The thyroid gland produces thyroxine (T4) and triiodothyronine (T3), hormones that regulate metabolic rate, protein synthesis, body temperature, and energy balance across every tissue in the body. Thyroid dysfunction becomes increasingly common with age, and subclinical hypothyroidism, where thyroid-stimulating hormone is elevated but T3 and T4 remain within normal range, is particularly prevalent in adults over 50 and particularly in women.
The Symptoms That Suggest Assessment
- Unexplained weight gain or difficulty losing weight despite appropriate diet and exercise
- Persistent fatigue disproportionate to sleep quality and duration
- Cold intolerance, feeling cold when others do not
- Slow resting heart rate and reduced exercise capacity
- Constipation, dry skin, and hair thinning or loss
- Low mood and cognitive slowing
The Testing Nuance
TSH testing alone, the standard screening test, misses a proportion of clinically significant thyroid dysfunction. A comprehensive assessment includes TSH, free T3, free T4, and thyroid antibodies. Adults with TSH at the upper end of the normal range alongside symptoms warrant full assessment. The reference range for TSH is broad and does not preclude clinically meaningful hypothyroidism at values within it.
Lifestyle Support for Thyroid Function
- Adequate iodine: the primary mineral required for thyroid hormone synthesis, available from dairy, fish, and seaweed
- Selenium: essential for conversion of T4 to the active T3 form, found in Brazil nuts, fish, and meat
- Avoiding severe caloric restriction: chronic dieting suppresses T3 production as an adaptive metabolic response
- Zinc: required for thyroid hormone receptor sensitivity and T4 to T3 conversion