You wear a sweater when your family's in t-shirts. You layer under blankets in July. Your hands stay cold year-round, even wrapped around a warm mug. You mention it at your family doctor's appointment. They order a TSH. It comes back normal. That's where the conversation usually ends.
Cold intolerance (the kind that shapes your daily life, has you reaching for sleeves in summer, has you convinced something is off) rarely lives in a normal TSH result. What your family doctor is missing isn't negligence. It's the fact that TSH is one number on a bigger panel.
Subclinical hypothyroidism affects 4 to 8 percent of adults, rising to about 20 percent in women over 60 (Biondi, Cappola, Cooper, 2019, PMID: 31287527). Most never find out because their TSH sits in the normal range while their tissues are freezing. Sometimes the problem isn't underactive thyroid function. Sometimes it's incomplete testing. Sometimes it's ferritin. Sometimes it's perimenopause rewriting everything.
TSH Is One Number on a Bigger Panel
The problem starts with the test itself. TSH is the pituitary signal telling your thyroid to work harder. It's useful. It's cheap. Most labs nail the measurement.
But TSH only captures the signal, not the delivery. Your pituitary might be yelling at your thyroid. Your thyroid might be hearing it. Neither of those tells you if the active hormone reaches your cells, or if your body can use it.
A 2016 review in Clinical Medicine and Research acknowledged that TSH is the most useful single test but noted clear limitations: Free T4 assays often show poor accuracy, Free T3 testing has even more limitations, and a meaningful subset of patients languish in a gray zone that TSH-only screening ignores (Sheehan, 2016, PMID: 27231117). Most family doctors aren't trained to interpret that gray zone. A Naturopathic Doctor is.
What a Full Thyroid Panel Actually Includes
When a Naturopathic Doctor orders a complete thyroid workup, we're not just checking if your thyroid is on or off. We're mapping the entire conversion pathway, from production to activation to cellular response:
- TSH. The signal from your pituitary. Normal is roughly 0.5 to 5 mIU/L, though many functional practitioners target 1 to 3. A normal TSH doesn't rule out thyroid dysfunction if other markers are off.
- Free T4. The inactive form circulating in your blood. Your cells still have to convert it into the active hormone before it does anything.
- Free T3. The active hormone your cells actually use. This is where the energy comes from, where heat generation turns on. Free T3 tells you whether conversion is working, and whether your body can stay warm.
- Reverse T3. The inactive storage form. When you're stressed, iron-deficient, or nutritionally burnt out, your body makes more reverse T3 instead of Free T3. It's a metabolic brake. Too much reverse T3 competes for receptors and blocks heat production.
- TPO antibodies. The immune marker for Hashimoto's thyroiditis. About 90 percent of Hashimoto's patients test positive. You can have elevated TPO antibodies for years while TSH sits normal, with inflammation quietly driving fatigue, cold intolerance, and brain fog.
- Thyroglobulin antibodies. The second autoimmune marker. 50 to 80 percent of Hashimoto's patients test positive. Combined with TPO, this paints a clearer picture of autoimmune burden.
Most Canadian labs will run TSH and Free T4 if you ask. Many will run TPO antibodies. Free T3 and reverse T3 require more specific orders, and most primary care doctors rarely request them. Lab literacy matters.
Ferritin: The Iron Story Nobody Tested
You mention cold intolerance. Your family doctor orders TSH. Normal. Case closed. Half the time they never check ferritin.
Ferritin (your iron storage marker) is essential for thyroid hormone conversion. Three enzymes called deiodinases convert T4 into the active T3. These enzymes require iron. No iron, slow conversion. Your thyroid produces hormone. Your body can't activate it. You freeze.
Iron deficiency also disrupts thyroid peroxidase activity, the enzyme that builds thyroid hormone in the gland. It impairs T4 to T3 conversion in the liver and kidneys. Low ferritin shifts the balance toward reverse T3 instead of Free T3. You get less active hormone and more metabolic brake.
Research on iron-deficient women (with or without frank anemia) documented impaired thermogenesis (the heat-generating process that keeps you warm). Those women had lower metabolic rates in the cold, lower core body temperatures, and faster drops in temperature when exposed to cold, compared to iron-replete controls (Lukaski, Hall, Nielsen, 1990, PMID: 2241732; Brigham and Beard, 1996, PMID: 8989508). The mechanism is exactly what you'd predict: reduced thermogenesis and impaired conversion.
Standard lab ranges for ferritin are 12 to 200 ng/mL for women. But if you're cold, fatigued, or struggling with thyroid function, many Naturopathic Doctors target ferritin above 50 to 70 ng/mL to support conversion. Your family doctor often doesn't order ferritin. Most people never connect iron to being cold.
Perimenopause Complicates All of This
If you're between 35 and 55, thyroid dysfunction in perimenopause can be almost invisible to standard testing.
Estrogen and thyroid are tangled. As estrogen drops, it changes how thyroid-binding globulins circulate (the proteins that carry thyroid hormone through your blood). Lower estrogen doesn't affect thyroid hormone production as much as it changes how much is bioavailable to cells. TSH can climb. Free T4 looks borderline. Free T3 drops. You get cold, brain fog, fatigue, weight gain, and insomnia (symptoms often blamed on menopause alone).
A 2023 analysis in Deutsches Ärzteblatt International reported that a substantial subset of perimenopausal women develop subclinical hypothyroidism, with the frequency highest in older perimenopausal age groups (Frank-Raue and Raue, 2023, PMID: 37013812). Without a full panel, both systems get lumped together. If you're approaching or in perimenopause and cold, a complete thyroid panel is non-negotiable. For the broader picture, see our piece on <a href="/blog/normal-bloodwork-what-your-doctor-isnt-testing">what standard bloodwork doesn't check</a>.
What to Do This Week
- Request a complete panel. Ask for TSH, Free T4, Free T3, reverse T3, TPO antibodies, thyroglobulin antibodies, and ferritin. Write these down. If your family doctor resists, bring them the Sheehan 2016 paper showing the limitations of TSH-only screening.
- Track your temperature patterns. For two weeks, take your resting body temperature each morning before getting out of bed. Normal is around 37°C (98.6°F). Below 36.6°C suggests metabolic slowdown. Bring the log to your appointment.
- Document cold symptoms. When do your hands go cold? Summer, winter, both? After meals? With stress? In air conditioning? Thyroid dysfunction looks different from poor circulation or Raynaud's. A Naturopathic Doctor reads those patterns.
- Eat ferritin-supporting foods. Grass-fed beef, wild salmon, spinach, lentils, fortified cereals. Labs will tell you whether you actually need to act. If ferritin is below 50 ng/mL, dietary and supplement support usually follows.
- Limit reverse T3 triggers. High stress, crash dieting, intensive exercise without recovery, refined carbohydrates. These amp up reverse T3 and suppress Free T3.
- Book a Naturopathic Doctor consultation if the full panel comes back looking normal but you're still cold.
How a Naturopathic Doctor Investigates "Always Cold"
Naturopathic Doctors in Ontario don't prescribe pharmaceutical thyroid hormones. That's outside our scope of practice. What we do is identify what's actually happening.
We run the full panel your family doctor didn't order. We measure ferritin. We graph the ratio of Free T3 to reverse T3. We check for TPO antibodies smoldering under a normal TSH. We correlate lab numbers with history: stress patterns, diet crashes, sleep loss, menstrual changes.
If thyroid function is intact but you're cold, we look at ferritin, selenium, zinc, copper, and digestion. If antibodies are elevated, we outline anti-inflammatory and gut-healing protocols. If conversion is the issue, we support selenium, zinc, and iodine appropriately. If stress is depleting reverse T3, we work on sleep, nervous system regulation, and nutrient repletion.
Many people feel significantly warmer and more energized once the full panel is run and they start addressing what it shows. Not everyone needs thyroid medication. Many never did. They needed ferritin. They needed rest. They needed someone to actually read the whole panel.
Frequently Asked Questions
Why am I always cold?
Cold intolerance has multiple roots: subclinical hypothyroidism (elevated TSH with normal Free T4), incomplete thyroid conversion (low Free T3, high reverse T3), iron deficiency blocking deiodinase function, autoimmune thyroiditis driving inflammation, perimenopausal estrogen shifts, chronic stress raising reverse T3, or metabolic adaptation to chronic undereating. A full thyroid panel plus ferritin usually pinpoints which one.
Is a normal TSH enough to rule out thyroid issues?
No. TSH is a pituitary signal, not a measure of thyroid hormone activity in your cells. You can have normal TSH while Free T3 is low, reverse T3 is elevated, or TPO antibodies are attacking your thyroid. Research suggests TSH-only screening misses a meaningful subset of symptomatic patients. A full panel is the standard of functional medicine, even though primary care rarely orders it.
What's the difference between TSH and Free T3?
TSH is the pituitary's command: make more hormone. Free T3 is the actual hormone active in your cells: generate heat, speed metabolism, think clearly. You can have normal TSH (normal command) while Free T3 is low (broken delivery). TSH tells you if your thyroid heard the signal. Free T3 tells you if your body got the message.
Can low iron make you cold?
Yes. Iron is required for thyroid peroxidase (making thyroid hormone), deiodinases (converting T4 to T3), and thermogenesis (heat production). Low ferritin impairs all three. Research on iron-deficient women without anemia documented lower metabolic heat production and slower core temperature recovery in the cold. Many people with cold intolerance and normal thyroid labs simply have low ferritin.
Can a Naturopathic Doctor help if my thyroid tests are normal?
Yes, if "normal" is hiding incomplete testing. If you've only had TSH checked and you're cold, a Naturopathic Doctor orders the full panel. If the full panel comes back normal but you're still cold, we investigate ferritin, selenium, zinc, digestion, stress hormones, and sleep. Naturopathic Doctors in Ontario don't prescribe thyroid medication, but we can identify nutritional gaps, support conversion enzymes, reduce inflammatory load, and help your body work better with the hormones it has.
References
- Biondi B, Cappola AR, Cooper DS. Subclinical Hypothyroidism: A Review. JAMA. 2019;322(2):153-160. PubMed: 31287527.
- Sheehan MT. Biochemical Testing of the Thyroid: TSH is the Best and, Oftentimes, Only Test Needed. Clin Med Res. 2016;14(2):83-92. PubMed: 27231117.
- Brigham D, Beard J. Iron and thermoregulation: A review. Crit Rev Food Sci Nutr. 1996;36(8):747-763. PubMed: 8989508.
- Lukaski HC, Hall CB, Nielsen FH. Thermogenesis and thermoregulatory function of iron-deficient women without anemia. Aviat Space Environ Med. 1990;61(10):913-920. PubMed: 2241732.
- Frank-Raue K, Raue F. Thyroid dysfunction in peri- and postmenopausal women: cumulative risks. Dtsch Arztebl Int. 2023;120(18):311-316. PubMed: 37013812.
This article is for educational purposes only and does not replace professional medical advice. Naturopathic Doctors in Ontario do not prescribe pharmaceutical thyroid medication. If you suspect thyroid dysfunction, work with both your family doctor and a Naturopathic Doctor to get complete testing and coordinated care.
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