and OP, while restricted cubic spline (RCS) models evaluated potential nonlinear dose-response relationships. the baseline analysis revealed significantly lower dietary niacin intake levels among OP patients. Multivariable logistic regression demonstrated that, after adjusting for confounders, participants in the highest percentile of dietary niacin intake exhibited a significantly reduced OP risk compared to those in the lowest percentile (OR: 0.81, 95 % CI: 0.68-0.84, p = 0.03), with a significant dose-response trend (p for trend = 0.04). Using RCS modeling, this study is the first to identify a nonlinear dose-response relationship (inverted U-shaped curve, overall p < 0.05, nonlinear p < 0.05) between niacin intake and OP risk. Subgroup analyses further revealed sex-specific differences in the association (p for interaction = 0.027), suggesting that niacin's skeletal benefits may vary by biological sex. These findings provide novel insights into niacin's role in OP prevention and inform personalized dietary recommendations. this study, based on NHANES data (2007-2018), first reveals a nonlinear inverted U-shaped association between dietary niacin intake and osteoporosis risk in a US population aged ≥ 50 years, filling the research gap in dose-response characteristics among middle-aged and elderly populations. It proposes a bone-protective threshold for niacin intake (18.62-50 mg/d), providing potential evidence for revising current dietary guidelines. Furthermore, the study innovatively employs RCS models to identify gender-specific inflection points, and is the first to demonstrate the significant moderating effect of gender on the niacin-osteoporosis association. These findings establish a scientific foundation for personalized nutritional interventions.