Hashimoto's Antibodies: What They Are, What They Tell You, and How to Lower Them

Anti-TPO = 100. I remember that lab result like it was yesterday. TSH 9, an ultrasound where my thyroid looked like anything but a butterfly, and one number with nothing next to it except an arrow pointing up. The first question I asked was "what is this now?" The second, "is 100 a lot?" The third, which I only asked much later: "why is nobody telling me what to do with this number?"

If you're also sitting there with your lab results in hand, googling "Hashimoto's antibodies," this post is for you. No medical jargon, no panic, no promises that you'll be cured in 30 days. Just what you really need to know, with sources you can rely on.

What Hashimoto's antibodies are, in simple terms

With Hashimoto's, the immune system mistakenly starts treating the thyroid as an intruder. Antibodies are like wanted posters your body puts out for parts of its own thyroid gland. The more of them there are, the louder the immune system is in its mistake.

On your lab report, you'll most often see two:

• Anti-TPO (thyroid peroxidase antibodies). TPO is an enzyme, a little "worker" in the thyroid that helps produce hormone. Anti-TPO are the most common and most important marker of Hashimoto's.
• Anti-Tg (thyroglobulin antibodies). Thyroglobulin is a protein in which the thyroid "stores" the raw material for hormones. Anti-Tg often show up together with anti-TPO, but less often on their own.

Now, a few things I wish someone had told me right away:

Positive antibodies are not the same as disease. The British Thyroid Foundation states that about 10% of people without any thyroid disease have positive anti-TPO. A large US population study (NHANES III) showed a similar picture: roughly one in ten people has positive antibodies, more often women and more often with age. So antibodies alone are a signal, not a verdict.

There is also Hashimoto's without positive antibodies. It's called seronegative autoimmune thyroiditis. In that case, the diagnosis is based on ultrasound and hormone levels. A 2014 study by Rotondi and colleagues showed that these patients on average have a milder clinical picture and less often develop overt hypothyroidism. If your endocrinologist said "Hashimoto's" and your antibodies are negative, you are not a glitch in the system.

How to read your lab results

This is where most of us make the same mistake. We compare our number to a friend's, then to a number from some Facebook group, and then we panic.

Reference ranges depend on the lab. There is no single universal cutoff for anti-TPO. An Italian study that compared six different laboratory methods showed that the upper limit of "normal" differs from method to method, because each test manufacturer uses a slightly different measuring principle. Cleveland Clinic puts it directly: don't compare a result from one lab to another lab's reference range.

In practice, this means:

• Your 100 at one lab is not the same as someone else's 100 at another.
• If you track your antibodies over time, always have them done at the same lab, using the same method.
• Look at the trend over months, not a single number. Antibodies naturally fluctuate, and one spike means nothing.

Antibody levels don't determine your medication dose. Your endocrinologist sets your levothyroxine dose based on TSH and fT4, not antibodies. That's why you'll often hear that antibodies "don't need to be retested." That's true when it comes to the dose of your pill. But, as you'll see a bit further down, that's not the same as "antibodies don't mean anything."

Antibodies don't measure how damaged the gland is. That's what ultrasound and hormone levels are for. Antibodies tell you more about how active the immune process is right now, and that's exactly the part you can influence with your everyday habits.

Hashimoto's and hypothyroidism are not the same, so they aren't treated the same

This is the sentence that made me start this blog in the first place: Hashimoto's is the cause, hypothyroidism is the consequence. And not in every woman.

Simply put:

• Hashimoto's is an autoimmune process. Its markers are antibodies and ultrasound findings. There's no medication that "switches it off." You influence it by reducing inflammation: through diet, sleep, stress, movement, and replenishing what's missing.
• Hypothyroidism is the state in which the thyroid no longer produces enough hormone. Its markers are TSH and fT4. It's treated with hormone replacement, meaning levothyroxine.

The American Thyroid Association (ATA) states clearly: if you have high antibodies but normal TSH and fT4, you don't need hormone therapy. That confuses a lot of women, because they walk out of the doctor's office with a diagnosis and no plan at all. As if they were told "you have Hashimoto's, see you in six months."

But those six months aren't time for waiting. A twenty-year follow-up in the small English town of Whickham (the Whickham Survey) showed that women with positive antibodies alone have about a 2% chance per year of developing hypothyroidism. In women who have slightly elevated TSH on top of the antibodies, that risk is about 4% per year. It's not much from year to year, but it adds up. That's why regular checkups matter, and why it makes sense to work on inflammation while your hormones are still normal.

And what does levothyroxine do to antibodies? Interestingly, it does something. A German study (Schmidt and colleagues, 2008) followed women with Hashimoto's on levothyroxine for five years. Their antibodies dropped by 70% on average, but only one in six became fully negative. So: the pill is not the enemy, and for many it calms things down, but on its own it rarely brings antibodies down to zero. I wrote more about what treatment can and can't do in Can Hashimoto's be cured?.

Why stable TSH doesn't mean stable Hashimoto's

"Your results look great." And you wake up feeling like you've been hit by a truck. You bloat after every meal. You forget why you walked into a room. You're cold in July.

You're not making it up. And no, it's not "all in your head."

TSH measures one thing: whether you have enough hormone. It doesn't measure how agitated your immune system is. And this is where three studies have proven especially important:

1. Austrian study (Ott and colleagues, 2011). They compared 426 women who all had normal hormone levels. Those with high anti-TPO (above 121 IU/mL) had 6.7 symptoms on average, and those with low levels had 4.1. TSH was the same in both groups. More fatigue, more irritability, dry hair, lower quality of life. The difference wasn't in the hormones. It was in the antibodies.

2. Chinese study (Li and colleagues, Scientific Reports, 2024). In women with Hashimoto's and normal hormone levels, higher antibodies went hand in hand with higher inflammatory markers in the blood and with more pronounced symptoms: bloating, fatigue, forgetfulness, feeling cold.

3. Norwegian randomized trial (Guldvog and colleagues, Annals of Internal Medicine, 2019). This one is the most dramatic. Women with Hashimoto's who had normal hormone levels on treatment but still had persistent symptoms were split into two groups. One continued standard treatment, and the other had their thyroid surgically removed. After 18 months, the group whose thyroid was removed had significantly less fatigue and a better quality of life, and their antibodies dropped from over 2,000 to about 150.

To be clear: this is not a recommendation to have your thyroid removed. Surgery carries its own risks: in a later study of 154 patients operated on outside the trial itself, about 6% had permanent complications, and the researchers couldn't rule out a placebo effect either. But the study's message is important: in some women, the symptoms come from the autoimmune process itself, not from a lack of hormone. When that process quiets down, the symptoms ease.

So normal TSH means the hormone has been replaced. It doesn't mean the inflammation is calm.

How to recognize that your Hashimoto's isn't calm, even though your TSH is normal:

• fatigue that doesn't go away even after enough sleep
• bloating and changes in digestion with no clear reason
• brain fog and forgetfulness
• facial puffiness and water retention
• joint and muscle pain
• flare-ups after stress, illness, or sleepless nights

If you recognize yourself here, it's not a reason to panic. It's a reason to look at what the pill doesn't cover.

Remission: what's realistic and what isn't

The word "remission" gets used online for all sorts of things. Let's clear it up in three sentences.

Remission of hypothyroidism means the thyroid produces enough hormone again without medication. This is documented in the medical literature, but it's a minority outcome and should only be assessed under an endocrinologist's supervision. Never, ever stop your levothyroxine on your own.

Remission of the autoimmune process, in the sense of antibodies disappearing forever, is rare. As we've seen, even after five years of treatment only one in six women becomes fully negative.

What's realistic and achievable is the third kind: antibodies trending down over months, less inflammation, a more stable gland, and days when Hashimoto's isn't the main character in your life. That's the remission I'm chasing. And that's the one I can honestly promise you is worth the effort.

What can raise your antibodies

Before we talk about what lowers antibodies, it's worth knowing what raises them. Sometimes it's easier to remove the trigger than to put out the fire.

• Too much iodine. A large Chinese study published in the New England Journal of Medicine (Teng and colleagues, 2006) followed three regions with different iodine intakes. In the region with mild iodine deficiency, autoimmune thyroiditis developed over five years in 0.2% of people, in the region with more than adequate iodine in 1%, and with excessive iodine in 1.3%. That doesn't mean you should avoid iodized salt. It means you shouldn't take supplements with kelp, seaweed, or high doses of iodine "for your thyroid" on your own.
• Pregnancy and the postpartum period. The immune system calms down during pregnancy and then "bounces back" after birth. More on that in a separate section below.
• Selenium and vitamin D deficiency. Both are linked to higher antibodies, and both are common in women with Hashimoto's.
• Chronic stress and lack of sleep. Stress raises cortisol, and cortisol directly affects the same hormonal axis that controls the thyroid and shifts the balance of immune cells. The evidence that stress causes Hashimoto's is weak, so please don't blame yourself for your diagnosis. But that stress worsens an already existing process, that I'll sign off on. I wrote about how I learned this the hard way in Bikini Fitness and Hashimoto's: 10 Things I Learned During Bodybuilding Prep.
• Gluten, in women who are sensitive to it. Celiac disease and Hashimoto's share a genetic background and often go together.

What science says helps lower antibodies

Here's the part you probably opened this post for. A holistic approach isn't esoteric, and it isn't a replacement for treatment. It's everything you do alongside treatment, every day, that has a measurable effect. Let's go in order, starting with what has the most evidence.

Selenium

Selenium is the best-researched supplement for Hashimoto's. The largest analysis to date (Huwiler and colleagues, Thyroid, 2024) pooled 35 randomized trials and showed that selenium significantly lowers anti-TPO, both in women taking levothyroxine and in those who aren't. The effect on anti-Tg was not significant.

Two important things. First, selenium has a narrow "window": too little doesn't work, too much is harmful. Second, the effect lasts as long as you take it. I broke down which form, how much, and for how long in Thyroid supplements: where to start. And if you love Brazil nuts, know that they're the richest natural source of selenium, but the amount in them is unpredictable, so don't count on them as your only source.

Vitamin D

Vitamin D deficiency in women with Hashimoto's is the rule rather than the exception. A meta-analysis of eight randomized trials with a total of 652 patients (Zhang and colleagues, 2021) showed that vitamin D supplementation lowers both anti-TPO and anti-Tg. One detail I found especially interesting: the effect only showed up when supplementation lasted longer than three months. So, patience. And before you start, get your vitamin D level tested so you know your starting point.

Gluten

A Polish pilot study (Krysiak and colleagues, 2019) followed 34 women with Hashimoto's who weren't on treatment yet. After six months without gluten, their antibodies dropped and their vitamin D levels rose slightly.

The study is small and not randomized, and later research paints a mixed picture. My take: for some women gluten makes a difference, for others it doesn't. Before you cut it out, ask your doctor to test you for celiac antibodies (tTG), because once you stop eating gluten, that test is no longer reliable.

An anti-inflammatory diet and body weight

There's no single magic diet here, and anyone selling you one isn't telling the truth. Here's what the studies show:

• An Italian study (Esposito and colleagues, 2016) of 180 people with Hashimoto's and excess weight showed that a lower-carbohydrate diet lowered anti-TPO by about 44% in just three weeks, while in the control group it didn't change significantly.
• A Polish study (Ostrowska and colleagues, 2021) of women with Hashimoto's and obesity showed that antibodies dropped in everyone who reduced their calorie intake, and more so in those who also cut out foods they individually reacted to.

Just so there's no confusion, because I know you're reading me after my bikini post too: carbs are not the enemy, bad sources of carbs are. What these studies essentially show is that less sugar, less processed food, and less body fat mean less inflammation. And less inflammation means a calmer immune system. You don't have to eat eggs and broccoli for the rest of your life. You have to eat smart, 80:20.

What I actually eat, what I avoid, and which nutrients I always check, I wrote about in Hashimoto's Diet: What to Eat and What to Avoid. And if you're wondering why the scale can stall with Hashimoto's even when you're doing everything right, take a look at Why does weight loss stall with Hashimoto's?.

The hardest part isn't knowing what to eat. The hardest part is cooking it every day without spending half your life in the kitchen. That's exactly why I created The Hashimoto Cookbook: recipes without inflammatory foods, with enough protein, healthy fats, and smart carbs, that come together quickly and don't taste like a diet.

Movement

A Chinese study published this year in BMC Endocrine Disorders (Ma and colleagues, 2026) of 105 patients with Hashimoto's showed that those who exercised more, at a higher intensity, had lower anti-TPO antibodies. A Croatian study of over 230 female patients (Vuletić and colleagues, 2025) showed that recreational exercise is associated with lower inflammatory markers.

The key word is recreational. Training you choose, dose yourself, and recover from afterward. Not training you do on four hours of sleep to "earn" your dinner. That's just one more stressor.

Sleep and stress

This one doesn't have its own meta-analysis with a number at the end, but it has something no study can take away from me: my own experience. Two bad days of stress and no sleep can undo what you've been building for two weeks. Sleep is when the immune system "resets." Stress is a signal to the body that it's in danger, and an immune system in danger gets jumpier.

That's why I treat stress like a macronutrient. It gets planned, measured, and managed. Phone down in the evening, the same bedtime, a few minutes of breathing with long exhales. Nothing spectacular. But it works.

Antibodies and pregnancy

I'm writing this part separately because it concerns a lot of you who read me, and it gets talked about far too little in doctors' offices.

According to the 2017 American Thyroid Association guidelines, between 2% and 17% of pregnant women have positive antibodies, and positive anti-TPO are associated with a higher risk of miscarriage and preterm birth. After giving birth, roughly half of women with positive anti-TPO develop some kind of thyroid dysfunction.

What helps and what doesn't:

• Levothyroxine "just in case" is not the answer. The large British TABLET trial (New England Journal of Medicine, 2019) of 952 women with positive anti-TPO and normal hormone levels showed that levothyroxine before conception did not increase the number of live births. Treatment makes sense when hormone levels are off, not just because antibodies are positive.
• Selenium is promising. An Italian study (Negro and colleagues, 2007) showed that among pregnant women with positive anti-TPO, postpartum thyroid dysfunction was less common in those who took selenium (29%) than in those who got a placebo (49%). But during pregnancy, nothing gets added without your doctor.
• If you're planning a pregnancy, tell your OB-GYN and endocrinologist that you have Hashimoto's, get your TSH, fT4, and antibodies tested before conception, and agree on a plan for checkups during pregnancy and after birth.

How I do it in practice

If all of this feels like too much at once, I get it. It did for me too. So here's how I would start if I were back at the beginning:

1. Treatment comes first. Levothyroxine exactly as prescribed, in the morning on an empty stomach, with a glass of water. This isn't the phase for experiments.
2. Get the tests that make sense. TSH, fT4, anti-TPO, anti-Tg, vitamin D, ferritin, B12. So you know your starting point.
3. One change per month. Not ten. A month of consistent sleep, or a month without gluten, or a month on selenium agreed on with your doctor. When you change everything at once, you don't know what worked.
4. A symptom journal. Energy, sleep, digestion, mood, puffiness. Symptoms shift within a few weeks, antibodies within a few months. Don't wait for the lab to tell you you're better.
5. Recheck antibodies every 3 to 6 months, always at the same lab. And look at the trend, not a single number.

If you don't know where to start, I've broken all of this down into three weeks, step by step, in my free guide. And when you get to the "what do I eat today" part, there's the cookbook.

Your antibodies are not your grade. They're not a punishment either. They're just the voice of your immune system, and you have far more influence over how loud it is than anyone told you on the day of your diagnosis.

Medical disclaimer

This post is for informational purposes only and is based on my personal experience and published scientific research. It does not replace medical advice. Don't change your treatment or dose, or start supplements, without consulting your doctor or endocrinologist, especially during pregnancy or while planning a pregnancy.

More in the Medical Disclaimer.

Sources

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• American Thyroid Association. Hashimoto's Thyroiditis (patient information). thyroid.org
• Cleveland Clinic. Thyroid Antibodies. clevelandclinic.org
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