The thyroid is important to maintain health and proper weight. The thyroid is a small gland located just below the Adam’s apple in your neck. Your body has a constant feedback mechanism on all body processes. The body adjusts and makes more or less of a particular molecule as needs arise to adjust the levels of your hormones, proteins, enzymes, etc.
The hypothalamus is located just above your pituitary gland in your brain. It secretes a thyrotrophin-releasing hormone which signals the pituitary gland to make a thyroid-stimulating hormone (TSH). TSH stimulates the production of your thyroid hormones. The pituitary gland controls the rate of release of TSH to adjust to your body needs.
Thyroid and Metabolism
Thyroxine (T4) and triiodothyronine (T3) are two of the major hormones secreted by the thyroid gland. T4 is produced in greater quantity and has a minor effect on your metabolism. T4 is converted to T3 in the liver. T3 is the active hormone that controls your metabolic rate. Many factors affect the conversion of T4 to T3. Anything that affects the total amount of T3 slows down your metabolism.
T4 and T3 are bound to a protein called thyroxine-binding-globulin in your bloodstream. Very little T4 and T3 are unbound or free in the bloodstream. The unbound or free T3 is the active hormone affecting your metabolism. Not all your T4 is converted to T3. If it were, you would have too much T3 and your metabolism would be on fire, so to speak.
Some residual iodine can be recycled back to your thyroid gland after free T4 and T3 are used up. Your body converts some T4 to reverse-T3 to get rid of the excess T4. Some reverse-T3 is converted to T1 and T2 (your other two thyroid hormones) while the remainder is quickly eliminated from your body to keep it in balance. This process is the way your body rids itself of iodine over the course of the day.
Factors Affecting Metabolism
The most prevalent factors that decrease the conversion of T4 to T3 are illness or disease, stress, and starvation. Liver disease affects T4 to T3 conversion. Stress increases cortisol levels and slows down the production of T3. The body assumes that this is a survival mechanism to slow down your metabolism in times of stress.
Under normal conditions, 40% of T4 is converted to T3. During disease, stress, or starvation, the conversion of T4 to reverse-T3 increases. The normal T4 to T3 conversion goes from 40% to 20%. Stress causes your body to hold on to more reverse-T3 than it normally would in times of good health. This is not good since it affects T4 production. You end up in a loop of low T3 without the benefit of having enough replacement T4 to make up the deficiency. Your metabolism slows. You are not burning calories as you had in the past. You add fat in spite of eating less and exercising more.
Deficiency in the following vitamins and minerals affects your T4 to T3 conversion: chromium, copper, iodine, iron, selenium, zinc, vitamins’ A, B2, B6, and B12. Additionally, medications can affect your T4 to T3 conversion. Beta-blockers, birth control pills, estrogen, lithium, steroids, and a few other drugs affect the conversion of T4 to T3. Alcohol, aging, fluoride, lead, mercury, pesticides, and radiation also affect T4 to T3 conversion. Iodine absorption is affected by soy products and cruciferous vegetables. Obesity also affects your T4 to T3 conversion.
Your T4 and T3 levels are measured by your doctor as you approach your 60’s. Thyroid function may decrease with age for some. TSH is the best indicator of overall thyroid function. Tests are done for both bound and free (unbound) T4 and T3. If your doctor determines that you are producing less T4 or T3 than is appropriate for your age and health, then additional tests can be conducted.
One such test is a touch test – your doctor feels your thyroid gland for nodules. If they are present, an ultrasound scan is done to measure the size of your thyroid gland and any nodules or cysts that might be present on your thyroid gland.
Another test uses radioactive iodine. The radioactive iodine is administered into your bloodstream. Your thyroid is monitored with an imaging camera that can give your doctor a clear picture of the overall structure of your thyroid gland. Since your thyroid is divided into two sections – one on each side of your body – each section can be compared to determine healthy and unhealthy aspects of your thyroid gland. If you have a thyroid hormone imbalance that cannot be detected in your thyroid gland, your doctor may further investigate your pituitary gland.
Live Longer & Enjoy Life – Red O’Laughlin