Thyroid disorders are common. In fact, about 12% of people will experience abnormal thyroid function at some point during their lives.
Women are eight times more likely to develop a thyroid disorder than men. Also, thyroid problems increase with age and may affect adults differently than children.
At the most basic level, thyroid hormone is responsible for coordinating energy, growth and metabolism in your body.
Problems can occur when this hormone's levels are too high or low.
Hypothyroidism, or low levels of thyroid hormone, slows your metabolism and decreases growth or repair of many parts of the body.
What Is Hypothyroidism?
The thyroid is a small, butterfly-shaped gland that drapes across the front of your windpipe.
If you place your fingers on the sides of your Adam's apple and swallow, you'll feel your thyroid gland sliding under your fingers.
It releases thyroid hormone, which controls the growth and metabolism of essentially every part of your body.
The pituitary, a tiny gland in the middle of your head, monitors your physiology and releases thyroid-stimulating hormone (TSH). TSH is the signal to the thyroid gland to release thyroid hormone (1).
Sometimes TSH levels increase, but the thyroid gland can't release more thyroid hormone in response. This is known as primary hypothyroidism, as the problem begins at the level of the thyroid gland.
Other times, TSH levels decrease, and the thyroid never receives the signal to increase thyroid hormone levels. This is called secondary hypothyroidism.
Hypothyroidism, or "low thyroid," can cause a variety of signs and symptoms. This article will help you recognize and understand these effects.
Here are 10 common signs and symptoms of hypothyroidism.
1. Feeling Tired
One of the most common symptoms of hypothyroidism is feeling worn out. Thyroid hormone controls energy balance and can influence whether you feel ready to go or ready to nap.
As an extreme example, animals that hibernate experience low thyroid levels leading up to their long sleep (2).
Thyroid hormone receives signals from the brain and coordinates cells to change their functions, depending on what else is going on in your body.
Those with high levels of thyroid hormone feel nervous and jittery. In contrast, people with low thyroid feel exhausted and sluggish.
Low-thyroid individuals feel unrested, even though they may be sleeping more.
Feeling sleepier than usual without a good explanation could be a sign of hypothyroidism.
Summary: Thyroid hormone is like a gas pedal for energy and metabolism. Low thyroid hormone levels leave you feeling drained.
2. Gaining Weight
Unexpected weight gain is another common symptom of hypothyroidism (7).
Not only are low-thyroid individuals moving less — they're also signaling their livers, muscles and fat tissue to hold on to calories.
When thyroid levels are low, metabolism switches modes. Instead of burning calories for growth and activity, the amount of energy you use at rest, or your basal metabolic rate, decreases. As a result, your body tends to store more calories from the diet as fat.
Because of this, low thyroid hormone levels can cause weight gain, even if the number of calories eaten remains constant.
If you've been experiencing weight gain, first consider whether other changes in your lifestyle might explain it.
If you seem to be gaining weight in spite of a good diet and exercise plan, bring it up with your doctor. It might be a clue that something else is going on.
Summary: Hypothyroidism signals the body to eat more, store calories and burn fewer calories. This combination leads to weight gain.
3. Feeling Cold
Heat is a byproduct of burning calories.
For example, consider how hot you get when you workout. This is because you are burning calories.
Even when you're sitting, you're burning a small amount of calories. However, in cases of hypothyroidism, your basal metabolic rate decreases, reducing the amount of heat you generate.
In addition, thyroid hormone turns up the thermostat on brown fat, which is a specialized type of fat that generates heat. Brown fat is important in maintaining body heat in cold climates, but hypothyroidism prevents it from doing its job (9).
That's why low levels of thyroid hormone cause you to feel colder than others around you. About 40% of low-thyroid individuals feel more sensitive to cold than usual (6).
If you've always wanted the room warmer than the people you live and work with, this may just be the way you are built.
But if you've noticed yourself feeling colder than normal lately, it could be a sign of hypothyroidism.
Summary: Low thyroid hormone slows down your body's normal heat production, leaving you cold.
4. Weakness and Aches in Muscles and Joints
Low thyroid hormone flips the metabolic switch toward catabolism, which is when the body breaks down body tissues like muscle for energy (10).
During catabolism, muscle strength decreases, potentially leading to feelings of weakness. The process of breaking down muscle tissue can also lead to aching (11).
Everyone feels weak once in a while. However, people with hypothyroidism are twice as likely to feel more weak than usual, compared to healthy people (6).
Additionally, 34% of low-thyroid individuals get muscle cramps in the absence of recent activity (6).
One study in 35 individuals with hypothyroidism showed that replacing low levels of thyroid hormone with a synthetic thyroid hormone called levothyroxine improved muscle strength and decreased aches and pains, compared to no treatment (12).
Another study showed a 25% improvement in the sense of physical well-being among patients receiving thyroid replacement (13).
Weakness and aches are normal following strenuous activity. However, new, and especially increasing, weakness or aching is a good reason to make an appointment with your physician.
Summary: Low levels of thyroid hormone slow down your metabolism and can cause painful muscle breakdown.
5. Hair Loss
Like most cells, hair follicles are regulated by thyroid hormone.
Because hair follicles have stem cells that have a short lifespan and rapid turnover, they are more sensitive to low thyroid levels than other tissues (14).
Low thyroid hormone causes hair follicles to stop regenerating, resulting in hair loss. This will typically improve when the thyroid issue is treated.
In one study, about 25–30% of patients seeing a specialist for hair loss were found to have low thyroid hormone. This increased to 40% in individuals over 40 (15).
Furthermore, another study showed that hypothyroidism may cause coarsening of the hair in up to 10% of individuals with low thyroid hormone (6).
Consider hypothyroidism if you experience unexpected changes in the rate or pattern of your hair loss, particularly if your hair becomes patchy or coarser.
Other hormone problems can also cause unexpected hair loss. Your doctor can help you sort out whether your hair loss is anything to worry about.
Summary: Low thyroid hormone affects rapidly growing cells like hair follicles. This can cause hair loss and coarsening of the hair.
6. Itchy and Dry Skin
Like hair follicles, skin cells are characterized by rapid turnover. Therefore, they are also sensitive to losing growth signals from the thyroid hormone.
When the normal cycle of skin renewal is broken, skin may take longer to regrow.
This means the outer layer of skin has been around longer, accumulating damage. It also means that dead skin may take longer to shed, leading to flaky, dry skin.
One study showed 74% of low-thyroid individuals reported dry skin. However, 50% of patients with normal thyroid levels also reported dry skin from other causes, making it hard to know if thyroid problems were the cause (6, 16).
Additionally, the study showed that 50% of people with hypothyroidism reported that their skin had gotten worse over the past year.
Changes in skin that cannot be blamed on allergies like hay fever or new products can be a more practical sign of thyroid problems.
Finally, hypothyroidism is sometimes caused by autoimmune disease. This can affect the skin, causing swelling and redness known as myxedema. Myxedema is more specific to thyroid problems than other causes of dry skin (16).
Summary: Hypothyroidism commonly causes dry skin. However, most people with dry skin do not have hypothyroidism. Myxedema is a red, swollen rash that is characteristic of thyroid problems.
7. Feeling Down or Depressed
Hypothyroidism is linked to depression. The reasons for this are unclear, but it might be a mental symptom of an overall decrease in energy and health (17).
64% of women and 57% of men with hypothyroidism report feelings of depression. About the same percentage of men and women also experience anxiety (18).
In one study, thyroid hormone replacement improved depression in patients with mild hypothyroidism, compared to a placebo (19).
Another study of young women with mild hypothyroidism showed increased feelings of depression, which were also connected to decreased satisfaction with their sex lives (18).
Feeling depressed is a good reason to talk to a physician or therapist. They may be able to help you cope, regardless of whether the depression is caused by thyroid problems or something else.
Summary: Hypothyroidism can cause depression and anxiety. These conditions are shown to improve with thyroid hormone replacement.
8. Trouble Concentrating or Remembering
Many patients with hypothyroidism complain of mental "fogginess" and trouble concentrating. The way this mental fogginess presents itself varies by person.
In one study, 22% of low-thyroid individuals described increased difficulty doing everyday math, 36% described thinking more slowly than usual and 39% reported having a poorer memory (6).
In another study of 14 men and women with untreated hypothyroidism, the participants showed difficulty remembering verbal cues (4).
Difficulties in memory or concentration can happen to everyone, but if they are sudden or severe, they could be a signal of hypothyroidism.
Summary: Hypothyroidism can cause mental fogginess and difficulty concentrating. It may also impair certain kinds of memory.
Low thyroid levels put the brakes on your colon.
According to one study, constipation affects 17% of people with low thyroid hormone, compared to 10% of people with normal thyroid levels (6).
In this study, 20% of people with hypothyroidism said their constipation was getting worse, compared to only 6% of normal-thyroid individuals (6).
While constipation is a common complaint in patients with hypothyroidism, it's uncommon for constipation to be the only or most severe symptom (24).
If you experience constipation but otherwise feel fine, try these 13 home remedies before worrying about your thyroid.
If they don't work, your constipation worsens, you go several days without passing a stool or you begin having stomach pain or vomiting, seek medical advice.
Summary: Most people with constipation don't have hypothyroidism. However, if constipation is accompanied by other signs of hypothyroidism, your thyroid may be the cause.
10. Heavy or Irregular Periods
Both irregular and heavy menstrual bleeding are linked to hypothyroidism.
One study showed that about 40% of women with low thyroid hormone experienced increasing menstrual irregularity or heavy bleeding in the last year, compared to 26% of women with normal thyroid levels (6).
In another study, 30% of women with hypothyroidism had irregular and heavy periods. These women had been diagnosed with hypothyroidism after other symptoms had caused them to get tested (25).
Thyroid hormone interacts with other hormones that control the menstrual cycle, and abnormal levels of it can disrupt their signals. Also, thyroid hormone directly affects the ovaries and uterus.
There are several problems besides hypothyroidism that can cause heavy or irregular periods. If you have irregular or heavy periods that disrupt your lifestyle, consider talking with a gynecologist before worrying about your thyroid.
Summary: Heavy periods or irregular cycles that are worse than usual could be caused by a medical condition, including hypothyroidism. It's best to talk to a gynecologist about them.
The Bottom Line
Hypothyroidism, or low thyroid, is a common disorder.
It can cause a variety of symptoms, such as fatigue, weight gain and feeling cold. It can also result in problems with your hair, skin, muscles, memory or mood.
Importantly, none of these problems are unique to hypothyroidism.
Yet if you are having several of these symptoms or they are new, worsening or severe, see your doctor to decide if you need to be tested for hypothyroidism.
Fortunately, hypothyroidism is generally treatable with inexpensive medications.
If your thyroid hormone levels are low, a simple treatment could greatly improve your quality of life.