The potential causal relationship between fat mass in different body areas and low back pain: Findings from NHANES...

The purpose of this study is to investigate and discuss the potential relationship between fat distribution in different body regions and low back pain (LBP). We used 2 research methods to study the impact of fat distribution on LBP. First, we conducted a cross-sectional study using National Health and Nutrition Examination Survey data to examine the relationship between fat levels in the trunk and lower limbs and LBP. Second, we employed a two-sample Mendelian randomization approach to investigate the causal relationship between trunk fat, lower limb fat, and LBP. In the cross-sectional study, the results of multivariable logistic regression analysis showed that for every unit increase in trunk fat mass (FM) (kg), the risk of LBP increased by 2.8% (odds ratios, OR = 1.028, 95% confidence intervals [CI] [1.021, 1.034], P < .00001). Similarly, there was a positive correlation between right leg FM, left leg FM, and LBP (fully adjusted model: OR = 1.075, 95% CI [1.053, 1.097], P < .00001; OR = 1.076, 95% CI [1.053, 1.099], P < .00001). Mendelian randomization analysis indicated that an increase in trunk FM had a detrimental effect on LBP (OR = 1.296, 95% CI [1.207-1.392], P = 9.86 × 10-13), while an increase in left lower limb FM had a protective effect on LBP (OR = 0.672, 95% CI [0.604-0.748], P = 2.61 × 10-13), and an increase in right lower limb FM also had a protective effect on LBP (OR = 0.655, 95% CI [0.590-0.728], P = 3.32 × 10-15). The study revealed a positive causal relationship between trunk FM and LBP. However, the causal relationship between FM in the lower extremities and LBP remains controversial. Nonetheless, investigating lower extremity FM as a potential protective factor in depth is a direction worth focusing on in the future.