Your Iron and Thyroid Issues Intersect. Here's How.

You're exhausted no matter how much you sleep

You're seeing more hair in the shower drain than you'd like to admit

You bring a sweatshirt everywhere because you're always cold (but everyone else is fine).

You have anxiety that feels like it's coming from your body and not your brain.

Your symptoms seem to get worse at certain times of the month.

So, you Google your symptoms and get some labs done. You ferritin is low, or your thyroid seems sluggish, or maybe it's both. You start taking iron supplements and/or thyroid medication.

But you're still waiting to feel better, and it doesn't seem to be happening.

The reason things aren't improving is often what's driving both problems in the first place. Your stomach acid.

Iron and thyroid function are connected in a loop with gut health, and if you only address one without understanding what's driving both, you might keep spinning your wheels.

The Loop You Need to Understand

Your thyroid needs iron to convert T4 (the inactive thyroid hormone) into T3 (the active form your cells can actually use). So low iron means low conversion. Even if your TSH looks fine and you're producing T4, it might not be getting where it needs to go.

But here's where it gets interesting. Low iron usually isn't because you're not eating enough iron-rich foods or taking enough in supplements. A lot of the time, the real problem is that you're not absorbing what you take in, because your stomach acid is low.

Stomach acid is what breaks down the proteins and minerals in your food well enough for your small intestine to absorb them. When stomach acid is low, iron absorption drops. Zinc absorption drops too, and zinc is required for stomach acid production in the first place!

So, you end up with less zinc, which means less stomach acid, which means less iron absorption, which means less thyroid conversion, which means more fatigue, more brain fog, more of everything you've been trying to fix.

Round and round, getting worse and worse. It's like being on the worst merry-go-round ever.

Then there's the gut connection that ties it all together. Chronic low stomach acid creates an environment where dysbiosis (an imbalance of gut bacteria) can take hold. A disrupted gut microbiome contributes to intestinal permeability, also called leaky gut. And a leaky gut drives inflammation, which further impairs thyroid conversion and can trigger the immune response that leads to Hashimoto's.

Gut issues also set you up for histamine intolerance. Your gut can start being overpopulated with bacteria that produce histamine, and inflammation can also increase histamine production and lower the amount of enzymes produced that can clear it out. This causes a variety of symptoms often mistaken for low iron or thyroid dysfunction, since many overlap.

So, when someone asks, "will I feel better when my ferritin comes up?" my honest answer is maybe, but only if we also figure out why it was low in the first place, and even if that was the reason for your symptoms.

What This Looks Like on Labs

I'm not looking for one dramatic finding. I'm looking for a pattern.

On standard bloodwork, low stomach acid leaves clues: low total protein, low alkaline phosphatase, low magnesium, low iron, low B12. None of these individually sends up a red flag, but together they tell a story.

Thyroid labs worth running (beyond TSH) include free T3, free T4, reverse T3, and thyroid antibodies. A normal TSH with low free T3 points to a conversion problem. Elevated TPO or TG antibodies point to an autoimmune process that almost always has a gut component driving it. High reverse T3 points to inflammation throwing off everything, and that inflammation often starts in the gut.

If your doctor has only run TSH and ferritin, you're working with an incomplete picture.

For functional labs, the Intestinal IQ, GI Map, DUTCH, or OAT can be helpful, but starting with basic bloodwork points us in the right direction.

Some Things You Can Try Right Now

↣ Test your stomach acid at home. The baking soda test isn't perfect clinically, but it's basically free and very easy.

• How to do it: First thing in the morning, before eating or drinking anything, mix a quarter teaspoon of baking soda in about four ounces of warm water and drink it. If your stomach acid is adequate, you should burp within two to three minutes. Little to no burping can suggest low stomach acid. Do it three mornings in a row for a better sense of the pattern.

↣ Support stomach acid before meals.

• Bitter foods like arugula, dandelion greens, and radicchio stimulate digestive enzyme production, bile flow, and stomach acid release when eaten before a meal.

• A tablespoon of raw apple cider vinegar (ACV) in a small amount of water before meals can also help.

One caveat: if you're dealing with histamine reactivity, ACV and some bitter foods can be problematic. If you're not sure if you have histamine reactivity, you can take my free quiz here before adding these in.

↣ Add selenium-rich foods. Selenium is required for thyroid hormone conversion and also helps regulate thyroid antibodies.

• Two brazil nuts a day is the classic recommendation and it's enough. Don't megadose selenium supplements without testing first. More is not better here.

↣ Support zinc through food. Zinc-rich foods include oysters, beef, pumpkin seeds, and chickpeas.

• Again, supplementing without knowing your levels can backfire. Food sources are a safer starting point.

Want to Go Deeper?

If any of this sounds like your body, the next step is figuring out which part of the loop is most active for you. Here are some ways to figure it out.

If you're not sure if gut health, thyroid, or histamine is an issue, and you've been chasing symptoms that don't have a clear explanation, it's worth digging a little. The quiz takes about two minutes and tells you where imbalances may be showing up in your symptoms. Take the quiz →

↣ Get my newly updated Iron Guide eBook! It walks you through optimal ranges, the most helpful iron markers, how to eat for the best iron absorption, and how to supplement safely.

↣ You can order an iron panel directly through Fullscript without a doctor's order. Order the Iron Deep Dive Panel

Ready to take action?

Inside my Histamine Discovery Panel, I use the Fluids iQ Intestinal iQ to look at:

↣ histamine levels

↣ DAO activity (the enzyme that breaks down histamine)

↣ gut barrier integrity (zonulin)

You’ll complete the at-home blood spot test, and I’ll connect your results with your symptoms to give you a clear, personalized breakdown and next steps.

If you just want more of this kind of content, I cover the symptoms most practitioners don't connect in my weekly newsletter. Join the newsletter →

Jennifer Scanlon, MS, FDN-P, holds a Master of Science in Holistic Nutrition and a Bachelor of Health in Cardiopulmonary and Diagnostic Sciences. Before starting her nutrition practice, she spent more than a decade as a respiratory therapist working alongside physicians and nurses as part of the critical care team. Her role included neonatal resuscitation, ventilator management, blood gas analysis, and the assessment of critically ill patients, providing a strong foundation in physiology and clinical reasoning.

After facing her own health challenges that weren't fully explained by conventional testing, Jennifer returned to graduate school, completing her master's capstone on Hashimoto's disease and the gut-thyroid connection. She has since pursued advanced training in functional health assessment and spent years studying thyroid disorders, gut health, iron deficiency, histamine intolerance, MCAS, and the complex interactions between body systems.

Today, Jennifer helps women uncover potential contributors to symptoms that often fall through the cracks of standard evaluations. Her approach combines nutrition, lifestyle factors, functional testing, and conventional lab data to identify patterns and connect the dots between thyroid, gut, histamine, and hormone issues, helping women make sense of symptoms that are often dismissed when standard lab work comes back "normal." Visit the website here.

Disclaimer: I do not diagnose, treat, prevent, or cure any disease or condition. Nothing I share with my clients is intended to substitute for the advice, treatment or diagnosis of a qualified licensed physician. I may not make any medical diagnoses or claim, nor substitute for your personal physician’s care. It is my role to partner with you to provide ongoing support and accountability in an opt-in model of self-care and any changes should be done under the supervision of a licensed physician.