At least 27 million Americans have a thyroid problem, but don't know it yet.

The thyroid -- a butterfly-shaped gland located in the neck -- is the master gland of metabolism. When your thyroid doesn't function, it can affect every aspect of your health -- and in particular, weight, depression and energy levels. Hypothyroidism -- an under-active (hypo) thyroid -- is by far the most common thyroid condition, and is more common in women, affecting as many as one in five women at some point in their lives. Take the thyroid test-->