Thyroid dysfunction is highly prevalent in the United States, affecting 3.7% of Americans according the the 1997-2002 National Health and Nutrition Examination Survey (NHHES).
Many more people experience "subclinical" hypothyroidism - when the thyroid blood values appear "normal" but hypothyroid symptoms remain.
One missing link in the thyroid debate is the impact of stress.
Stress affects thyroid function in a variety of ways, from appropriate signaling and hormone binding, to actual T3 (active thyroid hormone) conversion and impaired detoxification of inactive hormones (like reverse T3) that can gunk up things.
- High cortisol slows conversion of inactive T4 into active T3 by affecting the enzyme responsible.
- Chronic stress suppresses the pituitary gland which is responsible for releasing thyroid stimulating hormone (TSH) which then leads to T4 and T3 release.
- Not all T4 is converted to active T3. Some T4 is converted to T3 Sulfate (T3S) and triiodothyroacetic acid (T3AC)which are inactive intermediates. The intermediate hormones require action by bacteria in the gut to convert them into active T3! Stress interferes with gastrointestinal integrity, leading to bacterial imbalances, that over time can deplete active T3 production!
- High levels of cortisol put stress on the liver's ability to detoxify - as cortisol itself is detoxified by the liver. T4 is also converted to an irreversibly inactive form of T3 called "reverse T3" (rT3). rT3 is also detoxed by the liver. With chronic levels of stress, the body may become inefficient at clearing out inactive rT3. rT3 interferes with normal thyroid hormone activity. This is one reason why blood levels of T3 and TSH can be normal, yet dysfunction could still be present, in part, due to stress!
Molecules morph in and out of active forms. Proteins bind to the hormones affecting their activity. Even the receptor sites are highly regulated. It's a beautiful system to think about, yet a frustrating system to "treat".
Stress is just one example of the physical, psychological, and chemical factors involved in thyroid health. The body is a series of interconnected webs of activity. This way, the body can pull from multiple streams of resources when certain systems become overloaded. Too much stress, over time, deteriorates these streams, leading to hypothyroidism.
While stress may be an important missing link to thyroid dysfunction, remember that it's just one part of a much larger web.