This article is written by mr.hotsia, a curious traveler who has spent years exploring Thailand, Laos, Vietnam, Cambodia, Myanmar, India and many other Asian countries. In border clinics, mountain hospitals and city labs, I often see the same scene.
Someone holds a paper that says “TSH high” or “hypothyroidism.”
They look at me and ask
“Why did my thyroid slow down? What actually causes hypothyroidism?”
The honest answer is:
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There is no single cause.
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Some causes are inside the body, like autoimmune disease and genetics.
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Some are from medical treatment, such as surgery or radioiodine.
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A few are related to nutrition, medicines or temporary inflammation.
Let us walk through the main causes, calmly and clearly.
What is the basic idea behind hypothyroidism?
Your thyroid is a small gland in the neck that makes hormones which help control:
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Energy use
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Body temperature
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Heart rate
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Digestion
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Brain and muscle activity
Hypothyroidism happens when
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The thyroid does not make enough hormone for what the body needs.
This can happen because
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The gland itself is damaged or under attack
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The gland has been removed or treated
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The brain signals to the gland are disturbed
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The gland is temporarily inflamed and becomes “tired” for a while
Different causes, same final result: not enough thyroid hormone.
1. Autoimmune thyroid disease (Hashimoto’s)
In many countries I visit, the most common cause of long term hypothyroidism is autoimmune thyroiditis, often called Hashimoto’s.
In this condition
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The immune system, which usually defends the body, mistakenly attacks the thyroid.
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Over time, this slow “friendly fire” can damage thyroid cells.
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The gland gradually loses its ability to produce enough hormone.
Features often seen:
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It can run in families with other autoimmune conditions.
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It is more common in women than men.
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It may progress slowly over years, so symptoms creep in gently.
You do not cause Hashimoto’s by eating one wrong food or having one stressful day. It is usually a mix of genetics and environmental triggers that science is still learning about.
2. Thyroid surgery and radioiodine treatment
As I travel, I meet people whose thyroid story began with another thyroid problem. For example:
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An overactive thyroid
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A large goiter pressing on the throat
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Suspicious nodules or thyroid cancer
To treat those conditions, doctors may
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Remove part or all of the thyroid gland (thyroid surgery)
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Use radioactive iodine to shrink or destroy overactive tissue
These treatments can be very important and even lifesaving.
However, after them
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The remaining thyroid tissue may not produce enough hormone.
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Hypothyroidism then appears as an expected consequence.
In these cases, hypothyroidism is not a mistake, it is a known result of necessary treatment, and lifelong thyroid hormone replacement usually becomes part of daily life.
3. Medications that affect the thyroid
In clinics across Thailand, Laos, Vietnam, Cambodia, Myanmar and India, I sometimes see people whose thyroid slowed down while using certain medicines.
Some examples of drugs that can affect thyroid function include
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Certain heart medicines
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Some mood stabilisers
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Some cancer or immune system treatments
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Very high iodine containing drugs in special cases
These medicines are often important for serious conditions, so they cannot simply be stopped on your own. In some people they may
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Reduce hormone production
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Trigger thyroid inflammation
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Unmask a tendency to thyroid disease that was already present
When this happens, doctors may adjust the medicine, add thyroid monitoring or start thyroid hormone replacement if necessary.
4. Iodine imbalance: too little or too much
In border markets I see two extremes
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Places where people use little or no iodised salt
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Places where seaweed snacks and iodine supplements are very popular
The thyroid needs iodine to produce hormone, but balance is important.
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Too little iodine
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Can cause an enlarged thyroid (goiter)
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May reduce hormone production in areas with serious deficiency
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Too much iodine
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Can stress the thyroid in sensitive people
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Sometimes triggers underactivity or overactivity
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That is why many health systems recommend
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Using iodised salt in normal amounts
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Avoiding very high dose iodine supplements unless prescribed
Iodine balance supports thyroid health, but it does not prevent all types of hypothyroidism, especially autoimmune forms.
5. Thyroiditis: inflammation of the thyroid
Thyroiditis means inflammation of the thyroid gland. Along dusty roads and river clinics, I hear different stories of thyroiditis that can lead to temporary or sometimes lasting hypothyroidism, such as
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Subacute thyroiditis
Often after a viral infection, with neck pain and tenderness. The gland may first leak extra hormone (causing temporary hyperthyroid symptoms), then become underactive for a while before recovering. -
Painless or “silent” thyroiditis
Inflammation without much pain. It can also cause a phase of high hormone, followed by low hormone. -
Postpartum thyroiditis
This happens in some women after pregnancy. The thyroid may swing from overactive to underactive within the first months after giving birth. Many recover, but some remain hypothyroid.
Thyroiditis does not always cause permanent damage. In some people the gland recovers, in others it remains underactive and needs long term support.
6. Problems in the pituitary or hypothalamus
Usually, the brain tells the thyroid what to do by sending TSH from the pituitary gland.
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If the pituitary or a nearby structure called the hypothalamus is damaged by
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Tumours
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Surgery
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Radiation
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Severe injury
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then it may not send enough TSH.
The thyroid itself might be able to work, but it is not being asked to.
This is called secondary or tertiary hypothyroidism.
It is less common than primary thyroid problems, but it is an important cause and is managed differently, because more than one hormone system might be affected.
7. Congenital hypothyroidism (present at birth)
In some newborn babies, the thyroid does not develop or function properly. This is known as congenital hypothyroidism.
Causes can include
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The gland missing or very small
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The gland in an abnormal position
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Genetic or developmental problems that affect function
Many countries check newborns with a heel prick blood test to find this early, because early thyroid hormone treatment may support normal growth and brain development.
This type of hypothyroidism is not caused by anything the baby did. It is a development issue that needs early recognition and ongoing care.
8. Aging and “wear and tear”
In older adults I meet on trains and in temple courtyards, thyroid function sometimes changes without a single dramatic cause.
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The immune system changes with age
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The thyroid gland may become less efficient
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Mild hypothyroidism or “borderline” thyroid tests can appear
In some older people, doctors may
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Choose active treatment if symptoms or risks are present
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Or watch carefully with repeat tests if changes are mild
So aging itself can be associated with thyroid slowing, although it is not exactly a “cause” like surgery or strong medication.
9. Can lifestyle alone cause hypothyroidism?
People often ask me in markets and food stalls
“Did I cause this by eating wrongly or sleeping badly?”
The simple answer is
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Normal lifestyle choices rarely cause true hypothyroidism by themselves.
However
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A severely restricted diet without iodised salt or seafood in an area of natural iodine deficiency can contribute to thyroid problems.
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Extreme low calorie crash diets and repeated harsh fasting may confuse hormonal systems, although they usually cause temporary adaptation rather than permanent gland failure.
So lifestyle may influence thyroid comfort and symptom levels, but it is usually not the core cause of primary hypothyroidism, especially when autoimmune disease is involved.
10. Why do some people develop hypothyroidism while others do not?
Across Thailand, Laos, Vietnam, Cambodia, Myanmar, India and many other places, I see families where
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One sister has Hashimoto’s
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Another sister has no thyroid trouble at all
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A cousin has another autoimmune disease
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Parents or grandparents had “goiter” or thyroid problems
This suggests that
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Genetics provide a base level of risk.
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Environment and life events act as triggers.
Factors that may play some role include
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Family history of thyroid or autoimmune disease
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Female sex
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Certain infections or strong stressors
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Iodine imbalance
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Some medications or treatments
Science cannot yet predict exactly who will develop hypothyroidism. It is usually a combination of several influences, not one simple mistake.
FAQs: What causes hypothyroidism?
1. What is the most common cause of hypothyroidism?
One of the most common causes is autoimmune thyroid disease, often called Hashimoto’s thyroiditis, where the immune system slowly damages the thyroid gland.
2. Can thyroid surgery cause hypothyroidism?
Yes. If part or all of the thyroid is removed for nodules, cancer or an overactive gland, the remaining tissue may not produce enough hormone and long term replacement is often needed.
3. Does radioactive iodine treatment lead to hypothyroidism?
It can. Radioiodine is used to treat overactive thyroid or some cancers and often results in an underactive thyroid later, which is then managed with thyroid hormone tablets.
4. Can medicines cause an underactive thyroid?
Some heart drugs, mood stabilisers, cancer therapies and iodine rich medicines can affect the thyroid in certain people. Your doctor usually monitors thyroid function if you use these long term.
5. Is lack of iodine still a cause of hypothyroidism today?
Severe iodine deficiency can cause thyroid problems, especially in areas without iodised salt. In many countries, iodised salt has reduced this risk, but both too little and too much iodine can still stress the gland.
6. What is thyroiditis and how does it cause hypothyroidism?
Thyroiditis is inflammation of the thyroid. It can happen after infections, pregnancy or for unknown reasons. The gland may leak hormone and then become underactive for a while. Some people recover, others remain hypothyroid.
7. Can problems in the brain cause hypothyroidism?
Yes. If the pituitary or hypothalamus does not send enough TSH, the thyroid may not be properly stimulated. This is called secondary or tertiary hypothyroidism and is less common.
8. Are babies ever born with hypothyroidism?
Yes. Some babies have congenital hypothyroidism because their thyroid did not form or function normally. Newborn screening often detects this early so treatment can begin soon.
9. Did I cause my hypothyroidism through bad lifestyle choices?
Normal everyday habits do not usually cause hypothyroidism. Autoimmune disease, medical treatments, genetics and other factors are much more important. Lifestyle still matters for how you feel and how you manage the condition.
10. What is the simplest way to think about the causes of hypothyroidism?
Think of hypothyroidism as a final result where the thyroid does not make enough hormone. Many roads can lead there: immune attacks, surgery, radioiodine, medicines, iodine imbalance, brain signalling problems or birth defects. You rarely cause it alone with daily habits, but you can support your health and treatment through the choices you make from today onward.
I’m Mr.Hotsia, sharing 30 years of travel experiences with readers worldwide. This review is based on my personal journey and what I’ve learned along the way. Learn more |