November 2025

Weight gain, cold hands, and ongoing fatigue can indicate many different health conditions. One that often comes up is hypothyroidism. Perhaps you’ve heard of this thyroid disease but aren’t sure what it is or why it1s important.

Get answers to common questions about hypothyroidism and learn how to manage your thyroid health.

What is your thyroid, and why does it matter?

Your thyroid is a butterfly-shaped gland found in the front part of your neck. It makes hormones that play a major role in metabolism, growth, and development.

What is hypothyroidism?

Hypothyroidism is the most common thyroid disease. It’s when the thyroid gland doesn’t make and release enough thyroid hormone into your bloodstream.

Roughly 5% of people aged 12 and older have hypothyroidism, according to the National Institute of Diabetes and Digestive and Kidney Diseases. Anyone can develop hypothyroidism, but it affects women much more than men.

Symptoms include:

• Brittle nails.
• Dry skin.
• Dry, thinning hair.
• Heavy or irregular periods.
• Fatigue.
• Feeling cold often or having problems tolerating cold.
• Fertility problems.
• Mood changes, especially depression.
• Slowed heart rate
• Weight gain or difficulty losing weight.

What is hyperthyroidism?

Far less common than hypothyroidism is hyperthyroidism, which is when your thyroid makes too much thyroid hormone. This problem
affects roughly 1% of people ages 12 and older.

You are more likely to have hyperthyroidism if you:

• Are female.
• Are age 60 or older.
• Have a family history of thyroid disease
• Eat a lot of food that contains iodine.
• Have pernicious anemia, diabetes, or primary adrenal insufficiency.
• Take medication that contains iodine.
• Smoke or use other products that contain nicotine.

How is hypothyroidism diagnosed?

Doctors diagnose hypothyroid problems using thyroid blood tests. These measure your thyroid hormone levels. Your doctor may also use ultrasound imaging to view your thyroid health.

Blood and imaging tests help your doctor determine whether you have thyroid disease and what type it is.

What are the treatments for hypothyroid disease?

Hypothyroidism doesn’t go away on its own. Dietary supplements and over-the-counter medicines can’t fix it.

Left untreated, hypothyroidism can lead to high cholesterol. In pregnant women, it can cause problems for women and their babies. In severe cases, it can lead to a life-threatening coma.

To get what your body needs to function properly, you need to take a prescription thyroid replacement hormone. The generic name is levothyroxine. You can get it in pill, soft gel capsule, or liquid form.

After treatment begins, you will need follow-up blood tests to see how it is working. Your doctor may adjust the medication dose and conduct additional blood tests until your thyroid hormone levels are within the normal range.

Can you prevent hypothyroidism?

Most of the time, the most common causes of hypothyroidism are not preventable.

Your thyroid gland needs a trace mineral called iodine to make thyroid hormone. We get iodine through food, mainly iodized table salt and foods made with iodized salt. When you don’t get the amount of iodine your body needs — called iodine deficiency — you can develop goiter and hypothyroidism.

Iodine deficiency is rare in the U.S. thanks to the addition of iodine to table salt over a century ago. According to the Mayo Clinic, using iodized salt is one of the easiest ways to get your body’s iodine needs. Only salt labeled “iodized” contains iodine. According to the National Institutes of Health Office of Dietary Supplements, most people in the U.S. meet or exceed the recommended dietary allowance of daily iodine.

Common causes of hypothyroidism

Hashimoto’s thyroiditis is the most common cause of hypothyroidism. It’s an autoimmune disorder in which the body’s immune system attacks the thyroid gland, causing inflammation. When this happens, the thyroid can’t make enough thyroid hormones.

Other common causes of hypothyroidism include:

• Thyroiditis, inflammation of the thyroid gland.
• Congenital hypothyroidism — you are born with it.
• Radiation treatment for hyperthyroidism or head and neck cancers.
• Surgical removal of part or all of the thyroid. You may need this if you have hyperthyroidism, thyroid cancer, tumors that cause excess thyroid hormone, or goiter, an enlargement of the thyroid gland.

How does diet impact hypothyroidism?

If you have Hashimoto’s or another autoimmune thyroid disorder, too much iodine in your diet can actually worsen hypothyroid symptoms. So, you need to watch what you eat.

High-iodine foods

Avoid or limit these high-iodine foods and products:

• Seaweed, such as kelp, nori, kombu, and wakame. Sushi rolls often contain a layer of seaweed.
• Fish and seafood. Codfish and oysters are especially high in iodine.
• Eggs.
• Processed foods that contain iodine.
• Supplements that contain iodine.
• Certain cough syrups, as some may contain iodine.

Ask your doctor whether you need to switch from iodized salt to plain salt. Other preventive measures, such as managing stress, exercising regularly to regulate hormone levels, getting sufficient sleep, and prioritizing regular checkups, can help maintain a healthy thyroid.