Quick answer: Hashimoto's happens when genes that raise your risk meet a trigger. Documented triggers include too much iodine, certain infections, certain chemicals, and certain medications. Your genes set the risk. The trigger decides whether that risk turns into disease. For some people one trigger explains the case, for others it takes more than one.
Most people leave a Hashimoto's diagnosis with a prescription and no explanation for why it started. You are told your immune system is attacking your thyroid, and that you will likely take levothyroxine for life. What you are rarely told is why this started now, when other people carry the same risk genes and never get sick.
Genes alone do not explain why Hashimoto's starts. Something in your surroundings usually has to set it off. Research keeps pointing to the same pattern: it takes genes plus a trigger, not one or the other (a 2022 review of what drives the disease). That turns "why me" into a question you can look into.
Hashimoto's is one of the most common autoimmune thyroid diseases. It affects roughly 1 in 13 adults worldwide, around 7.5 percent, though estimates range widely by region and method (Hu et al., 2022). It is not rare, just well studied and poorly explained to patients.
One gets Hashimoto's. The other never does. Same risk genes, same years in the same surroundings. Certain genes, plus being female, make some immune systems more likely to turn on their own thyroid (StatPearls, NIH). That is why the disease runs in families and hits women far more than men. Risk also climbs with age.
Risk genes explain who is vulnerable. They do not explain who gets sick. Genetic risk works like a tipping point, not a life sentence, and an environmental exposure can tip it over. That is the part you can do something about.
A thyroid antibody test can be negative in someone who clearly has Hashimoto's, and positive in someone who doesn't. A single antibody number, high or low, does not settle it either way.
"Diagnosed with Hashimoto's" covers a wide range of people. Some have the antibodies and the autoimmune attack while their thyroid still keeps up. Others are further along, where the gland is starting to fall behind. Others have reached the point where it cannot keep up. Same diagnosis, very different starting points, which is part of why the trigger can differ so much from one person to the next.
How Hashimoto's is diagnosed is worth its own article. What antibody levels do and do not mean, why the test can read negative when the disease is real, and how the numbers move over time. we cover separately here.
Your thyroid hoards iodine. It runs a pump that pulls iodine out of your blood and concentrates it 20 to 40 times higher than your blood carries, because it needs iodine to make its hormones (Physiological Reviews). The catch is that the same greedy pump means whatever iodine you take in reaches the gland fast.
With iodine, the amount matters, and it matters differently depending on your risk. Too little is dangerous for anyone. For most of history, not enough iodine was a leading cause of thyroid disease worldwide, driving goiter and low thyroid function. In about 20 countries it still is (Iodine Global Network, 2025). But for someone at genetic risk, the other end of the scale is the problem. Too much iodine does not harm the average person's thyroid, but in someone at genetic risk, taking in too much can trigger Hashimoto's. That risk is about how much iodine a susceptible person takes in, not where they live. It shows up even in regions moving from too little iodine up to enough.
The research on iodine points the opposite way from what most thyroid supplements assume. Some functional medicine sources push high-dose iodine as a thyroid booster, but for people at genetic risk, taking in too much is a well-established trigger. The case rests on three kinds of study pointing the same direction, which is what makes it strong.
The first kind is population studies. The clearest example is a five-year study across three regions of China, published in the New England Journal of Medicine. As iodine intake climbed from mildly low to more than enough, autoimmune thyroiditis rose step by step, and people who already carried thyroid antibodies were the most likely to get worse (Teng et al., 2006). A 20-year follow-up of the same population confirmed the pattern held over time (Shan et al., 2023). Slovenia saw the same thing after raising iodine nationwide, with Hashimoto's cases climbing sharply (Slovenia follow-up, Croatian Medical Journal, 2011). This pattern has now shown up across many populations.
The second kind is laboratory studies, which show how it happens. Too much iodine appears to damage thyroid cells directly, not just show up alongside the disease. One 2023 study found that excess iodine triggers cell death in thyroid cells from Hashimoto's patients (Zhang et al., 2023). Other work links it to a second kind of cell damage in the same cells (Liu et al., 2019). Both are lab findings rather than proof in people, so they explain a plausible mechanism, not a settled cause.
The third kind is clinical studies in patients. In one small study, lowering iodine alone helped many patients with Hashimoto's-related low thyroid function get better, and those who started with more iodine in their urine improved the most (Yoon et al., 2003). A larger 2014 study in the journal Thyroid found the same in patients with early low thyroid function, and concluded lowering iodine could be a primary treatment option in iodine-rich countries (Joung et al., 2014). Japanese researchers first linked heavy seaweed intake to thyroid problems back in the 1960s. When population data, laboratory findings, and patient studies all point one way, the signal is hard to dismiss.
What we see in our own practice often goes beyond what these studies capture. When a patient who is genuinely taking in too much iodine commits to a personalized reduction and stays with it, often for many months, we often see thyroid antibodies fall and stay lower. Other physicians have reached out to us, surprised by results like these. It does not work for every patient, and it only works for those who were taking in too much to begin with, which is why the assessment below matters so much. For the right patient, this lever can matter more than anything else.
The same iodine change that helps one patient can harm the next. Some people are taking in too much without knowing it, and lowering it helps. Others are fine, or even low, and lowering it would do harm. There is no way to know which without looking at the individual, which is why we do not hand every Hashimoto's patient the same iodine advice. With each person we diagnose, we look closely at what they take in and where it comes from before changing anything.
Never lower iodine on your own, especially if you are pregnant, trying to get pregnant, or breastfeeding, when both too little and too much can affect thyroid health at a critical time. How to assess and adjust iodine safely is detailed enough for its own article. We are publishing one.
Your immune system can fight off an infection and then turn on your thyroid by mistake, because at a microscopic level the two look alike. This mix-up has a name: molecular mimicry (Frontiers in Cellular and Infection Microbiology, 2022).
One of the most-studied suspects is H. pylori, the bacteria known for causing stomach ulcers. Some studies have found it more often in people with Hashimoto's, while others have found no clear difference, so the case-control evidence is mixed and often falls short of statistical significance (case-control study, 2024). The idea is that H. pylori may resemble thyroid tissue closely enough to confuse the immune system. For now that link is a reasonable theory, not a proven one.
Epstein-Barr, the common virus that causes mononucleosis and stays in the body for life, is one of the better-studied infections linked to Hashimoto's. Researchers have found signs of the virus inside the thyroid tissue in about 4 out of 5 Hashimoto's patients in one study, and lab work shows how it could push immune cells to break their normal tolerance (Janegova et al., 2015). This is still an association rather than proof that the virus causes the disease.
In our own clinical experience, we have seen thyroid antibody levels drop in some patients once an active infection is treated. This is what we have observed in our own patients, not a controlled study, and results vary.
Pregnancy quiets the immune system on purpose, so the body does not treat the baby as a threat. After birth, the immune system switches back on, and in some women it swings too hard and turns on the thyroid. This is postpartum thyroiditis, and it affects roughly 5 to 8 percent of women in the year after giving birth, the most common thyroid problem tied to pregnancy (postpartum thyroiditis review).
It is essentially the same autoimmune attack as Hashimoto's, brought out by the immune reset of childbirth. One of the strongest warning signs is thyroid antibodies. A woman who already carries them, even with a thyroid that worked fine before, is at much higher risk after birth (StatPearls, NIH). It often runs a telltale course: a short overactive phase, then an underactive one, then recovery for many women, though some are left with a lasting underactive thyroid.
The trouble is that it looks exactly like new motherhood. Exhaustion, low mood, brain fog, and feeling off get written off as normal, so it goes missed constantly, sometimes for the whole first year. It may overlap with postpartum depression too, though the evidence on that link is mixed. If you had thyroid antibodies before pregnancy, or you feel far from yourself in the months after a baby, this is worth checking rather than pushing through.
You pick up trace chemicals from everyday plastics and receipts, and some of them have been linked to thyroid disease. Every plastic container, takeout box, pesticide, and store receipt you touch adds a little to your body's chemical load. A 2025 review found limited and inconsistent evidence that some, such as certain PCBs and pesticides, may be linked to autoimmune thyroid disease, drawing on only a handful of studies (systematic literature review, 2025). Heavy metals belong here too: a 2025 meta-analysis found lead in particular, along with cadmium, linked to thyroid disorders including Hashimoto's (heavy-metals meta-analysis, 2025).
How much any one exposure matters varies, and the evidence is mostly associational rather than proven cause and effect. For most people, chemical exposure is one contributing piece alongside iodine and infection. Whether a very heavy exposure could drive a case more strongly on its own is something the current research cannot rule in or out.
A few medical exposures round out the list of recognized triggers. Certain drugs, including lithium, the heart medication amiodarone, interferon, and newer cancer immunotherapy drugs, along with radiation to the neck, can all set off or worsen thyroid autoimmunity (StatPearls, NIH). These are less a part of everyday life, but they are one more reason your full medical history matters when the cause is not obvious.
Selenium is the nutrient with the clearest evidence behind it for Hashimoto's. It, vitamin D, and iron all keep coming up in the research, and none of them causes the disease, but low levels are common in people who have it, and correcting a real deficiency is worth doing.
A 2024 review of 35 randomized trials found selenium supplements lower thyroid antibodies. In patients not yet on thyroid medication, it also lowered TSH. It did not change thyroid hormone levels or reduce the need for medication (selenium meta-analysis, 2024). The likely reason it helps is that making thyroid hormone produces hydrogen peroxide, and selenium-dependent enzymes mop up that oxidative stress before it damages the gland. Vitamin D and iron are murkier. Both run low often in Hashimoto's, but it is not settled whether the low levels help cause the disease or are more a result of it (vitamin D review, 2025; Hu and Rayman, 2017). Iron matters mechanically too, since the enzyme that builds thyroid hormone depends on it.
None of the three is a cure, but checking your levels and correcting a genuine shortfall is worth doing. We go deeper on dosing, food sources, and the full evidence for each in our diet article.
Go looking for Hashimoto's advice online and you will be told to drop gluten and dairy within about five minutes. The evidence is thinner than the confidence behind that advice. We go deeper on eating for Hashimoto's in a separate article, so here is the short version.
For people without celiac disease, good trials do not show that going gluten-free reliably changes thyroid function, and across studies the effect on antibodies is inconsistent. One small pilot found a gluten-free diet lowered both thyroid antibodies, but it was a small, non-randomized study, so it does not settle the question (gluten-free pilot study, 2019). Autoimmune conditions do tend to travel together, and celiac disease shows up in people with Hashimoto's at roughly 1.5 to 2 times the usual rate (Roy et al., 2016), so testing for it makes sense. But that is different from the common claim that everyone with Hashimoto's should drop gluten. Dairy has even less behind it, with no strong trials showing that cutting it improves the disease.
What we think may be going on is a hypothesis. In the American diet, dairy is among the top iodine sources, and commercially baked bread adds iodine when it is made with iodate dough conditioners, which about one in five U.S. breads use (NIH Office of Dietary Supplements). Someone who drops both can cut a meaningful share of their iodine without meaning to. So when a patient feels better off gluten and dairy, it may reflect changes in iodine intake, but that has not been proven.
You will also see a lot about "leaky gut," the idea that a more permeable gut wall lets food and microbe particles through and keeps the immune system stirred up. Several studies have found signs of a more permeable gut in people with Hashimoto's (gut permeability study, 2021). It is also early, since the studies are small and show the two things happen together rather than proving one causes the other. In our practice, we look at gut health either way, because supporting the gut barrier can still be helpful. What we do not do is call it a proven cause.
Sometimes one trigger explains the whole disease. Sometimes it takes three at once. The iodine research above is the clearest example of the first, since fixing the excess can sometimes ease the disease with nothing else changed. Not every piece in this article applies to your case. The useful question is which ones do.
The investigation has to fit the patient, not a standard checklist. The same diagnosis can trace back to completely different causes from one person to the next. That is how our team works through every Hashimoto's case. We do not assume there is always more than one cause, and we do not assume iodine, infection, or any single thing is automatically the answer. We look at what is true for you.
The driver behind your Hashimoto's is usually findable, and finding it is the whole point. Indigo is a virtual clinic serving patients across the DMV, so this starts wherever you are. A complimentary Discovery Call is where every Indigo patient starts. It is a 20-minute phone call, and a team member walks through your symptom history, your past testing, and what you have already tried. You come away with a clear read on whether your case is one we can help with, and what a fuller workup would look for. No cost, no commitment, just a straight answer on whether this is worth pursuing.
This content is provided by Indigo Integrative Health Clinic for educational purposes only. It does not constitute medical advice, a diagnosis, or a treatment recommendation, and does not establish a provider-patient relationship. Individual health conditions vary — information presented here may not apply to your specific situation. Always consult a qualified, licensed healthcare provider before making decisions about your health, medications, supplements, or treatment plan.
Most people leave a Hashimoto's diagnosis with a prescription and no explanation for why it started. You are told your immune system is attacking your thyroid, and that you will likely take levothyroxine for life. What you are rarely told is why this started now, when other people carry the same risk genes and never get sick.
Scientists at MIT engineered mice that fight off Lyme and pass that protection to their pups. In a 2026 study, ticks that fed on these mice picked up almost no Lyme. It is a real step toward fewer infected ticks, but it does little for anyone who already has it.
A Lyme-literate evaluation starts with the sequence of symptoms, exposure history, and clinical pattern, not lab results alone. It is built to catch the cases the standard two-tier test misses, including the many patients who never recalled a tick bite. Across Washington, DC, Virginia, and Maryland, where both blacklegged and lone star ticks are established, we see these cases often.
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