Subclinical Hypothyroidism: Symptoms, Causes, Diagnosis, and Treatment

Subclinical hypothyroidism is an endocrine disorder caused by abnormal secretion of thyroid hormones. Though it can be cured by taking thyroid hormone replacement medicines, there are situations where doctors suggest waiting for an automatic cure. 

This article provides detailed insights into its symptoms, causes, complications, treatment methods, and more.

Causes of Subclinical Hypothyroidism

Multiple glands and hormones in the endocrine system control the TSH (thyroid-stimulating hormone) level in one’s bloodstream. First, the hypothalamus secretes thyroid-releasing hormone (TRH), causing the pituitary gland to release TSH.

Then, TSH stimulates the thyroid cells to produce 80% T4 (thyroxine) and 20% T3 (triiodothyronine) in the bloodstream. Once both these hormones reach their maximum level, they signal the pituitary gland to stop TSH production and complete the cycle until their level drops.

In subclinical hypothyroidism, this hormone production cycle is affected due to thyroid inflammation or disorders. Thus, the level of the T4 hormone stays normal despite TSH elevation, which causes this condition.

Risk Factors of Subclinical Hypothyroidism

Most of the factors that increase the chances of subclinical hypothyroidism are difficult to control. Some of them are as follows:

• Age: Thyroid-stimulating hormone increases with age, which can develop subclinical hypothyroidism in older age groups.
• Gender: Though not clearly stated, estrogen (female hormone) plays a crucial role in developing subclinical hypothyroidism, according to the Journal of Endocrinology and Metabolism. Thus, there is a higher risk of subclinical hypothyroidism in women than in men. 
• Iodine Intake: Adequate thyroid functioning requires iodine but in a limited amount. Excessive iodine intake can increase the risks of subclinical hypothyroidism.

Symptoms of Subclinical Hypothyroidism

In most cases, subclinical hypothyroidism is asymptomatic (has no symptoms). However, in some cases, mild symptoms can be noticed. Following are the symptoms that one should look for:

• Intolerance to cold temperatures
• Skin and hair dryness
• Constipation
• Fatigue
• Unusual weight gain
• High blood pressure
• Low attention or depression
• Heavy menstrual flow, etc.

Subclinical Hypothyroidism Diagnosis

Thyroid function blood tests are the most prevalent way to diagnose subclinical hypothyroidism. It helps assess the right amount of thyroid-stimulating hormone (TSH) in one’s body, thereby detecting subclinical hypothyroidism. 

The normal TSH level for an adult is 0.4 to 4.5 mIU/L. However, it may differ for a pregnant woman by trimester. If an individual’s blood test report shows normal T4 levels and higher TSH levels between 5 and 10 mIU/L, the person may have subclinical hypothyroidism.  

Based on the TSH levels, subclinical hypothyroidism has two categories:

• Grade 1: TSH level is 4.5 – 9.9 mIU/L 
• Grade 2: TSH level is 10 mIU/L or more

Several non-thyroid factors may increase the TSH level. To avoid misdiagnosing subclinical hypothyroidism with such issues, one must know the non-thyroid factors that lead to TSH elevation. Those factors include:

• Nonthyroidal illness
• Addison’s Disease (insufficient adrenal production)
• Renal failure
• Medications like lithium, metoclopramide, ritonavir, amiodarone, tyrosine kinase inhibitors, etc.
• Ageing due to TSH level rise

Complications Associated with Subclinical Hypothyroidism

Patients with subclinical hypothyroidism may witness the following complications:

• Cardiovascular Complications: Whether subclinical hypothyroidism relates to cardiovascular issues or not is still a debate. As per studies, older people with 7 mIU/L or more TSH levels are twice the risk of congestive heart failure than those with normal levels. If left untreated, subclinical hypothyroidism can lead to high cholesterol and blood pressure.
• Functional Capacity: Subclinical hypothyroidism decreases a person’s muscular and exercise strength. Studies have shown that after getting treatment for 6 months, such patients have experienced increased physical workouts.
• Cognitive Impairment: Some studies show that subclinical hypothyroidism patients aged 75 years or above have higher risks of cognitive decline. However, some patients show no such risk, indicating that this complication can vary from person to person.
• Depression: Subclinical hypothyroidism patients aged 60 years or below have been diagnosed with depression syndromes. However, patients above 60 are not associated with such issues. Even after treatment with levothyroxine replacement, no changes in depression have been noticed.

Management and Treatment of Subclinical Hypothyroidism

There are different opinions regarding the necessity of subclinical hypothyroidism treatment. Though treatment reduces the risks of CVD (cardiovascular disease), it can cause thyrotoxicosis (excessive thyroid hormones in the human body). Individuals 65 years of age or older have a higher risk of thyrotoxicosis.

In most cases, subclinical hypothyroidism has no symptoms, leaving no scope for starting the treatment process. Even after diagnosis, doctors mostly suggest patients wait for subclinical hypothyroidism to cure on its own. However, for the following patients, treatment is necessary:

• Middle-aged or youth with mild hypothyroidism symptoms
• Individuals having 10 mIU/L or higher TSH level 
• Middle-aged or youth with cardiovascular risks

The treatment process for subclinical hypothyroidism includes thyroid hormone replacement therapy. Doctors prescribe levothyroxine pills in such conditions. However, doctors suggest a blood test to check the TSH level before starting medication.

While on medication, one should opt for blood tests at regular intervals to check their thyroid health from time to time. High dosages of levothyroxine may also cause hyperthyroidism, so regular blood tests and consultation with the doctor are necessary. 

Lifestyle and Dietary Management of Subclinical Hypothyroidism

As per research, changes in diet and adopting regular physical activities can influence conditions like body fats, elevated LDL, insulin resistance, etc., in subclinical hypothyroidism patients. Intaking selenium and phytoestrogens through soy protein can regulate the TSH level. 

Daily exercise like swimming and weight training can also maintain a healthy hormonal balance, but research has not yet confirmed this. 

Conclusion

If treated on time, subclinical hypothyroidism can prevent heart issues and other disorders. However, to treat it at the right time, one must understand its symptoms, causes, and risk factors. Besides, regular monitoring of thyroid function is necessary for physicians to change the medication dosage.