Whether iodized salt consumption increases thyroid cancer incidence

BACKGROUND AND OBJECTIVES This study aimed to explore the correlation between population-based iodine intake from iodized salt (iodine-IS) and thyroid cancer (TC) incidence. METHODS AND STUDY DESIGN The TC incidence data were collected from the annual reports issued by China's National Central Cancer Registry. The iodine- IS data were extracted from the National Iodized Salt Surveys and National IDD Surveys (NIDDs). The time lag effect of iodine-IS on TC incidence was examined by using a polynomial distributed lag (PDL) model. RESULTS Iodine-IS consumption peaked in 1999, declined to approximately 60% of 1999 in 2018, but remained close to 142.2 μg/person/day. After 2000, TC incidence increased notably on an annual basis. Iodine-IS and the age-standardized rate adjusted to the world population of TC incidence were significantly negatively correlated (p<0.05). The PDL model revealed that iodine-IS had a significant 6-year time lag effect on TC incidence (p<0.05). CONCLUSIONS Iodine nutrition, as indicated by iodine-IS, exhibited a steady decline. The populationbased iodine-IS was adequate, however, TC incidence continued increasing. Although the 6-year cumulative effect of iodine-IS was considered, a negative correlation between iodine-IS and TC incidence was observed. Iodine- IS may not be a major risk factor for TC because universal salt iodization is maintaining adequate iodine nutrition in the population. The increasing TC incidence may reduce public willingness to consume iodized salt.