Hypothyroidism

Alternative names: Underactive thyroid gland

Hypothyroidism is a condition in which the thyroid gland does not make sufficient thyroid hormone to meet the body's requirements.  Caused in almost all cases by autoimmune disease, the result is that the immune system goes awry and begins gradually to destroy the thyroid gland.  This process is not usually associated with thyroid gland discomfort but may cause the gland to enlarge or shrink in size.

There are three types of hypothyroidism:

1. Primary hypothyroidism: The most common type, in which the thyroid doesn't produce enough thyroid hormone.
2. Secondary hypothyroidism: Occurs when the pituitary gland does not release enough of thyroid-stimulating hormone (TSH) that prompts the thyroid to manufacture thyroid hormone.
3. Tertiary hypothyroidism: Results from a malfunction of the hypothalamus, the part of the brain that controls the endocrine system.

The thyroid gland (orange) is located at the lower front of the neck below the larynx / Adam's apple (dark gray).

The thyroid gland is located at the lower front of the neck and produces and stores hormones that are essential for the function of every cell in the body.  These hormones help regulate the heart rate, blood pressure, body temperature, oxygen usage, digestion, neuromuscular function, metabolism, and growth.

Hypothyroidism is one of the most common chronic diseases.  It occurs when the thyroid gland fails to produce or secrete as much thyroxine (T4) and triiodothyronine (T3) as the body needs.  About 14-20 times as much T4 as T3 is normally produced; T4 contains four iodine atoms, and is converted to the more active T3 form (with three iodine atoms) in the liver, brain, and other tissues.  Selenium and zinc play crucial roles in this conversion process, so any deficiency can cause a conversion problem.

Incidence; Causes and Development; Contributing Risk Factors

Hypothyroidism is relatively common.  It affects between 1 in 100 to 3 in 100 women of child-bearing age.  It is more common in women than in men, and it becomes more common with age.  Hypothyroidism occurs in up to 5 to 10% of older women; up to 20% of women over 60 have evidence of hypothyroidism.

Hypothyroidism is usually caused by an autoimmune disease (Hashimoto's thyroiditis), but may also be caused by radiation therapy, thyroid surgery, or certain medications.

Another common cause of hypothyroidism is the treatments used for hyperthyroidism (overactive thyroid), namely radioactive iodine or anti-thyroid medications.  These often lead to permanent failure of the thyroid gland after a number of years.  Approximately 50% of patients treated with radioiodine, and many treated with antithyroid drugs, eventually develop hypothyroidism and should be tested about once a year.

Less common causes of Hypothyroidism include:

• Inherited thyroid disease (defective or non-existent thyroid gland)
• Iodine deficiency
• Pregnancy
• Pituitary gland disorder, whereby it does not produce sufficient thyroid stimulating hormone

Hypothyroidism tends to run in families.  If you have a history of either hypothyroidism, or paradoxically, hyperthyroidism in your family, it increases the chance that you may someday develop the condition.  However, except for a few rare disorders, hypothyroidism is not transmitted in a typical dominant or recessive manner.  If you have a strong family history of underactive or overactive thyroid disease, you should mention this to your physician.

Signs and Symptoms

Symptoms may not appear until years after the thyroid has stopped functioning, and they are often mistaken for signs of other illnesses, or menopause, or aging.

Hypothyroidism slows metabolism and affects essentially every system in the body.  Symptoms include generalized fatigue, weight gain, thinning (brittle) hair, dry scaly skin, thin nails that break easily, constipation, alterations in menses, aching muscles, and slow heart rate.  You may notice changes in behavior, such as decreased ability to concentrate, reading and calculating are more difficult, and you may experience decreased interest in personal relationships or work.  Hypothyroidism can cause or worsen depression.

Other symptoms include loss of appetite, painful pre-menstrual periods, muscle weakness, a yellow-orange coloration in the skin (particularly on the palms), yellow bumps on the eyelids, hair loss (including eyebrows), recurrent infections, depression, slow speech, lowering of the voice, premature aging and drooping swollen eyes.

Diagnosis and Tests

Hypothyroidism is more common than is typically diagnosed.  It is possible to have some laboratory values be returned in the normal range when you have low thyroid symptoms.  Oral temperatures during the day of less than 98.0°F (36.7°C) are very suspicious.

Diagnosis involves a simple blood test which measures your thyroid hormone (thyroxine or T4) and TSH (Thyroid-stimulating hormone) levels.  An elevation of TSH is a very sensitive index of reduced thyroid function.  Somewhat like the thermostat in your home, when thyroid hormone levels fall, TSH (the furnace) is switched on to stimulate the thyroid gland.  When thyroid hormone levels are low for a long time, TSH levels remain high.  Thus, hypothyroidism is characterized by a TSH level that is above the normal range and a thyroxine level that is below or at the low end of the normal range (everyone's set point is a little different).  Your physician can assist in the interpretation of these results, or you may wish to see a physician (an Endocrinologist) who specializes in hormonal disorders.

Some patients with hypothyroidism have problems converting T4 to T3.  Unfortunately, many doctors don't address this problem, and some won't even look at the T3 levels on a blood test, whereas others will prescribe synthetic T3 or natural thyroid hormone.  The bottom line is that few doctors will try to find the underlying cause of any T4-to-T3 conversion problem, which should be the goal of any effective natural treatment protocol.  The answer may be a simple and easily-correctable mineral deficiency such as selenium or zinc.

Treatment and Prevention

A medication called L-Thyroxine (L-T4) is used to replace the missing thyroid hormone.  Some preparations also include a second form of thyroid hormone, tri-iodothyronine (L-T3).  These hormones are chemically identical to those made by your own thyroid gland.  Consequently, when the correct doses are prescribed and restore your metabolism to normal, the treatment is not accompanied by side-effects.  The medication is in the form of a tablet, taken once a day.  Taking too much thyroid hormone will, of course, speed up metabolism and can cause rapid or irregular heart rate and loss of calcium from the bone.  However, excess thyroid hormone levels are unlikely to occur when the treatment is carefully prescribed and monitored.

Various brands of the synthetic T4 thyroid hormone Levothyroxine, also known as L-thyroxine.

When hypothyroidism is diagnosed, most doctors will prescribe thyroid medication and many use Synthroid (T4).  However, a recent blinded study demonstrated that T4 and T3 in combination produced greater benefits than T4 alone, especially in the area of mental functioning.

Hypopituitarism (low functioning pituitary) and hypothyroidism (low functioning thyroid) can both result in deficient production of T4, which is the raw material the body uses to produce the active thyroid hormone T3.  Your doctor should be able to help determine which medications are best for you.

The treatment of choice preferred by conventional doctors is T4 (Synthroid) because of its long half-life in the body (which helps provide steady T3 levels), once-a-day administration, and effectiveness in the treatment of such cases.  Patients with hypopituitarism and hypothyroidism may, however, suffer with Wilson's Syndrome at the same time.  In such cases, T4 therapy may not be adequate because impaired conversion of the T4 to the active compound T3 may prevent sufficient normalization of body temperature patterns and, in some cases, can even feed the vicious cycle of Wilson's Syndrome.  The simultaneous use of T4 with T3 may be the best approach for hypothyroidism, especially if Wilson's Syndrome is suspected.  Many doctors prefer using the standard T4/T3 combination found in desiccated thyroid products such as Armour thyroid and other generic brands.  Additional adjustments in the T4/T3 ratio can be made to meet the needs of individual patients.

Aside from taking a daily tablet, containing L-thyroxine, you should not have to change your lifestyle.

Is there a way to prevent hypothyroidism?  Iodine deficiency can cause hypothyroidism but this is very unlikely in North America where the iodine supply is abundant.  There are no other preventative measures you can take to avoid hypothyroidism.

Prognosis; Complications

The underlying cause of hypothyroidism is not reversible.  However, the consequences of hypothyroidism can be treated very effectively by taking thyroid hormone replacement medication.  The dose of thyroid hormone can be carefully regulated so that your body's metabolism is restored to normal.  You should have your blood tested at least once a year, or more often if necessary, to be certain that the thyroid hormone dose you are taking is satisfactory.

Recognition and proper daily treatment of low thyroid function using thyroid hormone replacement therapy will result in resolution of deficiency symptoms usually beginning within the first month of therapy and reaching a maximum at 6-12 months of treatment.  Nevertheless, it is probable that the patient will require thyroxine replacement for the rest of his or her life.

Problems with the thyroid can be the cause of many recurring illnesses and fatigue.  Hypothyroidism can cause:

• Goiter
• Heart disease
• Depression and slowed mental functioning
• Infertility
• Birth defects
• Peripheral neuropathy
• Carpal tunnel syndrome
• Raynaud's phenomenon
• Myxedema
• Digestive problems: hydrochloric acid production is reduced, resulting in malabsorption of nutrients, undigested proteins, and digestive complaints
• Significantly increased cholesterol and homocysteine levels: it is implicated in about 10% of patients with high cholesterol levels

Correcting hypothyroidism can lead to a 30% drop in cholesterol and homocysteine levels.