Risk Factors

Gender:1 the incidence of thyroid disorders is reported to be higher in women than in men.

Age:1 the risk of developing thyroid disease is elevated in individuals 50 years of age, and above.

Stress:2 it has been observed that major stress may contribute to disturbances in thyroid function. However, the majority of studies examining this effect have been conducted in psychiatric patients, and the results may therefore be influenced by the study population.

Family history:1 patients with a family history of thyroid disease are at an increased risk of developing an autoimmune thyroid condition. Similarly, a family history of autoimmune disease also increases the risk of thyroid disorders, albeit to a lesser extent.

Thyroid surgery / medical treatment:3 patients who have undergone any form of thyroid surgery or radioactive iodine treatment to remove part or all of the thyroid, may become hypothyroid as a result. Certain medical treatments and drugs can increase the risk of developing an underactive thyroid. These include interferon β-1b, interleukin-4, immunosuppressants, antiretrovirals, monoclonal antibodies (Campath-1H), bone marrow transplant, lithium and amiodarone, among others. In addition, treatment of hepatitis C with interferon 2α has been associated with increased risk of thyroid dysfunction, which usually resolved upon discontinuation of treatment.4 Recent exposure to a surgical antiseptic that includes iodine (such as Povidone) can increase the risk of temporary thyroiditis, hypothyroidism or hyperthyroidism.

Radiation Exposure:3 exposure of the neck area to radiation, such as in the treatment of head or neck cancer, or accidental environmental exposure, increases the risk of autoimmune thyroid disease and thyroid cancer. Medical tests that use iodine-based contrast enhancing dyes can slightly increase the risk of developing a temporary thyroiditis, hypothyroidism or hyperthyroidism. 

Pregnancy:5 the risk of developing thyroid disorders increases during pregnancy. Increased levels of human chorionic gonadotropin (hCG) and estrogen are thought to be responsible for alterations in the levels of thyroid hormones.

Smoking:1 thiocyanate in cigarettes adversely affects the thyroid. Smokers, therefore, have an increased risk of developing autoimmune thyroid diseases, and smoking can exacerbate existing symptoms of thyroid disease.

Diet:5 insufficient dietary iodine increases the risk of hypothyroidism (most common in developing countries). In contrast, dietary supplementation with iodine-containing herbal remedies among individuals with sufficient dietary iodine intake can increase the risk of autoimmune thyroid disease. In susceptible people (usually those with underlying thyroid autoantibodies), foods containing goitrogens (chemicals that can promote goitre) can induce hypothyroidism when eaten raw and in large quantities. Some foods that are high in goitrogens include cabbage, brussel sprouts, broccoli, turnips, rutabagas, kohlrabi, radishes, cauliflower, African cassava, millet, soy and kale.

  1. Manji N, Carr-Smith JD, Boelaert K, et al. Influences of age, gender, smoking, and family history on autoimmune thyroid disease phenotype. J Clin Endocrinol Metab. 2006;91(12):4873–4880. 
  2. Sarne D. Thyroid Disease manager 2010;Chapter 5.
  3. Mayo Clinic. Hypothyroidism. 2010.
  4. Kee KM, Lee CM, Wang JH, et al. Thyroid dysfunction in patients with chronic hepatitis C receiving a combined therapy of interferon and ribavirin: incidence, associated factors and prognosis. J Gastroenterol Hepatol. 2006;21(1 Pt 2):319-326. 
  5. National Institute of Diabetes and Digestive and Kidney Diseases. Pregnancy and Thyroid disease. 2008.
  6. Brown RS. Thyroid Disease manager. 2009;Chapter 15b.

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