The thyroid is a bow-shaped gland located in front of the neck that produces the thyroid hormones thyroxine, or T4, and triiodothyronine, or T3. The thyroid gland also produces calcitonin -- a hormone that corrects high blood calcium. The thyroid hormones directly influence calcium absorption in the intestines. Thyroid conditions that alter calcium absorption include hyperthyroidism, hypothyroidism and thyroid surgery.
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The body absorbs calcium from ingested food. Good sources of calcium include milk, yogurt, ice cream, cheese and tofu. The thyroid and parathyroid glands regulate blood calcium. When blood calcium is low, the parathyroid glands release parathyroid hormone, which breaks down bone to release calcium into the blood. When blood calcium is high, the thyroid gland releases calcitonin, which reduces the levels of calcium in the blood. Vitamin D facilitates intestinal calcium absorption, and the action of parathyroid hormone, produced by the parathyroid gland, enhances it. Parathyroid hormone also stimulates calcium reabsorption from the kidneys, but high blood calcium results in increased calcium excretion.
Hyperthyroidism and Calcium Absorption
Graves' disease -- a form of hyperthyroidism caused by an overactive immune system -- is the most common form of hyperthyroidism in the United States. Hyperthyroidism results from increased secretion of T3 and T4. It may occur as a result of increased stimulation of the thyroid gland by the brain or by increased activity within the thyroid gland itself. Symptoms associated with hyperthyroidism include intolerance to heat, sweating, rapid heart rate, weight loss, increased appetite, shakiness and difficulty sleeping. A 2008 "Seminars in Nephrology" article reports that hyperthyroidism is associated with increased urine calcium -- a condition explained by increased vitamin D receptors in the intestines. Increased vitamin D receptors result in increased vitamin D activity and, therefore, increased calcium absorption.
Hypothyroidism and Calcium Absorption
Hypothyroidism results from decreased secretion of T3 and T4. Symptoms associated with hypothyroidism include weight gain, constipation, fatigue, constipation and paleness of the skin. Hypothyroidism is associated with decreased excretion of vitamin D. The vitamin accumulates in the blood as a result of low heart rate and decreased blood flow to the kidneys. Intestinal calcium absorption increases as a result of higher levels of vitamin D.
Thyroidectomy, or thyroid removal, is a surgical intervention procedure reserved for conditions of the thyroid gland that do not respond to medical treatment. Doctors treat thyroid cancer surgically, for example. Hypothyroidism results from thyroid surgery but depends on the amount of thyroid removed; the resulting hypothyroidism also is associated with increased calcium absorption.