Hypothyroidism: Symptoms, Causes, and Treatment

Hypothyroidism is a condition that affects every 5 in 100 Americans and causes symptoms like weight gain, depression, muscle soreness, and fatigue.

Hypothyroidism: Symptoms, Causes, and Treatment Options - Woman thyroid gland
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Hypothyroidism is a condition in which the thyroid—a butterfly-shaped gland at the base of the neck—doesn't produce enough hormones. The thyroid is part of the endocrine system, which includes other organs and glands that use hormones to regulate metabolism, energy levels, and body temperature.

Hypothyroidism can cause a wide variety of symptoms, ranging from brain fog to lower libido. In contrast, a similar condition called hyperthyroidism occurs when the thyroid produces too many hormones, Rose Lin, MD, an endocrinologist at Providence Saint John's Health Center in Santa Monica, CA, tells Health. Like many thyroid disorders, hypothyroidism is often misdiagnosed or undiagnosed. In fact, a 2019 article published in Advances of Therapy estimated that 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

Although 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, Spencer Kroll, MD, PhD, a board-certified internal medicine specialist with his own private practice in Northern New Jersey, tells Health. Symptoms tend to develop gradually, over the course of many years. According to the National Library of Medicine, these symptoms 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 the above symptoms and they gradually worsen, set up an appointment with your primary care provider or an endocrinologist (a type of doctor who diagnoses and treats endocrine disorders). In addition to hypothyroidism, many of these symptoms are also signs of other conditions, Dr. Lin says.

Hypothyroidism Symptoms in Children and Teens

While hypothyroidism commonly presents in adulthood, one in 4,000 to 5,000 children born in the United States will have the condition, according to Johns Hopkins Medicine. In children, hypothyroidism causes the above symptoms in addition to:

  • Stunted growth
  • Mental development delays
  • Delayed puberty

In infants, hypothyroidism may also cause yellowing of the skin (aka jaundice); a large, swollen tongue; a large soft spot on the head; and a swollen-looking belly where the navel sticks out, per Kids Health.

What Causes Hypothyroidism?

Hypothyroidism occurs when the thyroid doesn't produce enough of the hormones triiodothyronine (T3) and thyroxine (T4). These hormones affect metabolism, body temperature, and heart rate. There are many reasons why the thyroid may be underactive, according to Dr. Lin and Dr. Kroll, including:

  • Hashimoto's thyroiditis, an autoimmune condition that causes chronic inflammation of the thyroid. It is the leading cause of hypothyroidism in the United States
  • Thyroid surgery, where doctors remove part of the thyroid
  • Hyperthyroidism treatments, such as radioactive iodine, that accidentally overcorrect the problem
  • Medications, such as lithium and bexarotene
  • Thyroid nodules, which can be the result of abnormal growth of thyroid cells. While most are noncancerous, they can still disrupt thyroid function.
  • A pituitary gland disorder, which is the area of the brain responsible for regulating the thyroid
  • Iodine deficiency, as iodine is necessary for the production of thyroid hormone

Additionally, there are a few risk factors that heighten the chances of a person developing hypothyroidism, according to the National Library of Medicine. These include:

  • Being a woman
  • Being 60 years old 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 and/or recently undergoing thyroid surgery
  • A history of radiation therapy to the neck, thyroid, or chest

How Is Hypothyroidism Diagnosed?

If a doctor suspects you or your child may have hypothyroidism, they will order a blood test to measure the levels of two hormones: thyroxine (T4) and thyroid-stimulating hormone (TSH). TSH is produced by your pituitary gland and regulates how much T3 and T4 your thyroid releases. If you have an underactive thyroid, the brain releases more TSH to try and boost thyroid hormone levels. High levels of TSH (above 5.9 mlu/L) and low levels of T4 (below 5.0 μg/d) indicate an underactive thyroid, which in turn results in a hypothyroidism diagnosis, per UCLA Health. The normal range for TSH and T4 for children will vary depending on their age, but diagnosis is also based on high levels of TSH and low levels of T4.

If your TSH levels are high but your T4 reading is relatively normal (i.e. between 0.5 and 5.0 mIU/L), it means you may have subclinical hypothyroidism, an early form of the condition that affects up to 20% of adults, according to a 2019 review published in the Cleveland Clinic Journal of Medicine. Although subclinical hypothyroidism is asymptomatic in 70% of cases, it does increase a person's chances of developing hypothyroidism later in life.

Hypothyroidism Treatment

While hypothyroidism can not be "cured," medicine can manage the condition. For most patients, the standard treatment for hypothyroidism is taking prescription thyroid hormone—either in a tablet or liquid form—for the rest of their life, according to Dr. Lin. Most people start feeling better within six to eight weeks of starting medication since the synthetic hormones will lower TSH levels back to their normal range. Treatment is the same for children, although some children may outgrow the disorder, per Cedars Sinai.

Once you begin treatment, your doctor will likely order another blood test to check your TSH levels and make any necessary adjustments to your medication dose. Which dose you take will depend on how functional your thyroid is, according to the National Library of Medicine.

While consistently taking your thyroid medication is crucial for managing the condition, you can also make small dietary changes to further alleviate symptoms. For example, you may want to try eating more iodine-rich foods—like fish and dairy—if you have low blood levels of the mineral, according to Dr. Kroll. The thyroid needs iodine to produce hormones. You'll also want to limit or avoid foods known as goitrogens—like soy and kale—which cause an underactive thyroid to swell, further exacerbating symptoms.

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