The thyroid is a small butterfly-shaped gland located on either side of the windpipe. The gland produces and releases hormones that regulate the body's metabolism, according to MedlinePlus.
Hyperthyroidism is a condition in which the thyroid gland produces an excess amount of thyroid hormones. This abnormal glandular activity over-stimulates the patient's metabolism, which can lead to unexpected and involuntary weight loss, nervousness, irregular heartbeat, irritability and sweating.
Causes of Hyperthyroidism
In more than 70 percent of cases, the cause of hyperthyroidism is a condition known as Graves' disease, according to the American Thyroid Association. This ailment is caused when bloodstream antibodies over-stimulate the thyroid and cause it to secrete too much thyroid hormone.
Toxic nodular goiter, or multinodular goiter, is another condition that can cause hyperthyroidism. This involves the growth of nodules on the thyroid itself that increase the gland's activity and cause abnormal and excessive secretions of the hormone into the bloodstream.
Thyroiditis is a third possible cause. This is usually a temporary condition brought about by a viral infection or immune system problem. It can also be caused by an overdose of thyroid hormone pills.
Level of Incidence
Hyperthyroidism affects around 1 percent of the American population, but it appears in women much more frequently, around 5 to 10 times more than in men, as noted by FamilyDoctor.org. This is because Graves' disease, the main cause of hyperthyroidism, is a hereditary condition, occurring more often in young women than men. In its least serious forms, hyperthyroidism may not bring out any symptoms. In most cases, however, symptoms do appear, and these can frequently be disabling or even life-threatening.
Symptoms of Hyperthyroidism
This condition causes the body's metabolism to speed up, according to MedlinePlus, a service of the National Institutes of Health website. Therefore, some of the most commonly associated symptoms include anxiety, heartbeat irregularity, hand tremors, irritability, increased perspiration, difficulty sleeping, muscular weakness and frequent bowel movements. Some patients will develop a goiter due to the swelling of the thyroid gland in the neck. Women's menstrual periods may occur less frequently. Weight loss may occur unexpectedly, even with a good appetite.
Relationship Between Thyroid and Weight
The relationship between body weight, metabolism and thyroid disease is complicated, according to the National Endocrine and Metabolic Diseases Information Service. A patient's basal metabolic rate, or BMR, is determined by measuring how much oxygen the body uses while it is at rest. Individuals with non-functional thyroid glands had low BMRs, while those with overactive thyroids had high BMRs. Later tests showed that these were due to the level of thyroid hormones in the bloodstream. However, these days, most doctors do not use BMR as a basis for evaluation because it can be affected by several other factors beyond thyroid hormone levels.
Hyperthyroidism and Weight Loss
Even though the BMR cannot provide the whole story about the relationship between weight and thyroid, it still has its uses. Fluctuations in the BMR are associated with changes in the calories the body uses compared with what the patient eats. This is known as the energy balance. Changes in thyroid levels cause changes in the BMR, thus altering energy balance and body weight.
Patients with hyperthyroidism have an elevated BMR, and many experience weight loss as a result, as noted by the American Thyroid Association. In fact, the severity of excess thyroid activity is directly related to the likelihood of weight loss as well as the amount of body mass lost.
Therefore, a serious case of hyperthyroidism increases the patient's BMR, which in turn leads to increased caloric requirements. If the patient does not consume enough calories to match these elevated requirements, weight loss occurs.
However, because hyperthyroidism also boosts the appetite, some patients may actually gain weight, depending on whether they match the altered capacity of their metabolism.