Hormones
TSH
What This Marker Tells Us
Produced by your pituitary gland to regulate thyroid hormone production, acting as your body's thermostat for metabolic function and providing the most sensitive screening test for thyroid disorders.
Why It Matters
Typically the first and most important marker for detecting thyroid dysfunction because it amplifies small changes in thyroid hormone levels. When thyroid hormones drop even slightly, TSH rises significantly to stimulate more production, making it an early warning system for hypothyroidism. Conversely, when thyroid hormones are excessive, TSH suppresses to near zero. Hypothyroidism (high TSH) causes fatigue, weight gain, cold intolerance, depression, constipation, hair loss, and cognitive sluggishness. Subclinical hypothyroidism (elevated TSH with normal T4) often causes similar symptoms and increases cardiovascular risk. Hyperthyroidism (low TSH) causes anxiety, weight loss, rapid heartbeat, heat intolerance, and tremors. Optimal TSH supports balanced energy, healthy metabolism, temperature regulation, and mood stability. Many functional medicine practitioners target TSH below 2.5 mIU/L for optimal function, even though lab ranges extend to 4.5-5.0 mIU/L.
How to Interpret Your Trends
Optimal TSH is generally 0.5-2.5 mIU/L, though lab reference ranges often extend to 4.5-5.0 mIU/L. TSH below 0.5 mIU/L suggests hyperthyroidism or excessive thyroid medication, requiring evaluation to prevent bone loss and cardiac issues. TSH of 2.5-4.5 mIU/L may be subclinical hypothyroidism, especially with symptoms; many people feel better with TSH below 2.5 mIU/L. TSH above 4.5 mIU/L indicates hypothyroidism requiring treatment. Rising TSH trends over time, even within reference range, suggest declining thyroid function. TSH varies slightly throughout the day and is highest in the morning, so consistency in testing time helps track trends.
What Influences This Marker
TSH rises with primary hypothyroidism (Hashimoto's thyroiditis, iodine deficiency, thyroid surgery), inadequate thyroid medication dosing, aging, stress, illness, and certain medications (lithium, amiodarone). It decreases with hyperthyroidism (Graves' disease, toxic nodules), excessive thyroid medication, pituitary disorders, severe illness, and biotin supplementation (which can interfere with testing). Pregnancy, significant weight loss, high-intensity exercise, and caloric restriction can affect TSH. Subclinical hypothyroidism is strongly associated with metabolic syndrome and cardiovascular risk.
How Your Team Uses It
Your coach implements nutrition and lifestyle strategies supporting thyroid health: adequate iodine through seafood and iodized salt, selenium-rich foods like Brazil nuts, stress management practices, sleep optimization, and appropriate training intensity that doesn't suppress thyroid function.
Related Signals We Also Review
Free T4, free T3, total T4, thyroid antibodies (TPO, thyroglobulin), ferritin, vitamin D, and comprehensive metabolic health markers.