Hypothyroidism occurs when your thyroid gland does not produce enough thyroid hormones (T3 and T4), which control your metabolism, energy, body temperature, and mood. The most common cause is Hashimoto's thyroiditis, an autoimmune condition where the immune system attacks the thyroid. It affects about 5% of Americans, with many more undiagnosed because standard testing only checks TSH.
Most doctors only check TSH, which misses subclinical hypothyroidism and conversion issues. Request a complete thyroid panel:
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The TSH reference range (0.4-4.5 mIU/L) is wide and population-based — it includes many people who feel unwell. Research shows that most people feel best with TSH between 0.5-2.0 mIU/L. Additionally, some people have low normal T4 but poor T4-to-T3 conversion, meaning their cells are not getting the active hormone they need. If your TSH is "normal" but you still have symptoms, request free T3 and reverse T3 — these are often not ordered but tell a more complete story.
Hashimoto's thyroiditis is the most common cause of hypothyroidism in developed countries — it is an autoimmune condition where the immune system attacks the thyroid gland, eventually leading to reduced hormone production. Not everyone with Hashimoto's is hypothyroid, and not all hypothyroidism is Hashimoto's. Testing TPO and thyroglobulin antibodies distinguishes autoimmune from non-autoimmune hypothyroidism, which matters for treatment (particularly the potential role of dietary interventions and immunomodulation).
Some patients who remain symptomatic on T4-only therapy respond better to combination T4/T3 therapy (either synthetic liothyronine or desiccated thyroid extract). Studies suggest that a subset of patients have genetic polymorphisms in deiodinase enzymes that impair T4-to-T3 conversion. If your free T3 is in the low-normal range despite normal TSH and T4, this may be worth discussing with your endocrinologist. Tracking symptoms against labs over time in Vitalix gives you the objective data to support that conversation.
Levothyroxine absorption is significantly reduced by calcium supplements, iron supplements, dairy, coffee, and high-fiber foods when taken within 1-4 hours of the dose. This is why taking levothyroxine on an empty stomach (30-60 minutes before eating) or at bedtime (several hours after eating) is recommended. Individual variation in absorption is significant — tracking how food timing correlates with your TSH over multiple lab draws can reveal whether absorption issues are affecting your treatment.
Yes, but usually not as much as patients expect. The weight gain from hypothyroidism (typically 5-10 lbs) is largely due to water retention and reduced metabolic rate. Most patients on adequate thyroid replacement do not lose all the weight they gained before diagnosis, because hypothyroidism often co-occurs with insulin resistance and other metabolic issues that independently drive weight gain. Tracking weight alongside thyroid labs and other metabolic markers in Vitalix reveals the full picture.
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