Table 1.

Summary of the key genetic, environmental, and existential factors associated with Hashimoto’s thyroiditis

Genetic factors

Major histocompatibility genes (HLA class I and II)

Immunoregulatory genes (e.g. CTLA4, PD1, CD40)

Thyroid-specific genes (TG)

Genes associated with thyroid peroxidase antibody synthesis (e.g. TPO, BACH2)

Environmental factors

Iodine intake—possible U-shaped relationship

Smoking—protective but increased risk when stopped

Alcohol—protective

Selenium—evidence equivocal

Vitamin D—evidence equivocal

Infections—evidence equivocal except for congenital rubella and hepatitis C; may operate through childhood exposure (the hygiene hypothesis) or gut microbiota

Therapies which modulate the immune system; lithium; irradiation

Existential factors

Female sex

Pregnancy

Age

Down’s syndrome

Associated disease—prolactinoma, allergic rhinitis, subacute thyroiditis (all equivocal)