Does hyperthyroidism or hypothyroidism increase Follicle-Stimulating Hormone (FSH) levels?

Effects of Thyroid Dysfunction on FSH Levels

Hyperthyroidism increases FSH levels, while hypothyroidism generally does not significantly affect FSH levels. 1, 2

Hyperthyroidism and FSH

• In hyperthyroidism, FSH secretion is significantly increased, particularly in men 1
• Studies show that patients with Graves' disease (hyperthyroidism) demonstrate elevated gonadotropin levels, including FSH 1
• The increased FSH levels occur without changes to the pulsatile characteristics (frequency, peak shape) of FSH secretion 1
• This elevation may be due to altered feedback mechanisms in the hypothalamic-pituitary-gonadal axis during thyroid hormone excess

Hypothyroidism and FSH

• In hypothyroidism, FSH levels are not consistently or significantly affected 2
• A 2016 study found that although average serum FSH was slightly lower in hypothyroid patients compared to after achieving euthyroidism, this difference was statistically insignificant 2
• In male patients with primary hypothyroidism, FSH may be elevated in children (associated with testicular enlargement without virilization), but this pattern is not consistently observed in adults 3
• After thyroid hormone replacement therapy in hypothyroid patients, FSH levels tend to normalize 4

Clinical Implications

• When evaluating reproductive hormone profiles in patients with thyroid dysfunction, clinicians should consider:

  • The differential effects of hyperthyroidism versus hypothyroidism on FSH levels
  • The potential for thyroid dysfunction to affect other reproductive hormones (LH, estradiol, testosterone, prolactin)
  • The reversibility of these hormonal changes with appropriate thyroid treatment

• Thyroid function should be evaluated in patients with unexplained changes in reproductive hormones, as thyroid disorders can significantly impact the hypothalamic-pituitary-gonadal axis 5

Diagnostic Considerations

• When interpreting FSH levels in patients with suspected thyroid dysfunction:
  • Always measure TSH, free T4, and free T3 simultaneously 5
  • Consider the pattern of other reproductive hormones (LH, estradiol, testosterone)
  • Remember that thyroid dysfunction can alter sex hormone-binding globulin (SHBG) concentrations, which affects interpretation of total hormone levels 3

Treatment Implications

• Normalizing thyroid function through appropriate treatment (antithyroid medications for hyperthyroidism or thyroid hormone replacement for hypothyroidism) generally restores normal FSH levels and reproductive function 4
• In patients with fertility concerns and thyroid dysfunction, optimizing thyroid function should be a priority, as treating thyroid disorders may positively impact reproductive function 5

Common Pitfalls

• Failing to check thyroid function in patients with unexplained reproductive hormone abnormalities
• Attributing reproductive symptoms solely to FSH abnormalities without considering the broader impact of thyroid dysfunction on multiple reproductive hormones
• Not recognizing that thyroid hormone replacement can normalize reproductive hormone profiles in hypothyroid patients