TSH (Thyroid Stimulating Hormone)
TSH (thyroid stimulating hormone) is produced by the pituitary gland and acts as the primary regulator of thyroid function. It signals the thyroid to produce T4 and T3 hormones. TSH operates via a negative feedback loop: when thyroid hormone levels are low, TSH rises to stimulate more production, and when they're high, TSH decreases.
TSH is the first-line screening test for thyroid disorders. An elevated TSH typically indicates hypothyroidism (underactive thyroid), while a suppressed TSH suggests hyperthyroidism (overactive thyroid). Subclinical thyroid dysfunction — where TSH is abnormal but free T3/T4 remain in range — is common and often symptomatic.
The optimal TSH range is narrower than the standard lab reference range. Many endocrinologists and functional medicine practitioners consider 1.0–2.0 mIU/L as the functional optimal range, associated with the lowest symptom burden and best metabolic function.
What It Measures
TSH measures the pituitary gland's signaling to the thyroid. It reflects the brain's perception of whether thyroid hormone levels are adequate. TSH is inversely related to thyroid hormone levels.
Reference Ranges
| Status | Range (mIU/L) |
|---|---|
| Optimal | 1.0–2.0 mIU/L |
| Normal | 0.5–4.5 mIU/L |
| Borderline | 4.5–10.0 mIU/L (subclinical hypothyroidism) |
| Out of Range | > 10.0 mIU/L or < 0.1 mIU/L |
Optimal Ranges
| Group | Range | Unit | Source |
|---|---|---|---|
| Standard | 0.45–4.5 | mIU/L | Standard reference |
| Optimal (functional) | 1–2.5 | mIU/L | Functional range |
When Values Are High
Elevated TSH indicates the thyroid is underperforming (hypothyroidism). The pituitary produces more TSH to stimulate the thyroid. Symptoms: fatigue, weight gain, cold intolerance, hair loss, constipation.
When Values Are Low
Low TSH suggests the thyroid is overactive (hyperthyroidism) or excessive thyroid hormone supplementation. Symptoms: anxiety, weight loss, heat intolerance, tremor, rapid heart rate.
What To Do
Lifestyle
- •Ensure adequate iodine intake (iodized salt, seaweed)
- •Manage stress — cortisol impairs T4→T3 conversion
- •Avoid excessive cruciferous vegetables if iodine-deficient
- •Regular exercise supports thyroid function
Supplements
- •Selenium 200mcg/day supports thyroid peroxidase function
- •Zinc is required for T3 receptor binding
- •Iron deficiency impairs thyroid hormone synthesis
When to Retest
Retest 6–8 weeks after dose adjustment; always test Free T3 and Free T4 alongside
How GATOR Tracks This
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Related Biomarkers
This content is for informational purposes only and does not constitute medical advice. Reference ranges may vary by laboratory and individual factors. Consult a qualified healthcare provider for interpretation of your results and treatment decisions.
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