Dietary Inflammatory Index and Thyroid Disease: A Large Prospective Cohort Study

Thyroid disorders are highly prevalent endocrine diseases. While systemic inflammation is known to contribute to thyroid dysfunction, the impact of dietary inflammatory potential remains inadequately characterized. We investigated the associations between the Dietary Inflammatory Index, energy-adjusted Dietary Inflammatory Index, and incident thyroid diseases in a large prospective cohort. We analyzed 210,839 UK Biobank participants (2008–2012). Dietary Inflammatory Index and energy-adjusted Dietary Inflammatory Index scores were derived from 24-hour dietary recalls. Cox proportional hazards models estimated hazard ratios. Restricted cubic splines characterized dose–response relationships, and mediation analyses assessed whether inflammatory and metabolic markers mediated these associations. Higher Dietary Inflammatory Index and energy-adjusted Dietary Inflammatory Index scores were significantly associated with increased risks of overall thyroid disease, hypothyroidism, and hyperthyroidism. Each 1-point increment in energy-adjusted Dietary Inflammatory Index was associated with a 4% higher risk of overall thyroid disease (hazard ratio: 1.04; 95% confidence interval: 1.02–1.06) and a 10% higher risk of hyperthyroidism (hazard ratio: 1.10; 95% confidence interval: 1.05–1.15). Dose–response analyses showed linear associations for hypothyroidism and overall thyroid disease, and a J-shaped pattern for hyperthyroidism. Platelet count, neutrophil count, C-reactive protein, and insulin-like growth factor-1 partially mediated these associations. Pro-inflammatory dietary patterns are associated with elevated risks of thyroid disease, partly mediated by systemic inflammatory and metabolic pathways. These findings identify dietary inflammation as a modifiable risk factor for thyroid health.