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TSH - An Update to The Ranges
Dicken Weatherby, N.D. and Beth Ellen DiLuglio, MS, RDN, LDN
The question of what is a “high” or a “low” TSH has been debated for some time. This post presents evidence to support a change in the optimal range for TSH.
Thyroid-stimulating hormone (TSH) regulates thyroid hormone production through a complex feedback system involving the hypothalamus, the pituitary gland (where TSH is produced), and the thyroid gland itself.
An elevated TSH will stimulate the thyroid to produce more thyroid hormone, while a decreased level signals to the thyroid that no more hormone is needed.
The question of what is a “high” or a “low” TSH has been debated for some time. Concern that the current standard ranges are not identifying underlying thyroid dysfunction has been a tenet of Functional Blood Chemistry Analysis. Now many clinicians and professional organizations share that concern and call for an update to TSH ranges.
Thyroid dysfunction can have a broad range of consequences due to its essential role in vascular integrity, energy expenditure, and lipid and glucose metabolism. Manifestations of insufficient thyroid hormone can include insulin resistance, dyslipidemia, diastolic hypertension, and endothelial dysfunction.
In order to detect early trends toward thyroid dysfunction, levels of TSH outside the optimal range should be monitored and addressed before metabolic imbalance and overt pathology occur.
Initial Assessment of Thyroid Function
Measuring TSH is the best initial screening tool available for assessing thyroid status.
Elevated TSH indicates hypothyroidism, which can be clinical (accompanied by reduced serum thyroid hormone) or subclinical (normal levels of thyroid hormone). Though iodine deficiency causes hypothyroidism, most clinical hypothyroidism is caused by Hashimoto thyroiditis or “Hashimoto’s,” an autoimmune disorder.
Common symptoms of hypothyroidism include elevated cholesterol, cognitive changes, dry skin, constipation, cold intolerance, weight gain, and fatigue.
A decreased level of TSH indicates hyperthyroidism, most commonly associated with Graves’ disease. Symptoms of hyperthyroidism include nervousness, irritability, palpitations, heat intolerance, and weight loss.
Additional biomarkers to be evaluated include free and total T4 and T3, and anti-thyroid antibodies. Iodine status should also be evaluated.
Optimal levels of TSH
Standard lab values for TSH range from 0.4 mU/L to 4.5 mU/L in adults.
However, research demonstrates that levels between 2.5-4.5 mU/L were significantly associated with obesity, high triglycerides, risk of metabolic syndrome, and increased prevalence of anti-thyroid antibodies.
TSH levels below 1 mU/L have been associated with compromised bone density and increased risk of vertebral fracture.
Considering that approximately 95% of healthy individuals maintain a TSH below 2.5 mU/L, and thyroid dysfunction is lowest with a TSH of 1-1.9 mU/L,  a range of 1-2 mU/L is considered optimal for TSH. Individuals that fall above or below this optimal range can be further assessed and monitored for thyroid dysfunction before it progresses into metabolic dysfunction.
Want to dive deeper into this topic?
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