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Too little thyroid hormone can make you feel like you have no energy.
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Sometimes you might lack energy or your body may seem cold even though the room is warm. You might think that you're just "out of sorts," but if this happens regularly, you could have a relatively common disorder called hypothyroidism, which often causes fatigue and the sensation of coldness. Hypothyroidism develops when the thyroid gland doesn't make enough thyroid hormone, a disorder found in nearly 5 percent of the U.S. population over the age of 12.
The thyroid is a small gland at the front of your neck, just below the larynx, or voice box. Although it weighs less than 1 oz., the thyroid plays a central role in regulating the functions of all your cells. It produces two closely related thyroid hormones, called T3 and T4. Although chemically quite similar, T4 is converted into T3 and is a more active form of the hormone.
Your body needs thyroid hormone for many cellular processes, including cell division, which is especially important for a child or adolescent who is still growing and developing. It also increases the metabolic rate of most cells, including nerve cells, heart muscle cells and cells in the reproductive organs. The metabolic rate is the speed at which a cell uses energy. Thyroid hormone boosts the cell's ability to use oxygen and nutrients, especially carbohydrates and fats.
Hypothyroidism develops when the thyroid produces too little of one or both of the hormones T3 and T4, resulting in a low level of oxygen and nutrient usage throughout the body. According to research published in October 2011 in "Current Opinion in Endocrinology, Diabetes, and Obesity," thyroid hormone also dilates the blood vessels that supply your heart and muscles, helping boost your heart rate and muscular activity when you move or exercise.
In hypothyroidism, because thyroid hormone is low, blood flow to your heart and muscles increases slowly when you want to be more active, making you feel tired and sluggish. Thyroid hormone also stimulates enzymes in your cellular mitochondria -- the power producers of cells -- that produce heat and enhance other cellular functions that are heat-generating. When thyroid hormone levels are low, these enzymes and other processes are slowed, making you feel cold, even if your environment is warm.
Several conditions can cause a low production of thyroid hormone and lead to hypothyroidism, including an autoimmune disorder called Hashimoto disease, in which immune cells attack the thyroid and lessen its ability to make thyroid hormone. Several other problems, collectively called thyroiditis, may also inflame the thyroid gland and cause hypothyroidism. Surgical removal of a cancerous or diseased thyroid, or thyroid irradiation for an overactive thyroid are responsible for some cases of hypothyroidism.
Hypothyroidism may also be caused by a problem in the pituitary gland, a condition called secondary hypothyroidism. In this case, decreased production of the pituitary hormone, called thyroid stimulating hormone, which stimulates the thyroid, is responsible for low thyroid hormone. If your doctors suspects your lack of energy and sensation of cold may be due to hypothyroidism, he will order tests to help determine its cause and the best treatment.
In many cases of hypothyroidism, a doctor will recommend taking a synthetic form of thyroid hormone that contains T4, which your body then converts to the more active form, T3. In most people, this treatment is successful in bringing blood levels of the hormone back to normal, increasing energy and getting rid of the sensation of being constantly cold. Occasionally, a doctor may find a person responds better to a prescription natural form of thyroid hormone, made from pig thyroid. Extracts from thyroid glands are also available at health-food stores, but you should avoid these because they are not regulated by the U.S. Food and Drug Administration, so you can't be sure of their purity and dose.
Like many disorders of the endocrine glands, hypothyroidism can be a complicated condition and should only be managed by a qualified health care professional, such as a family practitioner or a specialist in internal medicine or endocrinology.