The incidence of differentiated
thyroid cancer has been increasing in the last decades all over the world. Such a steady growth cannot be entirely attributable to more intensive
thyroid nodule screening and more sensitive diagnostic procedures. Several environmental factors have changed with sufficient rapidity in the same time frame and may represent credible candidates for this increase. They include modified
iodine intake, lifestyle-associated risk factors, exposure to various toxic compounds,
pollutants and
xenobiotics,
nutritional deficiencies, eating habits and comorbidities. Foremost, nutritional patterns have gained high interest as possible promoters and modifiable risk factors for
thyroid cancer in recent years. The aim of this narrative review is to focus on the relationship between
thyroid cancer and nutritional factors, dietary habits and
obesity. Low
iodine intake has been associated to increased risk of
thyroid cancer, favoring the development of more aggressive histotypes. Moreover, correction of
iodine deficiency can shift
thyroid cancer subtypes toward less aggressive forms, without affecting the overall risk for
cancer. Actually, evidence regarding the association between
selenium and
vitamin D deficiency and
thyroid cancer is very limited, despite their well-known anti-
cancer potentials, and the clinical usefulness of their supplementation is still uncertain in this setting. Albeit the relationship between single foods and
thyroid cancer is difficult to examine, fish and
iodine-rich foods, vegetables, and fruits might exert protective effects on
thyroid cancer risk. Conversely, no clear association has been found for other foods to date. Lastly, a clear association between
obesity and the risk of
thyroid cancer, with more aggressive behavior, seems to emerge from most studies, likely involving variations in thyroid function and chronic
inflammation mediated by
cytokines,
insulin,
leptin and adiponectins. Although no definite association between dietary factors and
thyroid cancer has been firmly established so far, some nutritional patterns, together with excessive weight, seem to play a relevant role in
thyroid cancer carcinogenesis as well as in its severity and aggressiveness. These effects may play an additive role to the well-established one exerted by
environmental carcinogens, such as
pollutants and radiation exposure.