16/02/2026
You may have got the message that stress was bad for the thyroid. Let's take that from an airy fairy concept and ground it into reality by looking at the why.
1. Chronic stress and elevated cortisol can suppress the hypothalamic–pituitary–thyroid (HPT) axis
Your thyroid doesn’t work in isolation. It’s controlled by a feedback loop between your brain and your thyroid gland.
When stress is ongoing, cortisol stays elevated. High cortisol signals to the brain that this is not a “safe” time to prioritise growth, repair, or reproduction. Thyroid signalling can be dialled down as a result.
Over time, this can mean lower TSH output, altered thyroid hormone production, or simply a reduced responsiveness of the whole system.
In simple terms: your body shifts into survival mode, and metabolic efficiency becomes secondary.
2. Stress can promote the conversion of T4 into rT3 instead of T3
Your thyroid mainly produces T4, which must be converted into T3, the active hormone that actually drives metabolism, energy, and temperature regulation.
Under stress, the body can increase conversion of T4 into reverse T3 (rT3). Reverse T3 is essentially inactive. It blocks receptor sites without producing the same metabolic effect.
This is thought to be a protective adaptation during stress or illness, conserving energy. But chronically, it can leave you feeling flat, cold, foggy, and struggling with weight despite “normal” thyroid labs.
3. Stress can induce inflammation and immune dysregulation
Chronic stress alters immune signalling and can increase inflammatory cytokines.
In people genetically predisposed to autoimmunity, this matters. Heightened inflammatory tone and immune imbalance can aggravate conditions such as Hashimoto’s or Graves’.
Stress doesn’t “cause” autoimmunity on its own, but it can act as an amplifier. If the immune system is already reactive, stress can pour fuel on the fire.
4. Stress can deplete nutrients essential for thyroid function
Thyroid hormone production and conversion rely on adequate nutrients including selenium, zinc, iodine, iron, and B vitamins.
Stress increases nutrient demand and can impair digestion and absorption. Elevated cortisol also shifts how the body utilises certain micronutrients.
Over time, this creates a double hit: increased need and reduced availability.
The result? Even if your thyroid gland itself is structurally fine, it may not have the raw materials required to function optimally.
I've talked a lot about how most thyroid conditions are diagnosed in perimenopausal women. I've also talked a lot about how our stress buffers are reduced in perimenopause. As you can see it is a bit of a vicious cycle especially when you add in a few other lifestyle factors.
I am running a free webinar Tuesday the 24th to help you better understand why stress hits harder past 35 and give you some tools to stop the slide.
I will pop the link to join in the comments 🦋