The symptoms of an underactive thyroid vary from person to person depending on the level of deficiency. These symptoms take a few years to fully develop and a person may live for years without even knowing that they have thyroid health problems. Fatigue and an increase in body weight are among the first symptoms and most people simply assign them to aging.

1. Increase in body weight
Packing on a few pounds is among the first reported symptoms of thyroid problems because the condition tends to slow down a person's metabolism. When someone has hypothyroidism, their thyroid hormone levels are low, and instead of turning calories into energy, a person's basal metabolic rate drops. This is the reason why most people gain some weight when diagnosed with underactive thyroid even if they eat as usual or less.
2. Feeling exhausted
Extreme tiredness is a frequent sign of an underactive thyroid. If you feel tired often despite a good night sleep, speak to your physician about possible reasons. The thyroid gland controls the levels of energy that we have and regulates the time when we're supposed to feel ready to sleep. People an with overactive thyroid tend to feel jittery and anxious and those with an underactive thyroid feel the opposite – sluggish and tired.
3. Feeling constipated
If you're often constipated, it can be due to underactive thyroid. Hypothyroidism is among the top three reasons for severe constipation because thyroid hormone regulates gut motility. If the production of this hormone is disrupted, bowel movements change as well.
4. Puffiness
Hypothyroid patients tend to retain fluids, which often makes the face and other parts of the body such as the eyelids or ankles look swollen and puffy. This happens because of the low body temperature that is caused by thyroid dysfunction. If parts of your body look and feel bloated, it might be due to an underactive thyroid, and you should check it with your physician.
5. Intolerance to cold
When an underactive thyroid slows down a person's metabolism, it automatically makes them more sensitive to cold. Being intolerant to cold and having chills too often is commonly associated with an underactive thyroid. When the body has less energy due to system slow-down, it has less heat as well.
6. Losing hair
Damaged and brittle hair is a common symptom of an underactive thyroid. Lack of thyroid hormone affects hair growth by forcing too many hair follicles to go to a resting mode at once. This occurs with hair all over the body, not just those on the head.
7. Itching
Dry and scaly skin is also a common sign of underactive thyroid. Due to a slow metabolism, the amount of sweat that the body produces decreases, which leaves skin with no moisture, and it can soon become dry and itchy. Nails can get affected and become dry and ridgy as well.
8. Hoarse voice
A hoarse voice is a symptom, not a disease. People have reported hoarseness due to many reasons including anatomic, neurologic, functional, as well as environmental sources. A few reasons such as voice abuse or laryngitis are mostly benign, but there are more serious reasons for hoarseness that can even endanger your life.
9. Problems with muscles and joints
An underactive thyroid can cause parts of the body to become numb and even painful. This commonly includes the arms, legs, feet, and hands. When someone suffers from hypothyroidism, the condition turns their metabolism to a catabolic state, meaning that the body breaks down itself for energy. If this happens, the strength decreases and a person can feel weak. Muscle breakdown may cause pain and swelling.
A decrease in thyroid hormone production can affect the nerves that send signals between the brain and other parts of the body. This is why some people feel twinges in hands or legs. Experiencing “inexplicable” tingles is a good reason to visit your doctor.
10. Hypertension
Both high and low blood pressure are associated with thyroid problems, but high blood pressure or hypertension is three times more common in people with hypothyroidism. Experts assume this happens because an underactive thyroid slows down your heart beat, which affects the intensity of pumping and the flexibility of blood vessels.
11. Increased cholesterol
Increased levels of the “bad” or LDL cholesterol that can't be fixed with diet, exercise, or drugs have been connected to an underactive thyroid. The excess of low density lipoprotein should be a cause for concern in people diagnosed with underactive thyroid because if left untreated, it can lead to even more problems such as heart failure.
12. Mood swings and mental fogginess
Memory problems are often associated with aging and lack of sleep, but a decrease in the production of thyroid hormone can cause these problems too. This is because thyroid hormone regulates the metabolism in every part of the body, including brain. This means that an underactive thyroid can lead to forgetfulness, problems with concentration, and more serious memory impairment. Studies have shown that an underactive thyroid especially affects so-called verbal memory.
Fortunately, these disorders are not for life. According to research, as soon as a person starts treating their hypothyroidism, the symptoms decrease or disappear as well.
13. Decreased libido
Hypothyroidism can cause a decrease in sexual appetite. Together with other thyroid-related symptoms such as an increase in body weight and muscle stiffness and pain, a person can lose a part or all sexual desire.
14. Irregular menstrual bleeding
Heavy periods occur in one in four women. An underactive thyroid is one of the more common causes of heavy or irregular menstruation. If the production of thyroid hormone is decreased, periods tend to last longer and a woman has more cramps. With a lack of thyroid hormone, the ovaries produce less progesterone, a hormone responsible for regulating menstrual flow. Without progesterone, blood doesn't have enough coagulation power to prevent heavy flow. Hypothyroidism also tends to make periods closer together than they are in women without thyroid problems.
15. Difficulties conceiving
Women with underactive as well as overactive thyroid may find it harder to get pregnant than healthy women. When the thyroid gland can't make enough thyroid hormone, it affects ovulation – the release of eggs from a woman's ovaries – an issue that affects fertility.
Several underlying causes of underactive thyroid such as pituitary or autoimmune conditions may affect fertility and cause difficulties in getting pregnant. Finding the right treatment for your underactive thyroid also means you'll have a bigger chance to conceive a baby.
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