Hypothyroidism is a condition marked by having an underactive thyroid. It is a glandular disorder where the body does not produce enough thyroid hormones to meet the body’s needs.
The thyroid gland is found in the front part of the neck, below the larynx. It has a lobe on each side of the windpipe. This endocrine gland is made up of several hormone-producing cells. Hormones help relay information to organs and tissues in the body and control several biological processes.
Hormones produced in the thyroid gland (thyroxine and triiodothyronine) help regulate metabolism in the body by controlling cellular oxidation. Many functions in the body slow down when the levels of these hormones are low. The production of thyroid hormones is regulated by another hormone produced in the pituitary gland called thyroid-stimulating hormone (TSH). This stimulating hormone is regulated by the hypothalamus in the brain.
Hypothyroidism can affect adults of any age, particularly those who are older than 60 years old. It is more common in middle-aged and older women. It can also happen among children and infants. Infants with an underactive thyroid are usually born with it.
According to a study sponsored by the American Thyroid Association and American Association of Clinical Endocrinologists, an estimated 4.6 percent of people above the age of 12 in the United States have hypothyroidism.  Most of these people are not aware. This is because hypothyroidism may not cause any symptoms in its initial stage. Typically, the condition progresses slowly and develops over several years, so even early symptoms may be dismissed as a part of aging.
As the condition progresses, more obvious symptoms start to appear, resulting in certain health problems. The symptoms that appear usually depend on the severity of hormone deficiency. If you experience any of the following symptoms, it may be a sign that you have an underactive thyroid.
Fatigue is a state of extreme or intense tiredness. While this term is usually used interchangeably with tiredness, both conditions differ. Tiredness typically resolves with adequate rest. Fatigue is persistent and remains even after getting enough rest. Sometimes it can be severe enough to make even simple tasks difficult to do.
Many underlying conditions can cause fatigue, including an underactive thyroid.  This happens because the rate of metabolism, or the use of body energy, is very low in people with hypothyroidism. Usually, this symptom can be alleviated by using daily hormone replacement tablets. In some cases, fatigue persists even after using the tablets.