How do stress, weight loss, illness, and thyroid problems affect Follicle-Stimulating Hormone (FSH) levels in men?

FSH Sensitivity to Stress, Weight Loss, Illness, and Thyroid Problems in Men

The statement that FSH in men is "very sensitive" to stress, weight loss, illness, and thyroid problems is misleading and requires significant clarification—while these factors can affect the hypothalamic-pituitary-gonadal axis, FSH itself shows variable and often modest responses, with thyroid dysfunction having the most documented direct effects.

Thyroid Dysfunction and FSH

Thyroid problems have the most clearly established relationship with FSH alterations in men:

• Primary hypothyroidism is associated with elevated FSH levels in male children (causing testicular enlargement without virilization), though this pattern is less consistent in adult men 1
• Hyperthyroidism increases FSH secretion in men, with one study showing significantly elevated FSH levels compared to controls, though the pulsatile characteristics (frequency, peak shape) remain unchanged 2
• Thyroid hormone directly affects sex hormone-binding globulin (SHBG) concentrations, which can indirectly influence the gonadotropin feedback loop 1
• Correction of thyroid dysfunction reverses these FSH changes, demonstrating that thyroid-related FSH alterations are functional rather than representing permanent testicular damage 1

Stress and Energy Deficiency Effects

The evidence for stress and energy deficiency affecting FSH comes primarily from studies in athletes and military personnel, but the effects are indirect:

• Chronic energy deficiency and excessive endurance exercise in male athletes can cause hypogonadotropic hypogonadism (low FSH and LH), not elevated FSH 3
• Military studies tracking male recruits through basic training demonstrate significant effects on testosterone and cortisol from combined stresses (intensified training, sleep loss, energy deficiency), though FSH changes are not specifically highlighted 3
• The mechanism involves suppression of GnRH pulsatility, which reduces both LH and FSH secretion, with FSH being affected to a lesser extent than LH since reduced GnRH pulsatility actually favors FSH secretion 3

Weight Loss and Metabolic Stress

Weight loss and metabolic stress affect FSH indirectly through hypothalamic-pituitary suppression:

• Functional hypothalamic amenorrhea (FHA) in women—caused by stress, vigorous exercise, weight loss, and psychological disorders—results from reduced GnRH pulse frequency, leading to decreased LH and sometimes FSH levels 3
• While these studies focus on women, the underlying mechanism of hypothalamic suppression applies to men, though the clinical presentation differs 3
• Energy-deficient male swimmers and rowers show changes in bioenergetic hormones (free T3, insulin-like growth factor-1) and stress hormones (cortisol) during intensified training, though FSH measurements are not consistently reported 3

Acute Illness Effects

Acute illness affects TSH more dramatically than FSH, and the evidence for FSH sensitivity to illness is limited:

• Serum TSH is frequently suppressed during phases of acute illness, demonstrating high sensitivity to non-thyroidal illness 3
• No comparable evidence exists demonstrating that FSH shows similar acute sensitivity to illness in men
• The provided evidence does not support the claim that FSH is "very sensitive" to general illness states

Critical Caveats and Clinical Implications

Several important limitations must be recognized:

• FSH levels show substantial day-to-day variability (up to 50% of mean values), with up to 40% variation in serial measurements performed at the same time of day, making single FSH values unreliable 3
• Drugs and substances (iodine, dopamine, glucocorticoids, octreotide, bexarotene) can interfere with TSH but have less documented effects on FSH 3
• The primary determinant of FSH levels is testicular function itself—elevated FSH typically reflects primary testicular dysfunction rather than being a sensitive marker of external stressors 4, 5
• FSH levels are negatively correlated with spermatogonia number, meaning elevated FSH indicates decreased sperm production, not increased sensitivity to stress 4

Practical Clinical Approach

When evaluating FSH in the context of potential stressors:

• Always check thyroid function (TSH, free T4) when FSH is abnormal, as thyroid dysfunction is the most reversible cause of FSH alterations 3, 1
• Obtain at least two FSH measurements separated by several weeks to account for natural variability before making clinical decisions 3
• Assess for energy deficiency, excessive exercise, and psychological stress in men with low-normal or suppressed FSH (hypogonadotropic pattern) 3
• Elevated FSH (>7.6 IU/L) typically indicates primary testicular dysfunction rather than being a sensitive marker of stress or illness 4, 5
• Measure LH and testosterone concurrently to distinguish primary testicular failure (elevated FSH and LH, low testosterone) from hypothalamic-pituitary suppression (low FSH, LH, and testosterone) 3, 4