Risk Factors Associated with Hypothyroidism
Three major risk factors for hypothyroidism are: (1) female sex and advanced age, (2) autoimmune disease or family history of thyroid disorders, and (3) prior thyroid interventions including surgery, radioactive iodine treatment, or head/neck radiation.
Demographic Risk Factors
Female sex is a primary risk factor, with women developing hypothyroidism at significantly higher rates than men—the prevalence of subclinical hypothyroidism reaches up to 20% in women over age 60 compared to much lower rates in men 1
Advanced age substantially increases risk, as the prevalence of hypothyroidism increases progressively with aging, affecting a higher proportion of elderly individuals 2, 1
Race influences susceptibility, with Black individuals having approximately one-third the rate of hypothyroidism compared to white populations 1
Autoimmune and Genetic Risk Factors
Hashimoto's thyroiditis (autoimmune thyroid disease) is the leading cause of primary hypothyroidism in iodine-sufficient areas like the United States, accounting for up to 85% of cases 1, 3
Family history of thyroid disease confers genetic predisposition, with having a first-degree relative with hypothyroidism significantly increasing individual risk 1, 3
Coexisting autoimmune conditions elevate risk, particularly type 1 diabetes mellitus, which is associated with increased likelihood of developing autoimmune thyroid disease 1
Treatment-Related and Iatrogenic Risk Factors
Previous thyroid surgery or radioactive iodine treatment commonly results in hypothyroidism, as these interventions directly damage or remove thyroid tissue 1, 4
Head and neck radiation therapy can damage thyroid tissue and lead to subsequent hypothyroidism 1
Certain medications increase risk, including lithium carbonate, amiodarone (due to high iodine content), and immune checkpoint inhibitors used in cancer treatment 1, 3, 4
Environmental and Nutritional Risk Factors
Iodine deficiency remains an important global cause, though less common in areas with routine salt iodination 1, 4
Excessive iodine intake from sources like CT contrast or iodine-containing medications can transiently affect thyroid function 5
Special Population Risk Factors
Pregnancy in the setting of underlying autoimmune thyroid disease increases risk, as hypothyroidism may be associated with adverse pregnancy outcomes including preeclampsia, low birth weight, and neurodevelopmental effects in offspring 5, 1
Postpartum women represent a higher-risk group for developing thyroid dysfunction 2
Patients with Down syndrome have elevated risk for thyroid dysfunction, though evaluating symptoms can be challenging due to overlapping clinical features 2
Common Clinical Pitfalls
High levels of radiation exposure (>20 mGy) should trigger consideration of thyroid screening, as this represents a significant risk factor 2
Inadequate thyroid medication dosing affects approximately 20% of patients already taking thyroid medications, leading to persistent subclinical hypothyroidism 1
Pituitary or hypothalamic disorders can cause secondary (central) hypothyroidism, though this is less common than primary thyroid gland failure 4, 6