What Is Hypothyroidism?

Hypothyroidism occurs when the thyroid doesn't produce enough hormones. In contrast, hyperthyroidism occurs when the thyroid produces too many hormones.

The thyroid, part of the endocrine system, is the butterfly-shaped gland at the base of the neck. The endocrine system uses hormones to regulate metabolism, energy levels, and body temperature.

Hypothyroidism can cause many symptoms, ranging from brain fog to low libido. Like many thyroid disorders, hypothyroidism is often misdiagnosed or undiagnosed. In fact, about 5% of people with hypothyroidism are undiagnosed.

Here's what you need to know about hypothyroidism, including common symptoms, causes, and potential treatment options.

Hypothyroidism Symptoms

Hypothyroidism affects almost five in every 100 people in the United States. Symptoms vary widely based on sex, age, menstrual status, weight, and fat distribution. Typically, symptoms develop gradually over many years and include:

• Fatigue
• Constipation
• Dry, thinning hair
• Inability to tolerate cold temperatures
• Tingling and numbness in hands and feet
• Weight gain
• Slow heart rate
• Depression
• Face and eye puffiness
• Brain fog
• Heavy and irregular menstrual periods
• Muscle soreness

If you're experiencing any of those symptoms gradually worsening, consult a healthcare provider. An endocrinologist is a healthcare provider who diagnoses and treats endocrine system disorders. 

Hypothyroidism Symptoms in Children and Infants

Hypothyroidism usually occurs in adulthood. Still, children can also have the condition. Specifically, children may have the following symptoms:

• Stunted growth
• Mental development delays
• Delayed puberty

Additionally, in infants, hypothyroidism cause symptoms like:

• Jaundice, or the yellowing of the skin
• Hearing loss
• Swollen tongue
• Difficulty breathing
• Poor feeding
• Umbilical hernia

What Causes Hypothyroidism?

Hypothyroidism occurs when the thyroid doesn't produce enough of the hormones triiodothyronine (T3) and thyroxine (T4). Those hormones affect metabolism, body temperature, and heart rate. 

There are many reasons why the thyroid may be underactive, including:

• Hashimoto's thyroiditis: This autoimmune condition causes chronic inflammation of the thyroid. Hashimoto's thyroiditis is the leading cause of hypothyroidism in the United States.
• Thyroid surgery: A healthcare provider removes part of the thyroid with this type of surgery.
• Hyperthyroidism treatments: Some treatments for an overactive thyroid, like radioactive iodine, may overcorrect the issue.
• Medications: Lithium and bexarotene may contribute to an underactive thyroid.
• Thyroid nodules: These are abnormal growth of thyroid cells. While most thyroid nodules are noncancerous, they can disrupt thyroid function.
• A pituitary gland disorder: This occurs when something impacts the area of the brain responsible for regulating the thyroid.
• Iodine deficiency: Iodine helps produce thyroid hormones. So, a deficiency in the mineral may contribute to an underactive thyroid.

Risk Factors

Some people are more likely to develop hypothyroidism. The risk factors include:

• Being a woman
• Being 60 years or older
• Having a family history of thyroid disease
• Having an autoimmune disease
• Being pregnant or giving birth in the last six months
• Having a history of thyroid problems or recently undergoing thyroid surgery
• Having a history of radiation therapy to the neck, thyroid, or chest

How Is Hypothyroidism Diagnosed?

To diagnose hypothyroidism, a healthcare provider will likely do the following:

• Ask about your medical history, including symptoms you have
• Perform a physical exam
• Order a blood test to measure thyroid-stimulating hormone (TSH), T4, T3, and thyroid antibodies
• Order imaging tests, such as a thyroid scan, ultrasound, or radioactive iodine uptake test

Your pituitary gland produces TSH, which regulates how much T3 and T4 your thyroid releases. If you have an underactive thyroid, your pituitary gland releases more TSH to boost thyroid hormone levels.

High levels of TSH and low levels of T4 indicate an underactive thyroid, indicating hypothyroidism. The normal range for TSH and T4 for children varies depending on age. But high levels of TSH and low levels of T4 also inform diagnosis.

If your TSH levels are high, but your T4 reading is relatively normal, you may have subclinical hypothyroidism. Subclinical hypothyroidism is an early form of the condition. In about 70% of cases, subclinical hypothyroidism is asymptomatic. Still, the condition increases the risk of later developing hypothyroidism.

Treatments for Hypothyroidism

There's no cure for hypothyroidism. However, medicine can manage symptoms. In most cases, prescription thyroid hormone, either in a tablet or liquid form, is the standard treatment. Most people feel better within six to eight weeks of starting medication. The synthetic hormones will lower TSH levels back to their normal range.

Once you begin treatment, a healthcare provider will order another blood test in six to eight weeks to check your TSH levels. The healthcare provider will adjust your medication dose as necessary, depending on the results. The dose will continue to change until thyroid hormone levels are in the normal range.

Consistently taking the medication is key to managing the condition. Still, you can also make small dietary changes to alleviate symptoms further. 

For example, the thyroid gland needs iodine to produce hormones. So, if you have low blood levels of the mineral, you may want to try eating more iodine-rich foods like:

• Fish, particularly cod
• Seaweed
• Dairy

You'll also want to limit or avoid goitrogens, like soy and kale. Goitrogens cause an underactive thyroid to swell, which worsens symptoms.

A Quick Review

Hypothyroidism occurs when the thyroid doesn't make enough of the hormones that regulate metabolism, temperature, and heart rate. The symptoms can vary widely and usually develop gradually over several years. The condition is common among adults, but children may have symptoms. 

If you're experiencing symptoms, talk with a healthcare provider. In particular, an endocrinologist can run tests to determine if you have an underactive thyroid.