Setting the Pace: Thyroid & Metabolism

Hormones, from the Greek word for “excite” or “spur on,” are body chemicals that arouse and direct the behavior of other body chemicals. The influence hormones exert on physiological processes is staggeringly fast and powerful. And it is also the case that hormones virtually never act in isolation; instead, it is the interplay among various hormones that creates a network of feedback signals and mechanisms.

The thyroid and the hormones it produces, for example, are under control of a hormone called TSH (thyroid-stimulating hormone), which is produced by the pituitary gland. The pituitary gland is often referred to as the “master gland” because it regulates the activities of other endocrine glands. The pituitary gland, however, takes its orders from the hypothalamus, which decides which particular hormones the pituitary should release and when.

Also in response to direction from the hypothalamus, the pituitary gland releases other key hormones, many of them involved in reproduction, pregnancy and lactation, including: follicle stimulating hormone (FSH); luteinizing hormone (LH); prolactin, and oxytocin; as well as growth hormone (GH). LESS

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Hypothyroidism, the problem of too little, can be caused by different factors, including radiation therapy; congenital defects (1 in 3,000 births); medications; and iodine deficiency (rare in the U.S., but common in the developing world), and autoimmune disease. An example of an autoimmune cause is chronic thyroiditis, also called Hashimoto’s disease, in which the body’s immune system attacks thyroid tissue and reduces the gland’s ability to produce thyroid hormone.

Symptoms of hypothyroidism may include weight gain, dry skin, constipation, cold intolerance, hair loss, fatigue, and menstrual irregularity in women. Left untreated, hypothyroidism can lead to goiter, heart problems, depression, and damage to nerves in arms and legs. Myxedema is a rare, life-threatening condition that results from long-term, undiagnosed hypothyroidism. Symptoms include intense cold intolerance and drowsiness followed by profound lethargy and unconsciousness.

Strangely enough, hyperthyroidism, the problem of too much, can also have an autoimmune cause. In fact, More than two-thirds of all cases of hyperthroidism are caused by an autoimmune disorder called Graves’ disease. With Graves' disease, however, (unlike Hashimoto’s disease) antibodies produced by the immune system stimulate the thyroid, spurring it on to produce too much hormone.

Symptoms of hyperthyroidism may include, increased heart rate, anxiety, weight loss, sleep disturbance, tremors in the hands, weakness, bulging, red or irritated eyes, often accompanied by sensitivity to light, blurring or double-vision. Left untreated, hyperthyroidism can lead to osteoporosis and heart problems, including rapid heart rate, a heart rhythm disorder called atrial fibrillation and congestive heart failure. LESS

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Thyroid tests are typically ordered when someone has symptoms of thyroid dysfunction or when a person has an enlarged thyroid gland. TSH screening is also routinely performed in the U.S. on newborns. Often, infants with congenital hypothyroidism appear normal at birth. When hypothyroidism in infants isn't treated, even mild cases can lead to severe physical and mental development problems. If the condition is diagnosed within the first few months of life, however, the chances of normal development are excellent, which is why most states now require newborn thyroid screening.

In children and adults, however, expert opinions vary on who can benefit from screening and at what age to begin. Several organizations recommend screening for women over 50 or those at high risk for thyroid disorders, such as pregnant and postpartum women. Low levels of thyroid hormone in younger women can interfere with ovulation, which impairs fertility. Some women develop hypothyroidism during or after pregnancy; left untreated, it increases the risk of miscarriage, premature delivery and preeclampsia, a condition that results in a sharp rise in a woman's blood pressure during the last trimester of pregnancy. Babies born to women with untreated thyroid disease have a higher risk of birth defects. LESS

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