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Hypothyroidism occurs when your thyroid gland doesn’t produce enough thyroid hormone, leading to symptoms of hypothyroidism such as fatigue, weight gain, depression, and brain fog. One of the essential diagnostic tools used to monitor thyroid function is a test that measures your levels of thyroid stimulating hormone (TSH), a pituitary hormone considered a marker for thyroid function.
The ultimate goal for hypothyroid patients is to optimize thyroid treatment. Optimal treatment means that your hypothyroid symptoms are significantly improved or even fully resolved, and your TSH and other thyroid hormone levels – as well as medication dosages – are stable over time.
When your underactive thyroid has been optimally treated for a while, it can come as a shock when a routine thyroid test panel shows that your TSH level has changed significantly or is falling outside the normal range. What’s going on? Why is your TSH level fluctuating? Ahead, a look at the factors that cause your TSH level to change when you’re being treated for hypothyroidism.
Certain medications and supplements can affect your TSH levels. These include:
- Dopamine agonists, commonly prescribed for Parkinson’s disease and certain pituitary disorders, can change TSH levels. These medications can suppress TSH secretion, leading to artificially low TSH levels.
- Corticosteroids, including prednisone, are frequently prescribed for their anti-inflammatory properties. However, these medications can interfere with the production and release of TSH, leading to increased TSH levels. The impact of corticosteroid drugs is more likely when you’re on longer-term treatment.
- Cholestyramine and colesevelam, commonly prescribed to lower cholesterol levels, can interfere with the absorption of thyroid hormones and raise TSH levels.
- Proton pump inhibitors (PPIs) are medications that reduce stomach acid production, often prescribed for conditions like acid reflux and gastroesophageal reflux disease (GERD). When taken with thyroid medication, PPIs can reduce the absorption of thyroid hormones and raise TSH levels.
- Furosemide, a diuretic commonly known as Lasix, treats conditions such as high blood pressure and edema (swelling). This medication can inhibit the absorption of thyroid hormones if taken at the same time as thyroid medication.
- Estrogen drugs such as oral contraceptives and hormone replacement therapy can interfere with the absorption of thyroid hormones.
- Lithium, prescribed as a mood stabilizer for people with bipolar disorder, can affect thyroid function and thyroid hormone production, worsening hypothyroidism and raising TSH levels.
- Calcium and iron supplements can interfere with the absorption of thyroid hormone replacement drugs, raising TSH levels.
- Antacids are taken for heartburn and indigestion symptoms. These medications contain aluminum and/or magnesium, which can bind with thyroid hormones and limit their absorption, causing TSH levels to rise.
Physical or emotional stress, as well as an acute illness or surgery, can impact the functioning of the thyroid gland and lead to changes in TSH levels. When you’re under stress, your adrenal gland can release high levels of the stress hormone cortisol. Cortisol can disrupt the feedback loop between the hypothalamus, pituitary gland, and thyroid, causing TSH levels to rise and worsening your thyroid condition.
People with autoimmune diseases can periodically have what’s known as an autoimmune flare. During a flare, your immune system becomes overactive, and antibodies can increase. The increased inflammation can interfere with thyroid function and cause your thyroid antibody and TSH levels to rise.
Fluctuations in your body weight can affect your TSH levels. When you gain weight, you may need an increased dosage of thyroid hormone replacement medication, or you can experience increases in your TSH level. Similarly, weight loss often reduces your optimal dosage and can cause TSH to become too low.
When you’re hypothyroid during cold weather, your TSH may rise somewhat compared to warmer months. The need for a higher dose of thyroid medication in colder weather is due to the body’s increased demand for heat generation.
How your thyroid function test results are handled and stored can, in some cases, affect the integrity of the test results. For example, blood samples for thyroid lab tests should not be exposed to high temperatures, as the heat can cause the sample to degrade, affecting the accuracy of the TSH test result. Many thyroid patients have reported inaccurate TSH test results when blood samples were stored in lab pickup boxes outdoors or transported in vehicles during hot weather.
TSH levels can change throughout the day, and levels are typically lowest in the morning and higher in the evening. Some hypothyroid patients have even reported changes of 3 to 5 points in TSH levels when comparing blood test samples taken in the morning and late afternoon of the same day.
When you’re on levothyroxine treatment – the synthetic form of thyroxine (T4) – you need to be aware that the potency of each brand or manufacturer can range from 95 to 105% of the stated dosage. So when you get a refill of generic levothyroxine, or you switch brands, your new medication refill can vary in potency by as much as 10 percent. These potency variations can cause significant changes in your TSH level.
Thyroid medications are regularly tested for potency, and periodically, batches of thyroid medication are identified as sub-potent or super-potent. This means that at your usual dosage, your medication is less effective, which can cause an increase in your TSH level. Similarly, a super-potent medication can result in a TSH level that’s too low.
If you have started or stopped a high-fiber or gluten-free diet since your last TSH test, this change can significantly affect your TSH and thyroid hormone levels.
Also, if you have started or stopped drinking coffee within an hour of taking your thyroid medication, this can also significantly affect your TSH levels.
If you have developed a gastrointestinal illness that affects the absorption of your thyroid medication, this can worsen your hypothyroidism and cause your TSH level to increase. Gastrointestinal diseases that can affect the absorption of thyroid medication include:
- Celiac disease
- Non-celiac gluten intolerance
- Inflammatory bowel disease
- Crohn’s disease
- Ulcerative colitis
- Helicobacter pylori (H. pylori) infection
- Gastroesophageal reflux disease (GERD)
- Atrophic gastritis
Changes to your estrogen levels can affect thyroid function. Specifically, higher estrogen levels –or estrogen dominance during perimenopause and menopause – can signal the liver to increase the production of thyroid-binding globulin (TBG), which binds to thyroid hormone, reducing the amount of thyroid hormone available and increasing TSH levels.
There are a few things to keep in mind to help minimize changes in TSH levels.
First, make sure you take your thyroid medication correctly. Ideally, that means taking it on an empty stomach, first thing in the morning, an hour or more before eating or drinking coffee. Medications and supplements -- especially those containing iron or calcium -- should be taken at least three to four hours apart from thyroid medication. For more guidelines, read How and When to Take Thyroid Medication.
Also, if you have gastrointestinal illness or absorption problems, consider the liquid form of levothyroxine (Tirosint-SOL), which is better absorbed than tablet forms.
Finally, monitoring your TSH and other key thyroid levels with blood tests is essential to your hypothyroidism treatment and overall thyroid health. To make it simple and convenient, consider using Paloma’s Complete Thyroid Blood Test Kit, which lets you test your levels of thyroid hormone -- including TSH, Free T4, Free T3, and Thyroid Peroxidase antibodies -- easily from home using painless blood spot thyroid testing.