What Hypothyroidism Can Do to Your Body

Medically Reviewed by Neha Pathak, MD on December 01, 2017
4 min read

You probably don’t think much about your thyroid. Fact is, that tiny gland in your neck has a huge job. It makes hormones that control your metabolism, the process that turns food into energy. It also has a hand in just about every other function in your body. Brain, muscles, digestion -- your thyroid makes them all run smoothly.

When you don’t have enough thyroid hormone, a condition called hypothyroidism or low thyroid, your system slows down. Over time, you might forget things, feel cold, tired, or depressed, or you may put on a few pounds -- though most weight gain isn’t due to a sluggish thyroid.

Most of these symptoms get better or go away when you replace the hormone your thyroid no longer makes. Man-made thyroid hormone works just like your own and can help get your body back on track. But if low levels aren't treated -- or you stop taking the medicine -- other conditions may pop up. 

This is swelling in your neck that happens if your thyroid gland is bigger than normal. When you don’t have enough thyroid hormone, your pituitary gland tells your thyroid to make more. It tries to keep up by growing larger.

A goiter usually doesn’t hurt. But it can cause a cough or trouble swallowing. Taking thyroid hormone can stop a goiter from growing. But it may not get rid of it completely.

When your metabolism slows, many things can happen. You’ll probably feel tired and sluggish, be constipated, and you may gain weight, explains Adrian Dobs, MD, an endocrinologist at Johns Hopkins.

“Some people feel very sick, but that’s not common,” she says.

As for those extra pounds, they can be tough to shed, according to Marilyn Tan, MD, chief of the Stanford Endocrine Clinic. Treatment alone won’t reverse the weight gain, she says. “You really have to work at it.”

Your thyroid helps control how fast new skin cells replace old ones. When this process slows, your skin can feel rough and dry. You may notice some hair loss, too, Dobs says. You won’t go bald, but your hair might not look as thick and full as it did before.

Women with untreated hypothyroidism can have menstrual periods that happen less often, or last longer than normal. Bleeding may be heavier than usual, too.

Both men and women could become less fertile or lose some of their sex drive.

Dobs says women who have trouble getting pregnant should always have a thyroid test.

If you’re pregnant and have hypothyroidism that’s not treated, your baby could be born too early or have a slightly lower IQ than normal. Even when you already take thyroid medicine, be sure to tell you doctor if you’re pregnant. You may need a higher dose of thyroid hormone. You might need to get tested more often, too.

Too little thyroid hormone can make it hard for you to think clearly or remember things. You could feel a little fuzzy or jet-lagged, even when you haven’t left home. Your mood might change, too. You may feel more down than normal. If you were depressed, you may feel worse.

This doesn’t happen overnight. It can take years for your symptoms to show up.

Severe, untreated hypothyroidism can cause fluid buildup that puts pressure on the nerves in your arms and legs. This can lead to tingling, pain, and numbness where the nerve is damaged. Low thyroid can sometimes lead to carpal tunnel syndrome, which affects the nerves in your hand and wrist.

Hypothyroidism can slow your heart rate, drop your blood pressure, and put fluid around your heart. It can also lead to high levels of LDL or “bad” cholesterol, but that may have to wait, Dobs says.

“Before treating [people] with high doses of statins (medicines that lower cholesterol), it’s important to get any underlying thyroid problem under control,” she explains.

Low thyroid can sometimes lead to heart failure. This doesn’t mean your heart stops beating. It’s that your heart can’t pump enough blood to meet your body’s needs.

Severe low thyroid can weaken the muscles that help you breathe. Some experts think this is why hypothyroidism can lead to pauses in your breathing while you sleep, a condition called sleep apnea. These pauses can last a few seconds to a few minutes and can happen up to 30 times an hour.

Most of these problems only happen when you have severe low thyroid, and some are rare, Dobs says. Many people have few if any symptoms, even if they’ve had hypothyroidism for years.

Still, if you have low thyroid, it’s important to get it treated. Your system may be slowing down, even if you don’t feel it.