Associations between visceral adipose index, lipid accumulation products, and thyroid function parameters in U.S. Adults: analysis of NHANES data.

Background: Obesity, particularly visceral adiposity, is linked to altered thyroid function; the underlying mechanisms, however, remain unclear. This study examines the associations between the visceral adiposity index (VAI), lipid accumulation product (LAP), and thyroid function in U.S. adults.

Methods: This cross-sectional study used National Health and Nutrition Examination Survey (NHANES) data (2007-2012), including 3,170 participants after exclusions. Thyroid function parameters, VAI, and LAP were analyzed. Covariates included demographics, lifestyle, clinical factors, multiple linear regression, and restricted cubic splines, while generalized additive models were employed to assess linear and nonlinear relationships.

Results: VAI and LAP were significantly associated with thyroid function parameters. VAI positively correlated with total triiodothyronine [β = 0.79, 95% confidence interval (CI) = 0.37 to 1.21, P < 0.001] and antithyroglobulin antibodies (β = 1.81, 95% CI = 0.19 to 3.43, P = 0.028) after adjusting for confounders. LAP demonstrated significant positive associations with total triiodothyronine, thyroid-stimulating hormone (TSH), and thyroid sensitivity indices (e.g., TSH index and thyroxine resistance index) but correlated negatively with free thyroxine. Nonlinear relationships were identified, with higher VAI linked to rapid increases in total triiodothyronine and antithyroglobulin antibodies, plateauing at specific thresholds. Elevated LAP was associated with increased thyroid peroxidase antibodies, suggesting a link with thyroid autoimmunity.

Conclusions: VAI and LAP are strongly associated with thyroid dysfunction, with implications for thyroid sensitivity and autoimmunity. These findings underscore the importance of addressing visceral adiposity and metabolic dysregulation to mitigate thyroid-related disorders. Future studies are warranted to explore causal mechanisms and intervention strategies.