Borderline Hypothyroidism: Symptoms, Treatment and More
Subclinical, or “borderline,” hypothyroidism is an early form of hypothyroidism. This condition causes an underactive thyroid, which results in high thyroid-stimulating hormone (TSH) levels. People with borderline hypothyroidism often do not have symptoms. A healthcare provider can monitor your TSH levels and advise treatment if necessary.
A healthcare provider can diagnose borderline hypothyroidism using a blood test to check TSH levels. They may recommend medication to aid thyroid function. Not everyone with a mild underactive thyroid will need treatment.
Borderline hypothyroidism affects as many as 15% of people. Read on to learn what borderline hypothyroidism is, if it causes symptoms, and whether it should be treated.
Your thyroid gland governs much of the metabolic activity in your body. An underactive thyroid, meaning it’s not producing enough thyroid hormone, can cause symptoms like:
- Constipation or passing hard stools
- Depression
- Fatigue or weakness
- Feeling cold
- Hair thinning or brittle fingernails
- Joint or muscle pain
- Menstrual periods that are heavier and more irregular than normal
- Pale or dry skin
- Weight gain
Borderline hypothyroidism can be so minor that there are only very mild, non-specific symptoms or none at all. Most cases are asymptomatic, meaning no symptoms. This subclinical form increases a person’s chances of hypothyroidism symptoms later in life.
The pituitary gland in the brain secretes TSH. This hormone sends signals to the thyroid to create the hormones triiodothyronine (T3) and thyroxine (T4). The thyroid is a butterfly-shaped gland in the center of the neck.
The brain releases more TSH in an effort to increase levels when you have an underactive thyroid. Borderline hypothyroidism happens if TSH levels are higher than normal but T3 and T4 levels are normal.
Hypothyroidism is most commonly caused by thyroiditis, or inflammation of the thyroid. Thyroiditis damages the cells in the thyroid, negatively affecting hormone production. Autoimmune disorders, pregnancy, and viral infections can result in thyroiditis.
Risk Factors
Risk factors that increase the likelihood that you develop borderline hypothyroidism include:
- A family history of thyroid disease
- A personal history of preterm delivery, miscarriage, or infertility
- Amiodarone or lithium use
- Autoimmune disorders, such as type 1 diabetes
- Having thyroid antibodies
- Iodine deficiency
- Obesity
- Older age
- Radiation exposure to the head or neck
You may visit an endocrinologist, or a healthcare provider who specializes in hormone disorders, to diagnose borderline hypothyroidism. They will ask about your health history and perform a physical exam. The endocrinologist can feel the thyroid to see if it’s smaller than usual.
The endocrinologist will also order a blood test to measure the levels of two hormones: T4 and TSH. High levels of TSH, or above 4.0 to 4.5 milli-international units per liter (mIU/L), can indicate an underactive thyroid. T4 levels will be relatively normal in the case of borderline hypothyroidism.
This blood test can usually confirm borderline hypothyroidism. Other diagnostic tests are likely not necessary but can include:
- Thyroid peroxidase (TPO) antibody test: The presence of these antibodies can indicate that an autoimmune disorder is the cause of an underactive thyroid.
- Thyroid ultrasonography: This imaging test creates detailed pictures of the thyroid.
- Other blood tests: Hypothyroidism can increase the risk of heart disease. A healthcare provider may want to perform a complete blood count (CBC) and check your cholesterol and sodium levels. These blood tests can look for indicators of heart disease.
The goal of treatment is to closely replicate normal thyroid functioning. You’ll need to take medication to replace the amount of thyroid hormone the gland can’t make if you have hypothyroidism. Thyroid hormone is available as levothyroxine, which is biologically equivalent to T4. Levothyroxine is most commonly prescribed in tablet form but is also available in gel capsule or liquid forms.
The American Thyroid Association (ATA) guidelines recommend levothyroxine therapy at TSH levels of 10 mIU/L or less if you meet any of the following criteria:
- There are clear symptoms of hypothyroidism
- There’s evidence of atherosclerotic heart disease (hardening of the arteries) or heart failure
- You have positive thyroid autoantibodies
Borderline hypothyroidism can progress to overt hypothyroidism, so some healthcare providers say it’s useful to take medication. This is especially true if you also have a risk of heart disease, as even mild hypothyroidism can lead to elevated cholesterol levels.
Some evidence suggests, in contrast, that taking medication may have no benefit. A study published in 2014 noted that the widespread prescribing of levothyroxine in people with borderline high levels of TSH may indicate overtreatment.
A healthcare provider can help you weigh the costs and benefits of treatment in your case. They may have you get regular tests to monitor your levels and hold off on taking medication. A healthcare provider may advise taking the medication temporarily if you have symptoms to see if you start to feel better.
You can’t always prevent borderline hyperthyroidism. Some evidence suggests that getting plenty of iodine in your diet can reduce your risk of the condition. Iodine is a mineral the body needs to create thyroid hormones.
Milk and other dairy products, saltwater fish, and iodized table salt are rich sources of iodine. You can also talk to a healthcare provider or pharmacist about iodine supplements. These supplements are generally safe if you take less than 100 micrograms (µg) per day. Taking too much iodine can result in an overactive thyroid.
Borderline hypothyroidism can increase the risk of other conditions, including:
- Cognitive decline: Hypothyroidism might be a risk factor for cognitive decline, such as forgetfulness and memory loss. The thyroid hormone T3 is important for nerve cell function.
- Heart disease: This condition has been linked to hardening of the arteries and heart failure. An underactive thyroid can make it difficult for the heart to pump oxygen-rich blood to the organs.
- Mood changes: People with an underactive thyroid may be at risk for depression. Depression is 1.7 times more common among those with hypothyroidism.
- Pregnancy loss: Hypothyroidism and even subclinical hypothyroidism can impact reproductive function. Both conditions have been linked to an increased risk of miscarriage. Normal TSH levels are important for fetal development. Research has shown that pregnant people who are treated for hypothyroidism are less likely to have a miscarriage.
It’s possible to prevent hypothyroidism if you have an early, mild form of the condition. About 50% of borderline hypothyroidism have normal TSH levels within one to two years. Nearly 25% of those, in contrast, can progress into hypothyroidism.
Keep in mind that the condition can raise the risk of heart disease. It’s important to make lifestyle changes that support heart health if you have borderline hypothyroidism, including:
- Control blood sugar levels if you have diabetes
- Don’t smoke or quit smoking
- Eat a healthy diet that has plenty of nutrients
- Get enough sleep
- Limit alcohol
- Maintain a healthy weight
- Stay physically active
- Take steps to reduce stress, such as meditation, yoga, or tai chi
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