Factors that should be considered when studying the effect of dietary
iodine in the development of
thyroid cancer include pathological criteria, diagnostic techniques, screening programs,
radioactive fallout, and standard of medical care in the studied population. In most surveys,
papillary carcinoma forms the largest group of thyroid
malignancies, both before and after
iodine prophylaxis where an increase in the papillary:follicular
carcinoma ratio is also noted.
Undifferentiated carcinomas decrease after
salt prophylaxis. In Salta, Argentina, the increasing incidence of clinically significant
papillary thyroid cancer and the decrease of
undifferentiated carcinoma after
iodine prophylaxis are probably due to better access to health centers and consequent earlier detection of differentiated precursor
tumors. Autoimmune focal and diffuse or Hashimoto's
thyroiditis are linked to dietary
iodine. Pathological studies made in different regions indicate that these types of
thyroiditis occur more frequently in areas of
iodine sufficiency than in areas of
iodine deficiency, and increase after
iodine prophylaxis both in non-goitrous and
iodine-deficient areas like Salta, Argentina. An increase of
lymphocytic thyroiditis could be linked to an increased incidence of primary thyroid
lymphoma, and
thyroiditis is more commonly associated with
papillary carcinoma than with other types of thyroid follicular or C-cell derived
carcinomas regardless of
iodine intake.