THYROID: THE BODY’S INTERNAL ENERGY SOURCE
If you are feeling tired with low energy, feeling cold, have thinning hair or gaining weight you should read on. For a structure that weighs less than 1 ounce, the thyroid gland plays a key role in our metabolism. The main role of the thyroid is to produce thyroid hormone, which is the driver of metabolism.
Thyroid hormone works at the level of cell nucleus to influence gene expression for many chemical reactions that influence multiple metabolic processes. The work of almost every vitamin and mineral used by our body is complemented and enhanced by adequate amounts of thyroid hormone.
The pituitary gland in the brain sends a chemical called thyroid- stimulating hormone (TSH) that tells the thyroid to make more hormone. The thyroid produces predominantly 2 types of thyroid hormone, triiodothyronine (T3), and thyroxine (T4) with the number based on the number of iodine molecules attached to the hormone. The thyroid makes 80% T4 and 20% T3.
Some of the functions of thyroid hormone include temperature regulation, metabolism, cerebral function, and maintaining and producing energy. In other words, thyroid determines how we produce energy, how we think, and how we process food and the calories that we eat.
If someone’s thyroid function is impaired, all these processes will be affected. The resulting symptoms include fatigue, memory loss, coldness, low energy, thinning hair, dry skin, constipation and weight gain. The abnormal metabolism leads to high cholesterol. Body functions are impaired so there may be symptoms of irritable bowel and irritable bladder. Men may experience erectile dysfunction and women may experience menstrual irregularities. In other words, those with thyroid problems feel lousy.
Thyroid status is primarily measured by lab tests. When thyroid function is impaired, this is called hypothyroidism. This gives it a medical sound though is the Latin way of saying low thyroid. There are different types of hypothyroidism. Subclinical hypothyroidism occurs when the TSH is elevated while the thyroid hormone levels T3 and T4 are normal. The normal thyroid levels suggest there is no problem but the elevated TSH suggests that the brain seems to think it needs to work harder to stimulate the thyroid.
There is controversy in the literature whether subclinical hypothyroidism needs to be treated. This is because some studies indicate that there is increased heart disease and higher mortality among those with this condition while other studies show no such relationship. One study showed a 2.2 increased risk of heart disease with subclinical hypothyroidism, or more than double the risk.
Primary hypothyroidism is manifest by elevated TSH while thyroid hormone levels are decreased. There is near unanimous agreement that this condition should be treated with thyroid hormone replacement. The question then becomes what type of thyroid hormone will be used. The most common thyroid used is levothyroxine (Synthroid), which is T4. The problem is that there are patients that do not feel any better when taking only T4. Another option is to take a thyroid preparation, which has a combination of T3 and T4. The most common of these is desiccated thyroid, which is porcine derived, though a compounded combination of synthetic T3 and T4 is available.
Secondary hypothyroidism occurs when there is poor conversion of T4 to T3. Some of the factors that predispose to this are stress, fasting, illness or old age. This is more challenging to diagnose because the TSH and T4 are normal. The T3 is decreased so it is necessary to check this. The reason that some patients feel lousy when taking T4 is that they are not able to convert T4 to T3. As noted above, the thyroid gland makes predominantly T4. However, T3 is much more active at the cellular level so to get the metabolic benefit of thyroid, converting T4 to T3 is essential. So for this condition, treating with a combination of T4 and T3 is essential.
Tertiary hypothyroidism occurs when the receptors for thyroid function are insensitive to thyroid hormone. The hormone is present but is unable to effect action at the cellular level. Therefore, one will have symptoms of low thyroid while their thyroid lab studies are normal. Because of the normal lab values, this is very difficult to diagnose. Due to the thyroid resistance, a higher dose of thyroid hormone may be required to achieve therapeutic benefit.
There are health risks associated with untreated hypothyroidism. In a group of elderly adults, low T3 was associated with increasing disability, decline of global function and increased mortality while those who survived to at least age 89 had the highest T3 levels. In a study, a disproportionate number of adults with congestive heart failure had low T3 levels. The increased risk of heart disease with hypothyroidism is similar to smoking and high cholesterol. Also, those with hypothyroidism have increased risk of cognitive deficits.
For those with thyroid dysfunction, thyroid replacement can dramatically improve quality of life as the symptoms resulting from the dysfunction improve. However, thyroid replacement is controversial because of the potential problems that may result. One potential problem is cardiac arrhythmia. This results from thyroid’s stimulant effects on cardiac tissue. If the dose is adjusted slowly with symptoms and response monitored, palpitations can be minimized and avoided.
A common misconception is that thyroid replacement is osteoporosis. Hyperthyroidism or excess thyroid may predispose one to osteoporosis. However, multiple studies have shown that thyroid replacement does not cause osteoporosis. It should also be noted that low T3 is associated with vertebral fractures related to osteoporosis so thyroid replacement can actually prevent these fractures.
In summary, thyroid hormone is essential for metabolism, brain function and general well being. While the thyroid is generally assessed by looking at lab values, there are certain conditions that cause misleading labs. The key to successful treatment with the best outcomes for one with thyroid dysfunction is to treat not just the labs but to treat the patient and the symptoms.