Epidemiological association between metabolic health obesity phenotype and chronic low back pain: a cross-sectional analysis based on the NHANES database

Abstract

BACKGROUND: Currently, whether and how the metabolically healthy obesity phenotype influences the risk and pathological progression of chronic low back pain compared to metabolically unhealthy obese individuals remain unclear. Research is urgently needed to clarify their association and potential mechanisms. OBJECTIVE: To investigate the epidemiological association between the metabolically healthy obesity phenotype and chronic low back pain. METHODS: Using data from the US National Health and Nutrition Examination Survey (NHANES) 1999-2004 and 2009-2010 (n=4,956), a retrospective cross-sectional study was conducted. Obesity was defined by body mass index and waist circumference according to WHO standards, and metabolic phenotype was stratified using core metabolic syndrome indicators (fasting glucose, lipid profile, blood pressure, etc.), establishing metabolically healthy obesity and metabolically unhealthy obesity classification. Multivariable-adjusted logistic regression models and restricted cubic spline curves were used to systematically evaluate the nonlinear dose-response relationship between metabolic health obesity phenotype and chronic low back pain risk. Multivariable-adjusted models were established to analyze chronic low back pain risk, and subgroup analysis, threshold effect analysis, and multiple sensitivity analyses were used to verify model robustness. RESULTS AND CONCLUSION: (1) Metabolically unhealthy obesity significantly increased the risk of chronic low back pain [BMI standard: OR (95%CI)=1.44 (1.11, 1.85), P=0.0070; waist circumference standard: OR (95%CI)=1.57 (1.25, 1.97), P=0.0003]. Smoking [OR (95%CI)=1.44 (1.24, 1.67), P<0.0001] and arthritis [OR (95%CI)=2.44 (2.06, 2.88), P<0.0001] significantly amplified the risk effect of metabolically healthy obesity on chronic low back pain. BMI ≥39.73 kg/m² and waist circumference ≥125 cm were risk thresholds for chronic low back pain in metabolically unhealthy individuals. Low education level, low income, and widowed/divorced or separated status increased the risk of chronic low back pain. In the total population and metabolically unhealthy participants, there was a linear relationship between BMI and chronic low back pain (P<0.05). In metabolically healthy participants, the dose-response relationship between BMI and chronic low back pain was approximately linear (P>0.05); in the total population, metabolically healthy and metabolically unhealthy participants, the dose-response relationship between waist circumference and chronic low back pain was approximately linear (P>0.05). (2) Based on NHANES cross-sectional analysis, metabolically unhealthy obesity was significantly and positively independently associated with chronic low back pain, while metabolically healthy obesity had a weaker and non-statistically significant association, indicating that metabolic health status is an important factor influencing chronic low back pain in obese individuals. The model constructed from international research provides a key theoretical reference for exploring racial heterogeneity and localized mechanisms (such as Asian-specific metabolic thresholds) in the Chinese population. The results warn that China should pay attention to the risk of low back pain in metabolically healthy obese individuals, promote optimized clinical classification intervention strategies (such as avoiding excessive weight loss), and prospectively prevent the public health burden of obesity-related musculoskeletal diseases.

1. Introduction

Chronic low back pain is not only the most common type of musculoskeletal disorder but also a leading cause of disability globally. According to the Global Burden of Disease Study 2021, 619 million people worldwide are affected by chronic low back pain, with projections indicating a 36.4% increase by 2050 [1]. This condition consumes substantial healthcare resources [2-3].

Obesity, defined as a body mass index (BMI) ≥30 kg/m², has become a severe global health issue, particularly in the United States where the age-adjusted prevalence is 42.4% [4]. Evidence suggests that obesity leads to numerous complications, including diabetes, cardiovascular disease, hypertension, cancer, and musculoskeletal pain, and has been established as an independent risk factor for chronic low back pain [5-9]. Studies have highlighted that obesity increases the risk of lower trunk musculoskeletal pain [10-11]. Previous research indicates that obesity coexists with metabolic abnormalities, and obesity-related metabolic disorders can mediate the incidence of obesity-related diseases [12]. Moreover, the pathological mechanisms of chronic low back pain exhibit significant metabolic interactions with obesity [13]. Smith et al. [14] showed that if health is defined as the absence of metabolic syndrome, approximately 50% of obese patients can be considered metabolically healthy; however, when health is defined as having no metabolic syndrome components and normal insulin sensitivity assessed by insulin resistance indices, only about 5% of obese patients meet the criteria. Cohort studies have also shown that metabolically healthy obese individuals have a lower risk of cardiovascular events compared to metabolically unhealthy obese individuals, but the relationship with chronic low back pain remains unclear.