Your Thyroid Thermostat
TSH is like the thermostat for your thyroid. Your pituitary gland releases TSH to tell your thyroid how much hormone to make. Here's the counterintuitive part: HIGH TSH means LOW thyroid function (your brain is yelling at a lazy thyroid to work harder). LOW TSH means HIGH thyroid function (your brain is telling an overactive thyroid to calm down).
What is TSH (Thyroid Stimulating Hormone)?
TSH is produced by the pituitary gland to control thyroid hormone production. It's the most sensitive test for thyroid dysfunction—it changes before thyroid hormones themselves become abnormal. Normal is roughly 0.4-4.0 mIU/L, though optimal is debated.
↑ What High TSH (Thyroid Stimulating Hormone) Means
Your pituitary is shouting at your thyroid to produce more hormone—but it's not responding adequately. This is hypothyroidism: you'll feel sluggish, cold, foggy, and may gain weight. Everything slows down.
Common symptoms:
Hypothyroidism: fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, depression, brain fog
↓ What Low TSH (Thyroid Stimulating Hormone) Means
Your pituitary is whispering because there's already too much thyroid hormone. This is hyperthyroidism: you'll feel wired, anxious, hot, and may lose weight. Everything speeds up.
Common symptoms:
Hyperthyroidism: weight loss, rapid heartbeat, anxiety, tremor, heat intolerance, insomnia, diarrhea
Why It Matters
When normal:
Most sensitive thyroid screening test
Detects dysfunction before symptoms worsen
Guides medication dosing
Risks if abnormal:
Untreated hypothyroidism: fatigue, weight gain, depression, high cholesterol, heart disease
Untreated hyperthyroidism: weight loss, anxiety, heart arrhythmias, bone loss
What Can Cause Abnormal Levels?
Hashimoto's Thyroiditis (if high)
80% likelyAutoimmune destruction of thyroid. Most common cause of hypothyroidism.
Graves' Disease (if low)
70% likelyAutoimmune stimulation of thyroid. Most common cause of hyperthyroidism.
Iodine Deficiency or Excess
Both can affect thyroid function.
Medications
Lithium, amiodarone, and others affect thyroid.
What You Can Do
Ensure adequate iodine (from iodized salt, seafood, dairy)
Impact: Supports thyroid function \u00B7 Timeline: Ongoing
Selenium: 200mcg daily (if borderline high TSH)
Impact: May reduce antibodies \u00B7 Timeline: 8-12 weeks
If lifestyle changes aren't enough:
If Hashimoto's: gluten-free trial (some evidence)
Impact: May reduce antibodies in sensitive individuals \u00B7 Timeline: 3-6 months
Optimize vitamin D (supports immune regulation)
Impact: May help autoimmune thyroiditis \u00B7 Timeline: 3-6 months
Recommended retest: 6-8 weeks after medication change, otherwise 6-12 months
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