Hypothyroidism
Hypothyroidism is an endocrine disorder where the thyroid gland does not produce enough thyroid hormone. Because thyroid hormones regulate basal metabolic rate, a deficiency causes systemic slowing of bodily functions.
Clinical Presentation (Symptoms)
Symptoms of hypothyroidism are notoriously non-specific, meaning they overlap with dozens of other conditions (such as depression, aging, and chronic fatigue). Diagnosis cannot be made on symptoms alone and requires blood testing.
- Metabolic: Unexplained weight gain, profound fatigue, cold intolerance.
- Neurological: Brain fog, depression, impaired memory.
- Dermatological: Dry skin, brittle nails, thinning hair (particularly the outer third of the eyebrows).
- Gastrointestinal: Severe constipation.
Diagnostic Blood Work (The TSH Feedback Loop)
The primary screening tool is the Thyroid Stimulating Hormone (TSH) test.
The pituitary gland in the brain constantly monitors thyroid hormone levels in the blood. If levels are low, the pituitary gland secretes more TSH to "yell" at the thyroid gland to work harder. Therefore, a high TSH indicates hypothyroidism.
Standard Reference Ranges
- Normal TSH: 0.4 to 4.0 mIU/L
- Subclinical Hypothyroidism: TSH 4.0 to 10.0 mIU/L (with normal Free T4)
- Overt Hypothyroidism: TSH > 10.0 mIU/L (or elevated TSH with low Free T4)
Etiology (Causes)
In the developed world, the most common cause of hypothyroidism is Hashimoto's Thyroiditis, an autoimmune condition where the body's immune system attacks and destroys the thyroid gland. This is confirmed by testing for TPO (Thyroid Peroxidase) antibodies.
Treatment Protocol
Treatment is straightforward and highly effective: synthetic thyroid hormone replacement, most commonly Levothyroxine (Synthroid).
- Dosing: Must be taken on an empty stomach, ideally 30-60 minutes before breakfast, or at bedtime (at least 3 hours after the last meal).
- Interactions: Iron, calcium supplements, and certain antacids severely impair the absorption of Levothyroxine and must be taken at least 4 hours apart.
- Monitoring: TSH levels are usually rechecked 6 to 8 weeks after starting or changing a dose, as the hormone takes a long time to reach steady-state levels in the blood.