The thyroid is one of the largest endocrine glands in the body. This gland is found in the neck inferior to (below) the thyroid cartilage (also known as the Adam's apple in men) and at approximately the same level as the cricoid cartilage. The thyroid controls how quickly the body burns energy, makes proteins, and how sensitive the body should be to other hormones.
The thyroid participates in these processes by producing thyroid hormones, principally thyroxine (T4) and triiodothyronine (T3). These hormones regulate the rate of metabolism and affect the growth and rate of function of many other systems in the body. Iodine is an essential component of both T3 and T4. The thyroid also produces the hormone calcitonin, which plays a role in calcium homeostasis.
The thyroid is controlled by the hypothalamus and pituitary. The gland gets its name from the Greek word for "shield", after the shape of the related thyroid cartilage. Hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid) are the most common problems of the thyroid gland.
In recent decade, there has been an increased incidence of thyroid problems. In fact, more than 20% of women and 10% of men have low thyroid function.
Here are the most common symptoms of low thyroid:
The thyroid is extremely sensitive to influences from diet, lifestyle and the environment. Low levels of selenium reduce the function of the thyroid and contribute to depression. And because our soil is depleted of selenium, we get much less in our diet than we did in previous decades.
Environmental chemicals including dioxins (like PCBs), heavy metals (like mercury) as well as chlorine, fluoride and bromine also negatively impact the function of the thyroid gland and should be avoided.
American Thyroid Association (Thyroid Information and professional organization)