Feeling foggy, forgetful, or like your brain has lost its edge? You’re not imagining it. In this episode of The Dr. Brighten Show, Dr. Jolene Brighten explains what your TSH lab test really tells you and what it doesn’t. Most doctors stop testing after TSH, but this brain-to-thyroid signal is only one piece of your hormonal story.
You’ll learn how thyroid hormones influence energy, metabolism, mood, and focus, why women are far more likely to struggle with thyroid disorders, and which labs and nutrients can help you finally clear the brain fog for good.
Listen to: What Is a TSH Lab Test? Decode the Thyroid Numbers Your Doctor Overlooked
TL;DR — Key Takeaways
- TSH measures brain-thyroid communication, not thyroid output.
- Many women feel hypothyroid symptoms even with “normal” labs.
- Free T3 is your active thyroid hormone — if it’s low, your brain slows.
- Hashimoto’s, stress, and nutrient deficiencies are the real drivers for most women.
- The solution isn’t guessing — it’s testing smarter and supporting holistically.
What Is a TSH Lab Test and Why It’s Not Enough on Its Own
A TSH lab test (thyroid-stimulating hormone test) measures how loudly your brain is “talking” to your thyroid to tell it to make hormones. When your thyroid isn’t responding well, the brain shouts louder and your TSH level goes up.
But here’s the catch: TSH only shows communication, not production or conversion. To truly understand thyroid function, you also need Free T4, Free T3, Reverse T3, and thyroid antibodies.
What You’ll Learn in This Episode
Each of these insights can change how you think about your thyroid and your energy:
- Why brain fog, fatigue, and slow thinking often start with low thyroid hormone, not low willpower.
- The real meaning behind your TSH number and why “normal” on paper may still mean symptoms in real life.
- The optimal TSH range (1.0–2.5 mIU/L) for women — long before the standard “normal” range flags problems.
- How low Free T3 slows your metabolism and mental sharpness (it’s the hormone your brain actually uses).
- The “hibernation hormone,” Reverse T3 and how stress can push your body into energy-saving mode.
- Why Hashimoto’s thyroiditis causes up to 90% of hypothyroidism in women and how to test for it.
- How birth control pills and estrogen therapy can raise thyroid-binding globulin, making your thyroid hormone less available.
- The powerful link between thyroid hormone and mood — why hypothyroidism can mimic depression or ADHD.
- How autoimmunity, gut health, and nutrient deficiencies all drive thyroid dysfunction.
- The overlooked role of selenium, zinc, and vitamin D in calming antibodies and restoring thyroid balance.
- What functional medicine looks for when TSH is “normal” but you still feel off and when to dig deeper.
- Dr. Brighten’s personal story: how she put her own Hashimoto’s into remission (and what triggered a temporary flare postpartum).
Listen to: What Is a TSH Lab Test? Decode the Thyroid Numbers Your Doctor Overlooked
Understanding Your Thyroid: TSH, Free T3, and the Brain Connection
The TSH lab test is your brain’s request line for thyroid hormone, but Free T3 is the song your cells actually play.
When TSH rises, it means your brain is asking for more, but if Free T3 stays low, your body and brain stay in “low-power mode.”
Low thyroid slows down glucose metabolism (your brain’s main fuel), decreases myelin production (the insulation for fast thinking), and reduces dopamine and serotonin synthesis — leaving you foggy, flat, and unmotivated.
Women are disproportionately affected because of autoimmune prevalence, hormonal shifts, and greater sensitivity to nutrient deficiencies.
Studies even show that untreated hypothyroidism leads to reduced prefrontal cortex activity on fMRI — the part of your brain that controls focus, planning, and executive function.
In this episode, Dr. Brighten also explores:
- Why thyroid medication can be life-changing when prescribed and monitored properly.
- How to choose between T4-only therapy (levothyroxine) and combination therapy with T3 or desiccated thyroid.
- How to identify when Hashimoto’s inflammation, not just low hormone, is the true driver of symptoms.
- The nutrients your thyroid factory needs — including iodine, selenium, zinc, iron, vitamin A, manganese, and tyrosine.
- Why blood sugar balance and stress resilience are critical to calming autoimmune activity.
Quick Reference: Optimal Thyroid Lab Ranges
| Test | Optimal Range | What It Tells You |
| TSH | 1.0–2.5 mIU/L | Brain-to-thyroid communication |
| Free T4 | 1.2–1.8 ng/dL | How well thyroid is producing hormone |
| Free T3 | 3.0–4.2 pg/mL | Active hormone your brain and body use |
| Reverse T3 | <15 ng/dL | Energy conservation vs metabolism |
| TPO & TG Antibodies | Negative | Autoimmunity (Hashimoto’s) |
| Ferritin | 70–120 ng/mL | Iron storage critical for thyroid hormone synthesis |
This Episode Is Brought to You By
Dr. Brighten Essentials Thyroid Support — featuring selenium, zinc, coleus forskohlii, and tyrosine to support healthy thyroid hormone production and conversion.
Also mentioned:
Women’s Twice Daily multivitamin (for vitamin A, B2, and manganese)
Vitamin D & Omega Plus for immune and thyroid balance
Beyond the Pill and Is This Normal? by Dr. Jolene Brighten
(Affiliate/sponsor links may provide compensation at no extra cost to you.)
Links Mentioned in This Episode
Resources & Articles:
- Anti-Inflammatory Meal Plan
- Gut Health and Hormones Episode
- Iodine and Hashimoto’s Research
- Endocrine Disrupting Compounds and Fertility
- How Endocrine Disrupting Chemicals Cause Hormone Imbalance
- Are Endocrine Disruptor Chemicals Making It Harder to Get Pregnant? | Dr. Lora Shahine
Research Citations:
- Hu Y, Feng W, Chen H, Shi H, Jiang L, Zheng X, Liu X, Zhang W, Ge Y, Liu Y, Cui D. Effect of selenium on thyroid autoimmunity and regulatory T cells in patients with Hashimoto's thyroiditis: A prospective randomized-controlled trial. Clin Transl Sci. 2021 Jul;14(4):1390-1402. doi: 10.1111/cts.12993. Epub 2021 Apr 9. PMID: 33650299; PMCID: PMC8301566.
- Wang YS, Liang SS, Ren JJ, Wang ZY, Deng XX, Liu WD, Yan YL, Song GH, Li XX. The Effects of Selenium Supplementation in the Treatment of Autoimmune Thyroiditis: An Overview of Systematic Reviews. Nutrients. 2023 Jul 19;15(14):3194. doi: 10.3390/nu15143194. PMID: 37513612; PMCID: PMC10386011.
- Nordio M, Basciani S. Treatment with Myo-Inositol and Selenium Ensures Euthyroidism in Patients with Autoimmune Thyroiditis. Int J Endocrinol. 2017;2017:2549491. doi: 10.1155/2017/2549491. Epub 2017 Feb 15. PMID: 28293260; PMCID: PMC5331475.
Frequently Asked Questions
TSH measures the thyroid-stimulating hormone your pituitary gland produces to tell your thyroid how much hormone to release.
While most labs list up to 4.5 mIU/L as “normal,” research shows women feel best between 1.0–2.5 mIU/L, especially when trying to conceive.
It’s often used as a screening tool, but it misses issues with conversion (T4→T3) or thyroid autoimmunity. A full panel gives the full picture.
Yes. Estrogen raises thyroid-binding globulin, meaning your “total” thyroid hormone can look fine while your free, active hormone drops.
Yes — with the right lifestyle, nutrients, and immune support. Dr. Brighten shares how she personally reduced hers to undetectable levels.
Listen & Subscribe
Listen to: What Is a TSH Lab Test? Decode the Thyroid Numbers Your Doctor Overlooked
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