Ecological analysis of the association between dietary factors and thyroid cancer incidence based on GBD 2021 data

ObjectiveTo examine the association between dietary factors and thyroid cancer incidence worldwide, with particular attention to differences across regions at different levels of socioeconomic development.MethodsData on thyroid cancer incidence and per capita intake of 15 dietary factors in 194 countries and territories from 1990 to 2021 were extracted from the Global Burden of Disease (GBD) 2021 database. At the dietary-factor level, collinearity diagnostics were first performed, and Bayesian generalized linear mixed models with a gamma distribution and log link function were fitted using the age-standardized incidence rate of thyroid cancer as the outcome to estimate posterior regression coefficients and rate ratios. At the dietary-pattern level, principal component analysis was used to derive dietary patterns, and standardized pattern scores were then included in analogous Bayesian models. Heterogeneity in the associations was further assessed by stratified analyses according to the Sociodemographic Index (SDI), sex, and age.ResultsFrom 1990 to 2021, the global age-standardized incidence rate of thyroid cancer increased and showed marked regional variation. Incidence remained consistently higher in females than in males, and the age-specific incidence rates increased with age. Analysis of dietary exposure indicated that intake of dietary fiber, legumes, and nuts increased globally, whereas trans fat intake generally declined. Intake patterns of sugar-sweetened beverages and animal-source foods showed pronounced SDI-related differences. At the individual dietary factor level, the Bayesian multilevel model identified 11 factors significantly associated with the age-standardized incidence rate of thyroid cancer. Intake of legumes, fruits, sugar-sweetened beverages, red meat, trans fats, and sodium was positively associated with thyroid cancer incidence, whereas intake of nuts, dietary fiber, processed meat, milk, and vegetables was negatively associated with thyroid cancer incidence. At the dietary-pattern level, scores for dietary pattern 1 (characterized by high loadings of red meat, processed meat, sugar-sweetened beverages, and milk) and dietary pattern 2 (characterized by high loadings of fruits, legumes, vegetables, and polyunsaturated fatty acids, accompanied by a moderate loading of sugar-sweetened beverages) were positively associated with the age-standardized incidence rate of thyroid cancer. In contrast, the score for dietary pattern 3 (characterized by high loadings of nuts and omega-3 fatty acids) was negatively associated with thyroid cancer incidence.ConclusionsThe global increase in thyroid cancer incidence was statistically associated with changes in dietary structure. This association was more pronounced in medium-development countries undergoing nutritional transition. Higher intake of sugar-sweetened beverages and red meat was associated with increased incidence, whereas higher intake of dietary components such as nuts and vegetables was associated with lower incidence.