Thyroid-stimulating hormone (TSH) is an important hormone that is considered to be the “master controller” of your thyroid. It is linked to a wide variety of health conditions, and its effects can be either beneficial or negative depending on your age. Read on to find out how TSH works, what can impact TSH levels in your body, and how it all relates to your health.
What is Thyroid-Stimulating Hormone (TSH)?
Thyroid-stimulating hormone (TSH), also known as thyrotropin or thyrotrophin, is made by the pituitary gland and secreted into the bloodstream. The main purpose of TSH is to stimulate the thyroid gland into producing the hormones T3 (triiodothyronine) and T4 (thyroxine) [1, 2, 1].
The thyroid gland is located at the base of your neck, below the Adam’s apple. It absorbs iodine from the blood to produce the T3 and T4 hormones. The thyroid is important because the T3 and T4 hormones it makes play a significant role in the function of almost every part of the body, including the brain, heart, and liver .
Thyroid activity is controlled by the hypothalamus, which produces thyrotropin-releasing hormone (TRH) to tell the pituitary gland to make TSH, thereby causing the thyroid to produce more T3 and T4 when levels are low. If T3 and T4 levels are high, the hypothalamus reduces TRH production and thus, less TSH is made. This process helps keep T3 and T4 at the appropriate levels .
How TSH Works
The thyroid-stimulating hormone increases T3 and T4 levels in several different ways.
TSH stimulates the production of T3 and T4 by binding to TSH receptors (TSH-R) on the thyroid gland, where it helps the thyroid gland make more proteins that absorb iodine from the bloodstream. The thyroid then uses this iodine to make more T3 and T4 [5, 6].
Iodine can exist in different forms, and it can only be used to make T3 or T4 if it’s in the active form (oxidized). For this reason, TSH further boosts T3 and T4 production by increasing the protein that converts iodine into its active form (thyroid peroxidase) [7, 8].
Thyroid-stimulating hormone not only increases T3 and T4 production, but it also stimulates their release into the bloodstream. When T3 and T4 are made, they are stored by binding with another protein (thyroglobulin), which keeps them from entering the bloodstream. TSH helps break down this protein (by increasing proteases), which allows T3 and T4 to be released [7, 9].
Health Risks of High TSH
1) Poor Heart Health
2) High Fat and Cholesterol Levels
Another study with almost 21,000 people showed similar results, and also found that higher TSH levels are correlated with lower levels of “good” cholesterol (high-density lipoproteins, or “HDL”) .
Two separate studies have shown that among women, overweight and obese patients have higher TSH levels than normal-weight patients. This includes people with higher overall body weight and body mass index (BMI), larger waist size, and higher body fat percentage [17, 18].
Another study found that, compared to women with low TSH levels, healthy young women with high TSH levels were found to be twice as likely to have metabolic syndrome (a condition that causes obesity, high blood pressure, and high levels of sugar, fat, and cholesterol in the blood) .
The link between TSH and obesity doesn’t apply only to women, either: two large-scale studies have shown that higher TSH levels are associated with a higher BMI in both male and female patients alike [20, 21].
TSH is involved in the weight of children as well. Obese and overweight children have higher TSH levels, and these high levels are linked to increases in cholesterol, fat, and blood pressure .
4) Pregnancy Issues
Levothyroxine is a drug used to treat thyroid problems and is more commonly given during pregnancy. One study looked at 1,013 women treated with Levothyroxine and found that many of them had increased TSH levels, which was associated with an increased risk of miscarriage .
In a study with over 184,000 women, mothers with high TSH levels 6 months before conceiving had an increased likelihood of spontaneous abortion (miscarriage before 20 weeks), stillbirth, premature birth, and other delivery-related issues .
Patients given 0.9 mg of TSH for 2 days had impaired blood vessel function, which was possibly due to inflammation and oxidative stress (study with 24 women) .
6) Thyroid Cancer
Another study showed that for 126 patients with a specific type of thyroid cancer (papillary thyroid microcarcinoma), high TSH levels were correlated with faster cancer progression .
In a study of 54 healthy young adults, higher levels of TSH were associated with higher levels of the stress hormone cortisol, suggesting that TSH may make the body more sensitive to the effects of stress .
Health Risks of Low TSH
1) Linked With Worse Mental Health
Low TSH levels may contribute to declines in mental health among the elderly.
In a study with 293 adults over the age of 65, low TSH levels were linked with deteriorating cognitive function .
2) Linked to Worse Bone Health
Having higher TSH levels may also protect bone health in the elderly.
In a study with 686 elderly women, those with low TSH levels had a much higher risk of fracturing their hip bones or spinal cord .
A study with over 14,000 patients showed that elderly women (but not elderly men) with low TSH levels had a higher likelihood of hip fractures .
TSH and the Elderly
However, although high levels of TSH are generally associated with negative outcomes in adults and children, this might not be the case for the elderly. In fact, many studies suggest the opposite – that in older people, it is actually lower TSH levels that cause problems, while higher levels may be protective.
A number of findings suggest that high TSH levels may be beneficial for living longer.
A very elderly group of people (with a median age of 98) had significantly higher levels of TSH when compared to a control group with a median age of 72 .
For 2,290 elderly adults aged 70-79, those with slightly elevated TSH levels had less difficulty walking, were able to walk faster, and were in better shape than those with normal TSH levels .
A study with 558 adults from ages 85 to 89 found that those with the highest TSH levels had the lowest overall risk of dying .
Causes and Symptoms of Low TSH & Hyperthyroidism
Hyperthyroidism is a condition where the thyroid is overactive and produces excess thyroid hormones T3 and T4. Because thyroid hormones are involved in so many different parts of the body, this can cause a wide variety of symptoms.
Causes of Hyperthyroidism
Other common causes of hyperthyroidism are toxic nodular goiters (swollen thyroid — also known as Plummer’s disease) and painless (or “silent”) thyroiditis (a condition where the immune system attacks the thyroid gland, causing it to become inflamed) .
Symptoms of Hyperthyroidism
A study of 84 hyperthyroidism patients found that the most common symptoms include :
- Increased sweating
- Extreme thirst
- Hyperactive reflexes
- Heat intolerance
- Muscle weakness
- Sleep difficulties
- Weight loss
- Increased eye sensitivity, leading to crying or tearing up, or painful sensitivity to light (photophobia)
- Increased heart rate (tachycardia)
- Swelling of tissues (peripheral edema)
- “Lid lag” (delay in the movement of eyelids)
- Excess stool production (more than 3x/day)
Hyperthyroidism can also cause psychological symptoms such as apathy, although this was found to be more common in elderly patients (> 70 years old) .
Hyperthyroidism can also cause a number of symptoms that affect the mouth, jaw, and throat, such as burning mouth syndrome, osteoporosis of jaw bones, swollen or enlarged thyroid tissue (goiter), and higher chance to develop cavities and periodontal disease .
Causes and Symptoms of High TSH & Hypothyroidism
Hypothyroidism – the opposite of hyperthyroidism – is when the thyroid is underactive and doesn’t produce enough T3 and T4 hormones. Because thyroid hormones are involved in so many different parts of the body, this can cause a wide variety of symptoms.
Causes of Hypothyroidism
Treatments that kill or surgically remove thyroid cells, such as radioiodine ablation and thyroidectomy, can also cause hypothyroidism .
Symptoms of Hypothyroidism
Hypothyroidism causes a variety of physical and psychological symptoms.
The most common symptoms are:
- Fatigue 
- Constipation 
- Weight gain 
- Carpal tunnel syndrome 
- Depression 
- Anxiety 
- Memory problems [70, 71, 72]
- Attention issues 
Hypothyroidism may also cause a number of symptoms that affect the mouth, such as mouth breathing, thick lips, small jaw (micrognathia), thin tooth enamel (enamel hypoplasia), tongue swelling or inflammation, enlarged salivary glands, distorted sensations of taste (dysgeusia), and more .
Other symptoms of hypothyroidism can include :
- Low heart rate
- Reduced sweating
- Shortness of breath
- Hair loss
- Dry or yellow skin color
- Hoarse voice
- Skin swelling
- Hearing problems
- Muscle or joint pain
- Slow reflexes
- Menstrual cycle problems like heavy bleeding
- Decreased fertility
- Erectile dysfunction
Causes of High or Low TSH
There are many different ways that stress can impact your T3 and T4 levels.
For example, many studies have suggested that experiencing negative and stressful life events increases the likelihood of developing Graves’ disease, a common cause of hyperthyroidism [79, 80, 81, 82, 83].
Nonetheless, several animal studies support the idea that stress is a contributing factor in thyroid dysfunction. For example, multiple rat studies have found that stress disrupts thyroid function, although in different ways.
Stress-induced by electric shocks to rat tails led to decreases in T3, T4, and TSH .
Hypothyroidism was induced in rats who were exposed to social stress .
Going on a ketogenic diet (high-fat, low-carb) is popular with many people, and is even a common treatment for people with epilepsy. However, the ketogenic diet can interfere with thyroid function. For example, a study of 120 epilepsy patients found that 17% developed hypothyroidism as a result of this diet .
Another study showed that a high-fat low-carb diet also can decrease T3 levels, and both high-fat low-carb and high protein low carb diets can lower TSH levels .
Overeating is another common cause of thyroid dysfunction. A study found that chronic overeating led to an increase in T3 levels over both the short- and long-term (from 3 weeks up to 7 months) .
A common treatment for cancer itself is radiation therapy. Unfortunately, radiation therapy puts patients at a greater risk for thyroid cancer, as seen in multiple studies involving children [96, 97, 98].
Three months of increased soy intake led to goiters, sleepiness, and constipation in a study involving 37 previously-healthy adults. However, the symptoms went away after stopping excess soybean intake .
In a study with 78 patients, infants with hypothyroidism who were fed soy formula had higher TSH levels than infants fed formula without soy .
Thyroid hormones are made from the chemical iodine, which humans need to get from the food they eat. Not getting enough iodine in your diet (severe iodine deficiency) can lead to hypothyroidism, and may even cause goiters (a large swelling of the thyroid gland that bulges out from the neck) [107, 108].
For example, children living in an area with abnormally high iodine concentrations in their drinking water show higher rates of thyroid dysfunction (increased levels of TSH and thyroid antibodies) .
Another study with 60 people showed that vitamin D deficiency is also associated with hypothyroidism .
Goiters are an enlargement of the thyroid gland, and can sometimes be seen as a bulging in the neck area. Goiters are usually a sign of thyroid dysfunction or iodine deficiency .
Conditions That Increase Risk of Thyroid Problems
Diabetes and Thyroid Dysfunction
Diabetes is strongly related to thyroid dysfunction – especially hypothyroidism – which can greatly influence your T3 and T4 levels.
Biological signs of low thyroid activity (such as high TSH and low T4 levels in the blood) correlate with an increased risk for diabetes .
Other studies have reported that up to 30% of diabetic patients may have some type of abnormal thyroid functioning .
Because of the hormonal changes and thyroid stimulation that occur during pregnancy, thyroid dysfunction is more common in pregnant women. About 2.1 – 3.4% of pregnant women experience either hypothyroidism or hyperthyroidism .
One study with 482 hypothyroid pregnant women showed that if these thyroid problems are treated, there is no increased risk to their children. However, the mothers still have an increased likelihood of developing high blood pressure and liver and kidney damage (preeclampsia) .
However, pregnancy-related thyroid problems can cause developmental issues in children if left untreated. The children of 62 women who had hypothyroidism performed worse on a variety of tests that measured their intelligence (IQ), attention, language and reading skills, and performance in school .
Many other studies have also found a variety of adverse effects on the children of women with hyperthyroidism. These include low baby weight during pregnancy (intrauterine growth restriction), premature labor and birth, and low birth weight [138, 139, 140].
Polycystic Ovary Syndrome (PCOS)
Women with polycystic ovary syndrome (PCOS) are more likely to experience thyroid dysfunction and signs of hypothyroidism such as autoimmune thyroiditis (like Hashimoto’s disease), high TSH levels, and goiters. Hypothyroidism can cause ovarian cysts to develop but is unlikely to cause PCOS itself [141, 142, 143].
TSH Blood Test
It may sound counterintuitive, but high TSH levels can indicate an underactive thyroid, while low TSH levels can indicate an overactive thyroid. This is because when you have an underactive thyroid the thyroid hormones T3 and T4 are low, and so the body responds by increasing TSH to stimulate T3 and T4 production. The opposite happens in the case of an overactive thyroid.
The timing of the TSH test can make a difference in the results because your TSH levels change naturally throughout the day (following a circadian rhythm). Studies show that TSH levels are highest at night and lowest during the afternoon [147, 148, 149, 150].
However, looking at TSH levels alone can result in a misdiagnosis. A thyroid panel that includes T4 (free T4) and T3 (free or total T3) levels can be ordered for a more complete and accurate picture .
How To Treat Thyroid Issues
Natural Ways to Help with Thyroid Issues
If you are lactose intolerant, restricting lactose intake may help thyroid functioning. One study with 83 patients with Hashimoto’s thyroiditis showed that a lactose-free diet led to decreased TSH levels for patients with lactose intolerance .
The herbal medicine ashwagandha can also help with thyroid issues. One study with 50 people showed that patients with mild hypothyroidism who took Ashwagandha had improved levels of TSH, T3, and T4 compared to placebo .
The most common treatment for hyperthyroidism in the United States is radioiodine ablation, which is generally safe. Radioactive iodine destroys thyroid cells, and therefore fewer thyroid hormones are produced [49, 160].
Other treatment options for hyperthyroidism include thyroidectomy (surgical removal of the thyroid), and “antithyroid” medications such as Tapazole (methimazole) and propylthiouracil (which stop thyroid hormone synthesis) or cholestyramine (which promotes excretion of excess thyroid hormones) [49, 160].
Other treatments that also increase the level of thyroid hormones include dried thyroid extract (thyroid tissue taken from animals and prepared for medical use) and liothyronine (L-T3). Studies show that these options can be effective as well, with some patients preferring dried thyroid to Levothyroxine [162, 163, 164].
Side Effects of TSH Treatments
One study with 449 Graves’ disease patients showed that side-effects of antithyroid medications include skin rashes, liver damage (hepatotoxicity), and low white blood cell count (agranulocytosis/neutropenia) .
Other side-effects of antithyroid medications are joint pain, swelling, nausea, and vomiting .
One study with 30 hypothyroid patients showed that levothyroxine can lead to impaired diastolic function (filling of the heart with blood), lower exercise capacity, and increased the thickness of artery walls .
Thyroid-Stimulating Hormone Interactions
One study with 20 healthy adults showed that blocking dopamine receptors led to increased TSH levels, further indicating that dopamine inhibits TSH .
One rat study showed that administering norepinephrine can lead to increased TSH levels .
Antidepressant medications can have different effects on TSH depending on what type they are.
One study with 62 depressed patients showed that the norepinephrine reuptake inhibitor (NRI) reboxetine reduced TSH. However, the selective serotonin reuptake inhibitor (SSRI) sertraline increased TSH, suggesting that NRIs and SSRIs affect TSH differently .
One study with 19 depressed patients treated with SSRIs showed a relationship between TSH levels and symptom improvement. Patients with lower levels of TSH prior to treatment had greater improvements in their depressive symptoms .
Studies have shown that glucocorticoids (steroid hormones such as cortisol and dexamethasone) lower TSH levels in both hypothyroid patients and healthy people (potentially by inhibiting TRH) [182, 183, 184, 185].
Rexinoids (a type of retinoid) may lower thyroid-stimulating hormone levels in rodents, healthy people and cancer patients (possibly by inhibiting TSH secretion and gene expression) [190, 191, 192, 193, 194].
However, one study with 10 patients showed that one type of rexinoid (bexarotene) did not affect TSH levels .
A meta-analysis of 7 different studies showed that metformin reduces TSH levels for hypothyroid patients, but not for people with normal thyroid function .
Clonidine, an alpha-adrenergic agonist, increased TSH levels .
One study with 38 cancer patients showed that after chemotherapy with drugs such as docetaxel, TSH levels rose significantly .
One study with 70 school children showed that those living in areas with excess fluoride in the water had higher levels of TSH .
One study found that smokers have lower TSH levels than non-smokers .
Natural Sources of Thyroid Hormones
Natural or dried thyroid extracts (thyroid tissue is taken from animals and prepared for medical use) are available as a natural source of thyroid hormones, which is helpful for people with hypothyroidism .
Limitations and Caveats
A lot of studies in this article talk about associations between high or low levels of TSH and certain conditions. These studies are relevant but it is important to note that correlation does not imply causation. Just because abnormal TSH levels are linked to specific conditions it does not mean that TSH caused these conditions. It could be the case that the disease caused the abnormal TSH levels, or some underlying factor caused both. Without further studies, it’s impossible to know which is the case.
Common drugs to help with thyroid function include levothyroxine (for hypothyroidism) and antithyroid medication like methimazole (for hyperthyroidism). Here are some positive and negative reviews from the web for each.
- One user with Hashimoto’s disease from an early age stated that levothyroxine helped with losing weight, decreasing irritability, and increased concentration.
- Another person with Hashimoto’s disease said that it lowered their TSH and helped them feel great and full of energy.
- One user with underactive thyroid said that it helped combat feelings of being cold and fatigued.
- One user with hypothyroidism felt that it made them feel much more energetic and active.
- One user with hypothyroidism listed many negative side-effects such as headaches, insomnia, and feeling depressed.
- One user with Hashimoto’s disease said that after using levothyroxine they felt much more inflammation and that it went away after stopping levothyroxine.
- One person with underactive thyroid said that levothyroxine caused lip swelling and irritation and so they stopped taking it.
- One person with hyperthyroidism said that they experienced some side-effects like weight gain but that it has greatly helped with tremors and palpitations.
- One user with Graves’ disease said that methimazole alleviated a variety of symptoms including tremors, severe muscle weakness, and emotional instability.
- One person with hyperthyroidism said that methimazole allowed them to feel normal again very quickly without any side-effects.
- One user with hyperthyroidism complained of symptoms similar to an allergic reaction with itchy skin, toothaches, and rashes.
- Another user with hyperthyroidism said the drug gave them terrible diarrhea, headaches, nausea, and hair loss.
- One person with Graves’ disease said that although it started out positively, they began to experience serious side-effects like fast heart rate and kidney problems.
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