Shaped like a butterfly and nestled just below the larynx (Adam's apple), the thyroid gland is a key player in the body's metabolism. Disturbances in thyroid function can occur at any age, but they most commonly occur after the age of 40.

Since it can take many years before symptoms of either hypo- (underactive) or hyper- (overactive) thyroidism appear, here's what women (they develop thyroid disorders at a rate of almost eight times that of men) should know about thyroid dysfunction.

1. A genetic condition called Hashimoto's thyroiditis is the most common cause of hypothyroidism.
This thyroid disorder occurs when the body produces antibodies against itself. These antibodies prime the thyroid gland to see itself as "foreign," setting up a state of chronic inflammation, which interferes with the secretion of T4 (also known as thyroxine) and T3 (triiodothyronine), hormones that help regulate the body's metabolic rate. When your T3 and thyroxine levels are low, you may gain weight, feel lethargic and experience difficulties with memory.

2. An overactive thyroid can be mistaken for an emotional disorder.
Symptoms of hyperthyroidism can include anxiety, mood swings, irritability and depression. There are two main causes of hyperthyroidism:

• Graves' disease. As with Hashimoto's thyroiditis, Graves' disease is a genetic disorder in which the body produces an antibody against itself, but in this case, the antibody prompts the gland to overproduce rather than underproduce thyroid hormone, explains Dr. Jerald Bain, an endocrinologist at Mount Sinai Hospital in Toronto.

• Subacute thyroiditis. Probably caused by a virus, this low-grade condition causes inflammation in the thyroid gland, which triggers the release of thyroid hormone. "This form of hyperthyroidism has a limited life span," notes Bain, "and it may or may not be symptomatic."

3. Treatment for thyroid disorders depends on whether you want to produce more or less thyroid hormone.
If you have hypothyroidism, thyroxine replacement therapy will help balance hormone levels. But whether to take synthetic thyroid hormone, which is most like the human hormone and which most doctors prescribe, or to opt for what's called "natural" (or "dessicated") thyroxine, which comes from cows, is up for debate.

To treat an overactive condition such as Graves' disease, doctors usually opt for antithyroid drugs such as propylthiouracil or methimazole (Tapazole), but if these don't work, radioactive iodine is another option. Radioactive iodine is taken up by the thyroid gland, reducing its function, thereby limiting hormone production. Doctors treat subacute thyroiditis with an anti-inflammatory agent, but because inflammation can damage the gland, they typically add thyroxine therapy while the gland repairs itself.

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4. Thyroid cancer can usually be treated successfully.
People who received radiation therapy to the head during infancy or childhood and those who have developed a goitre as a result of either too little or excessive amounts of iodine are at increased risk of developing thyroid cancer. A hallmark of thyroid cancer is a lump or swelling in the front of the neck. Diagnosis is made following analysis of a small amount of tissue from the thyroid gland. Treatment consists of destroying the gland with radioactive iodine or surgically removing it. Either way, people will require lifelong thyroxine therapy to compensate for the loss of their natural hormones.

5. Postpartum thyroiditis, a thyroid dysfunction following childbirth.
• It may be confused with postpartum blues or the "tired mother" syndrome.

• An estimated 50 per cent of women in their childbearing years who develop an episode of thyroiditis do so as a result of a recent pregnancy.

• It is usually transient and doesn't typically require treatment.

• New mothers should have their thyroid function checked to ensure hormone levels are in balance.

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