Hypothyroidism — an underactive thyroid — affects an estimated 5–10% of the population, with a large share of cases going undiagnosed. Why? Because the standard blood test measures only TSH — and a normal TSH doesn't mean optimal thyroid function.
How to read the numbers: Target = the value we aim for · Risk = what to watch out for · Term = a key term or marker worth knowing
Functional optimum
Laboratory reference ranges for TSH are wide, and some experts regard 1–2 mIU/L as a functional optimum, although there is no single consensus. If you have symptoms such as fatigue or feeling cold despite a normal TSH, discuss the other thyroid hormones with your doctor.
Always test together
TSH is only the signal from the brain, while fT4 and fT3 show how much thyroid hormone your body actually has available. If a disorder is suspected, ask for TSH together with fT4 and fT3, and possibly antibodies too.
Have subclinical hypo
Subclinical hypothyroidism means a slightly raised TSH with still-normal hormone levels, and it becomes more common in women with age; the percentage is an estimate and varies widely between studies. Women over forty with fatigue or weight gain should have their thyroid checked.
What the lab measures vs. what a biohacker measures
Standard test: TSH. The full picture: TSH + free T4 + free T3 + reverse T3 + antibodies (anti-TPO, anti-TG). The difference is fundamental. You can have a normal TSH and still have suboptimal conversion of T4 into active T3.
Fatigue despite enough sleep, cold hands and feet, slowed thinking, thinning of the outer third of the eyebrows, dry skin, constipation, weight gain without any change in diet — these are classic signs of hypothyroidism that get blamed on "age" or "stress".
Hashimoto's thyroiditis
The most common cause of hypothyroidism in the developed world is autoimmune — Hashimoto's disease. The immune system attacks the thyroid. Conventional medicine treats it only once the gland fails. Biohacking asks: what triggers the autoimmune attack, and can it be slowed down?
