For about two years, I thought I was just someone who ran cold.
Cold hands, cold feet, a persistent inability to feel warm even in reasonably heated rooms. I layered up while others were fine in a t-shirt. I assumed it was just how I was built.
Then there was the weight that would not shift despite genuine effort. The hair that was coming out more than it used to, noticeable on the shower floor, on my pillow, caught in my hairbrush. The eyebrows that had become thinner at the outer edges without me consciously registering when that had started happening.
And underneath all of it, a tiredness so bone-deep and consistent that I had started explaining it away as just being in my thirties.
None of these things pointed an obvious finger at one cause. But together, they were describing the same organ struggling to do its job.
What the Thyroid Actually Does
Your thyroid is a small butterfly-shaped gland sitting at the front of your neck, and it is responsible for something so fundamental that almost no system in your body operates independently of it.
It produces two primary hormones, T4 and T3, that regulate the metabolic rate of virtually every cell in your body. When hormone levels are adequate, your cells produce energy efficiently, your temperature regulation works, your digestion moves at the right pace, your heart beats at its proper rhythm, and your brain has the chemical environment it needs to function clearly.
When output from the gland drops, everything slows. Not in one dramatic moment. Gradually, across months and years, in ways that are easy to attribute to ageing, stress, or simply not taking good enough care of yourself.
This gradual onset is one of the reasons thyroid dysfunction is so frequently missed or dismissed. The changes happen slowly enough that each new baseline feels normal by the time the next decline arrives.
The Testing Problem
Here is something that frustrates a lot of people who suspect their thyroid is not working optimally, and I think it is worth being honest about.
The standard test measures TSH, thyroid stimulating hormone. TSH is produced by the pituitary gland and acts as a signal to the gland to produce more hormone. When output is low, TSH rises in an attempt to stimulate more production. So a high TSH suggests an underactive thyroid.
The problem is that the reference range used to define normal TSH is broad, and many people experience significant symptoms at TSH levels that fall within the normal range. The range was established using population averages that include people with subclinical dysfunction, which means the upper end of normal may not represent optimal function for many individuals.
Additionally, measuring TSH alone tells you about the pituitary’s signalling but not about what is actually happening at the tissue level. T4 is the inactive storage form of thyroid hormone. It needs to be converted to T3, the active form, in the liver, gut, and other tissues before it can do anything useful. Some people have adequate T4 but poor conversion to T3, meaning their TSH looks normal and their T4 looks normal but their cells are receiving inadequate active hormone.
A more complete picture comes from testing TSH, free T4, free T3, and thyroid antibodies together. This is not always offered as standard. Asking for it specifically, or seeking assessment from a practitioner who takes a comprehensive approach, can make a significant difference in whether the picture becomes clear.
This is an area where working with a knowledgeable healthcare professional matters. I am not suggesting self-diagnosis or self-treatment. But understanding what to ask for is half the battle when your experience does not match what standard testing is showing. See also our Medical Disclaimer.
Hashimoto’s: When the Immune System Attacks
The most common cause of hypothyroidism in developed countries is not the gland itself failing. It is the immune system attacking it.
Hashimoto’s thyroiditis is an autoimmune condition in which the immune system produces antibodies that gradually damage thyroid tissue over time. It can exist for years, sometimes decades, before hormone levels drop enough to show on a standard test. During that entire period, the inflammatory process is active and the person may be experiencing symptoms without any conventional explanation for them.
Thyroid antibody testing, specifically TPO antibodies and thyroglobulin antibodies, can identify this immune activity long before TSH or T4 levels become obviously abnormal. This matters because addressing the autoimmune component — the underlying immune dysregulation — requires a different approach from simply supplementing with thyroid hormone.
Gluten sensitivity has a well-documented association with Hashimoto’s. The protein structure of gliadin, found in gluten, has structural similarities to thyroid tissue proteins. In people with intestinal permeability, gliadin fragments entering the bloodstream can trigger an immune response that cross-reacts with thyroid tissue. This is not a claim that everyone with this condition is gluten sensitive. But for people with confirmed thyroid antibodies, a trial of strict gluten elimination for at least three months is something that appears frequently in the functional medicine literature as worth exploring.
Selenium is another piece of the Hashimoto’s puzzle worth knowing about. The thyroid contains the highest concentration of selenium of any organ in the body. Selenium-dependent enzymes are essential for hormone synthesis and for converting T4 to T3. Several studies have found that selenium supplementation reduces TPO antibody levels in people with Hashimoto’s. Brazil nuts, two to three per day, provide approximately the right amount without the risk of excess that comes with supplemental selenium at high doses.
The Lifestyle Factors That Quietly Affect Thyroid Function
Even outside of autoimmune thyroid disease, several things in daily life can meaningfully affect how well the gland produces and converts its hormones.
Chronic stress suppresses thyroid function through two distinct mechanisms. First, elevated cortisol directly inhibits the conversion of T4 to T3. Second, the stress response promotes the conversion of T4 into reverse T3 instead, a metabolically inactive molecule that actually blocks T3 receptors. So under chronic stress, you can have normal T4 levels and still have inadequate active T3 at the cellular level.
This is one of the reasons people under sustained long-term stress often develop a symptom picture that looks remarkably like hypothyroidism, because at the cellular level, they are experiencing something functionally similar.
Iron deficiency impairs thyroid hormone synthesis directly. The enzyme responsible for producing thyroid hormone, thyroid peroxidase, requires iron to function. This is another reason why investigating ferritin levels alongside thyroid panels gives a more complete picture, particularly in women who may have low ferritin without overt anaemia.
Iodine is necessary for thyroid hormone production but is also one of the more complicated nutrients in this area. Both deficiency and excess can impair function. In populations with adequate dietary iodine from seafood and dairy, supplementing with additional iodine is not straightforwardly beneficial and may actually worsen Hashimoto’s in some individuals. This is not an area for guesswork.
What Changed When I Finally Got Answers
Getting a full thyroid panel rather than just TSH was the first genuinely useful step. When my free T3 came back at the lower end of its reference range while my TSH looked technically normal, it gave me and the practitioner I was working with something concrete to address rather than continuing to be told everything looked fine.
The changes I made were not about medication, at least not initially. Reducing chronic stress load was the most impactful single factor, partly because of what I now understood about cortisol and T4 to T3 conversion. Addressing low ferritin came next. Removing gluten for a trial period, not because I believed in it categorically, but because the mechanism made enough sense to be worth testing honestly.
The cold hands and feet improved first. Then the energy, gradually. The hair loss slowed over several months. The outer edges of my eyebrows, slowly, began to fill back in.
These are not dramatic transformations. But after years of being told everything was normal while feeling very far from it, they felt like proof that paying attention to the right things actually matters.
If you have been told your tests are normal but you still feel like something is off, I hope this gives you some useful language for the conversations ahead. You know your body better than a single number on a lab report does. Trust that.
Drop a comment below if any of this resonated with your experience. Particularly if you have navigated the testing process and found something that was missed the first time around.
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