In essence, the thyroid gland’s main function is to control the “speed” of body functions. If it is too slow, as with hypothyroidism (low thyroid), many body systems slow down (see table below). Symptoms of hypothyroidism are often non-specific, meaning the symptoms could also be caused by a range of other health conditions. In extreme cases, severe and prolonged hypothyroidism can lead to anemia, low body temperature, and heart failure. Getting proper medical diagnosis is essential if you have symptoms that persist.
The thyroid gland makes two different hormones – T4 and T3. About 90 per cent of its production is T4. In healthy people, almost all the T4 changes to T3 in various body tissues. The rest of the body really needs this form to function properly. Iodine, an element consumed through food and water, is a necessary part of T4 and T3.
When the amount of thyroid hormone secreted by the gland is too low, the body naturally tries to increase the amount of thyroid hormone made by the thyroid gland. In some cases the gland responds by increasing in size, forming a goiter (an enlargement of the gland which may be seen or felt at the front of the neck).
A number of blood and physical tests can indicate if symptoms are due to thyroid problems or another condition. The most useful blood screening and monitoring marker of thyroid function is thyroid-stimulating hormone (TSH). TSH is an indirect marker. It does not measure thyroid hormone in the blood, but instead shows pituitary gland response to low levels of thyroid hormone. (The pituitary is a small gland in the brain.) TSH sends a message to the thyroid gland to make more thyroid hormone.
In some cases, it can be useful to measure hormone levels directly. A blood test can detect actual T4 and T3. If a person has other medical illnesses, another test can measure reverse T3, which may form but is inactive in the body.
In most cases, the TSH will show how well the thyroid is working. It will also accurately monitor whether treatment is working as it should.
Treatment for hypothyroidism almost always consists of taking replacement hormone. Usually, synthetic T4 is used, with Synthroid™ and Eltroxin™ being the most commonly prescribed. The body converts replacement T4 to the more useful T3. When this happens properly, TSH returns to normal range and symptoms disappear.
Interestingly, recent research and experience shows that simply using synthetic T4 to normalize TSH may not address all the problems.
Much debate exists about the correct ‘normal range’ of TSH. The normal range quoted for TSH by our standard laboratories is 0.5 to 5.5 (or 6.0) umol/L. This is very broad. Some recent studies have shown that more benefits may come when TSH is between 0.5 and 2.0 umol/L. This level appears to help lower cholesterol and protect from heart disease. Someone who is very proactive or still has symptoms might ask about adjusting therapy to get TSH into the lower range.
In some people, TSH may be quite slow to respond to changes in thyroid function. Several weeks of thyroid hormone are generally stored in the thyroid. If the gland is damaged, problems may not show up for a while. If this is suspected, testing again after several weeks is wise.
On the other hand, blood test markers of low thyroid sometimes show as high TSH, but with no symptoms. The thyroid gland starts to make more T4 when stimulated, but eventually cannot keep up. Hypothyroid symptoms will develop at this point.
Sometimes, the problem lies in changing T4 to T3. In this case, measurable levels of TSH and T4 may be normal. However, if the body is not getting enough T3, symptoms may continue. This is particularly true for someone who is dieting. Fewer calories cause less T4 to change to T3. For the same reason, correcting hypothyroidism with T4 replacement alone will almost never result in weight loss.
Considerable excitement currently exists in the media about the ability of iodine to treat low thyroid conditions. However, a lack of iodine is almost unheard of in North America – ever since salt became iodized. Iodine is needed only in very small amounts. Eating any salt, whether table salt or salt used in cooking or processing foods, will supply the necessary amount for thyroid function. While sea salt is not iodized, seaweed and kelp are very high in iodine, and sea salt may absorb it from these sources.
At one time, doctors felt confident that simply prescribing synthetic T4 replacement would solve hypothyroidism. This may still be true. However, anyone taking T4 replacement should keep the following facts in mind.
Thyroid hormone replacement must be taken carefully and consistently. That being said, an occasional missed dose will not likely cause any symptoms. T4 stays stable in the system for several days after it is missed.
Watching for the effects of thyroid overload is also necessary. This may occur:
Symptoms of too much thyroid hormone include rapid heart rate, sweating, overheating, tremor, irritability, nausea and vomiting and weight loss. This may also be dangerous for someone with heart problems. In the long term, it may also cause osteoporosis (fragile bones).
Diagnosing and monitoring thyroid disorders and their treatment is complex. Anyone with symptoms of low thyroid, whether young, old, male or female, should seek proper medical attention. They must also watch for conditions that may affect medication or other therapies.