What Happens if Hypothyroidism Is Left Untreated?

Complications of untreated underactive thyroid range from infertility to a life-threatening slowdown of basic bodily functions.

Fatigue is among the many risks when hypothyroidism is not treated.iStock

The thyroid gland is a small, butterfly-shaped organ in your neck that produces thyroid hormones, which are essential for many of your body’s functions, including how your body uses energy.

If your thyroid gland does not make enough thyroid hormone — a condition known as hypothyroidism or underactive thyroid — your body will not function optimally and your metabolism may slow down.

This can happen for a number of reasons, but the?most common cause of hypothyroidism?in the United States is Hashimoto’s thyroiditis, an autoimmune disorder in which your body’s immune system attacks the thyroid, causing serious damage to the thyroid tissue.

Symptoms can vary from person to person, but?common symptoms of hypothyroidism?include:

  • Fatigue
  • Weight gain
  • Constipation
  • Dry skin
  • Dry or thinning hair

Treatment for hypothyroidism?is fairly straightforward and involves taking replacement thyroid hormone. While it may take some trial and error to find the right dose of medication, proper treatment usually reverses the symptoms of hypothyroidism.

However, there are a number of reasons people may not properly treat their hypothyroidism. They may stop taking medication because they’re experiencing side effects or because they’re not noticing benefits of the medication, for example. Or they may not know they have hypothyroidism. In this case, the condition can gradually become more severe and potentially cause a range of complications.

Because your thyroid affects so many areas of your body, untreated hypothyroidism can cause widespread harm. Here are seven complications to watch out for.

1. Goiter

A goiter is an?enlarged thyroid?gland, and it happens when the organ is trying extra hard to make thyroid hormone.

“Your endocrine system works in feedback loops,” notes?Tracy S. Tylee, MD, an endocrinologist at the University of Washington Medical Center in Seattle. Specifically, your pituitary gland (located at the base of your brain) tells your thyroid how much thyroid hormone to make, and it monitors your thyroid hormone levels to determine this.

To stimulate your thyroid, your pituitary gland creates a hormone called?thyroid-stimulating hormone?(TSH). If your thyroid hormone level is low, your pituitary will make more TSH in an attempt to make your thyroid work harder.

A goiter happens when the pituitary “is hammering the thyroid, trying to get more thyroid hormone out of it,” says Dr. Tylee. “When that happens, the thyroid gets bigger and bigger as it’s trying to make more thyroid hormone.”

Goiters are relatively common, and most are painless and not indicative of a more serious thyroid problem, according to the Cleveland Clinic. But they can be an early warning sign of thyroid dysfunction — even before your thyroid hormone levels fall below normal. In most cases of goiters, your doctor will likely check your TSH levels as a precaution, notes the Cleveland Clinic.

In addition, a large goiter may interfere with your swallowing or breathing, or cause you to be self-conscious about your appearance.

2. Heart Disease

There are at least two ways that?hypothyroidism can contribute to heart disease, according to Tylee. It tends to make your body retain fluid, which can lead to?hypertension?(high blood pressure) and?congestive heart failure?(a condition in which your heart can’t pump blood adequately).

Fluid retention?is one reason?people with hypothyroidism?often gain weight, and the extra weight looks different than weight gain based on fat tissue. “You tend to get puffy ankles and a puffy face” with fluid retention, says Tylee.

Another way that hypothyroidism can increase your heart risk is by raising your lipid (cholesterol and triglyceride) levels. These substances can contribute to a fatty buildup on the lining of arteries, known as?atherosclerosis.

Tylee emphasizes that it’s a good idea to check for thyroid problems in people with elevated lipids. “If you treat their thyroid disease, a lot of times the lipids will get better on their own,” she notes.

Hypothyroidism may also have a separate effect on your risk of?coronary artery disease?(which involves atherosclerosis in the arteries leading to your heart) by contributing to dysfunction in the lining of blood vessels, according to a study.

3. Kidney Disease

One area of emerging research is the effect of hypothyroidism on kidney function. In a study in the journal Scientific Reports,?researchers looked at data from wide-ranging voluntary health examinations performed on Taiwanese adults.

Using a measure called estimated glomerular filtration rate (eGFR) as well as looking at levels of protein in participants’ urine, the researchers found that people with hypothyroidism had a 2.41 higher risk of chronic kidney disease than people with normal thyroid function.

The study included people with subclinical hypothyroidism?(in which TSH is elevated but thyroid hormone levels are normal), who were 2.04 times as likely to have kidney disease; and those with overt hypothyroidism (in which thyroid hormone levels are low), who were 7.61 times as likely to have kidney disease.

Other research has also shown decreased eGFR in people with severe hypothyroidism, which is reversed by taking thyroid hormone.

4. Peripheral Neuropathy

Uncontrolled hypothyroidism can damage your peripheral nerves, which carry information from your brain and spinal cord to the rest of your body. One reason for this may be fluid retention, which puts excess pressure on the nerves.

Symptoms of?peripheral neuropathy?often include pain, numbness, or tingling in your arms or legs, and may also include muscle weakness or partial loss of muscle control.

However, in most cases, peripheral neuropathy is caused by something other than hypothyroidism.

In a study of previously unexplained neuropathy,?researchers found that only 0.7 percent of cases were due to hypothyroidism, compared with 25.3 percent of cases caused by diabetes or?prediabetes.

5. Cognitive Issues

Mental and emotional difficulties are common in hypothyroidism. “The thing that people most describe is just difficulty focusing,” says Tylee. “They feel like they’re in a cloud.”

Hypothyroidism can also contribute to depression. In these cases, treatment with thyroid hormone?can help reverse symptoms of depression.

One study evaluated people with both subclinical hypothyroidism and depression who were then randomly assigned to take either thyroid hormone or a placebo (inactive pill). After 12 weeks, depression scores improved significantly in the thyroid hormone group, but not in the placebo group.

Even if you’re not aware that hypothyroidism is affecting your mental or emotional status, this effect may become clear once you begin treatment. “They feel so much better that it becomes apparent in retrospect,” says Tylee about many of her own patients.

6. Fertility Issues

In many women with hypothyroidism, menstrual periods become irregular and unpredictable. This can have a negative impact on?fertility.

In a study,?69 infertile women with subclinical hypothyroidism were given thyroid?hormone treatment. After this, 84.1 percent successfully conceived within an average time of less than a year, although 29.3 percent later miscarried.

7. Myxedema (Coma)

Myxedema is a rare but life-threatening complication of severe hypothyroidism that involves extreme fatigue and impaired cognition, followed by loss of consciousness.

In someone with untreated hypothyroidism, a myxedema coma can be triggered by stress on the body, an infection, or taking?sedatives, according to the?Mayo Clinic.

Tylee stresses that myxedema is a medical emergency, and although it’s rare, some people are at increased risk — such as elderly people and those who live alone. Often, she says, “they get sick with something else, like a heart attack or?pneumonia,” and that can lead to myxedema.

Both myxedema and certain other cases of severe hypothyroidism require intravenous (IV) delivery of thyroid hormone, since fluid in the gut lining may prevent absorption of oral drugs.

But Tylee emphasizes that doctors should check for hypothyroidism well before severe symptoms develop.

“It’s important that if someone comes in complaining of feeling tired and having trouble focusing, you don’t just attribute that to stress and depression,” she says. “You should check their?thyroid levels, because that’s something you can fix.”

Editorial Sources and Fact-Checking

Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.

Resources

  • Goiter.?Cleveland Clinic. June 5, 2022.
  • Sara JD et al. Hypothyroidism Is Associated With Coronary Endothelial Dysfunction in Women.?Journal of the American Heart Association. August 25, 2015.
  • Chang YC et al. Subclinical and Overt Hypothyroidism Is Associated With Reduced Glomerular Filtration Rate and Proteinuria: A Large Cross-Sectional Population Study.?Scientific Reports. February 1, 2018.
  • Rhee CM. The Interaction Between Thyroid and Kidney Disease: An Overview of the Evidence.?Current Opinion in Endocrinology, Diabetes and Obesity. October 2016.
  • Farhad K et al. Causes of Neuropathy in Patients Referred as “Idiopathic Neuropathy.” Muscle & Nerve. June 2016.
  • Najafi L et al. Depressive Symptoms in Patients With Subclinical Hypothyroidism — the Effect of Treatment With Levothyroxine: A Double-Blind Randomized Clinical Trial.?Endocrine Research. March 16, 2015.
  • Yoshioka W et al. Thyroxine Treatment May Be Useful for Subclinical Hypothyroidism in Patients With Female Infertility.?Endocrine Journal. 2015.
  • Hypothyroidism (Underactive Thyroid): Symptoms and Causes.?Mayo Clinic. December 10, 2022.
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