Because T4 regulates such essential functions as heart rate, digestion, physical growth, and mental development, an insufficiency of this hormone can slow life-sustaining processes, damage organs and tissues in every part of the body, and lead to life-threatening complications.
Hypothyroidism is one of the most common chronic diseases in the United States. Symptoms may not appear until years after the thyroid has stopped functioning, and they are often mistaken for signs of other illnesses, menopause, or aging. Although this condition is believed to affect as many as 11 million adults and children, as many as two of every three people with hypothyroidism may not know they have the disease.
The thyroid gland influences almost every organ, tissue, and cell in the body. It is shaped like a butterfly and located just below the Adam’s apple. The thyroid stores iodine the body gets from food and uses this mineral to create T4 and T3. Low T4 levels can alter weight, appetite, sleep patterns, body temperature, sex drive, and a variety of other physical, mental, and emotional characteristics.
There are three types of hypothyroidism. The most common is primary hypothyroidism, in which the thyroid doesn’t produce an adequate amount of T4. Secondary hypothyroidism develops when the pituitary gland does not release enough of the thyroid-stimulating hormone (TSH) that prompts the thyroid to manufacture T4.
Tertiary hypothyroidism results from a malfunction of the hypothalamus, the part of the brain that controls the endocrine system. Drug-induced hypothyroidism, an adverse reaction to medication, occurs in two of every 10,000 people, but rarely causes severe hypothyroidism.
Hypothyroidism is at least twice as common in women as it is in men. Although hypothyroidism is most common in women who are middle-aged or older, the disease can occur at any age. Newborn infants are tested for congenital (acquired in utero (Latin)) thyroid deficiency (cretinism) using a test that measures the levels of thyroxine and TSH in the infant’s blood. Treatment within the first few months of life can prevent mental retardation and physical abnormalities. Older children who develop hypothyroidism suddenly stop growing.
Factors that increase a person’s risk of developing hypothyroidism include age, weight, and medical history. Women are more likely to develop the disease after age 50; men, after age 60. Obesity (excessively fat condition) also increases the risk.
A family history of thyroid problems or a personal history of high cholesterol levels or such autoimmune diseases as lupus, rheumatoid arthritis, or diabetes can make an individual more susceptible to hypothyroidism.
Causes and symptoms
Hypothyroidism is most often the result of Hashimoto’s disease, also known as chronic thyroiditis (inflammation of the thyroid gland). In this disease, the immune system fails to recognize that the thyroid gland is part of the body’s own tissue and attacks it as if it were a foreign body.
The attack by the immune system impairs thyroid function and sometimes destroys the gland. Other causes of hypothyroidism include:
- Radiation (the process whereby an element like radium emits rays). Radioactive (the quality some atoms have of producing energy) iodine used to treat hyperthyroidism (overactive thyroid) or radiation treatments for head or neck cancers can destroy the thyroid gland.
- Surgery. Removal of the thyroid gland because of cancer or other thyroid disorders can result in hypothyroidism.
- Viruses (very small organisms that cause disease)and bacteria (very small one-cell organisms that divide and can cause disease). Infections that depress thyroid hormone production usually cause permanent hypothyroidism.
- Human immunodeficiency virus (HIV). Among viruses, HIV, the virus that causes acquired immunodeficiency syndrome, or AIDS, may cause overt hypothyroidism. A 2004 report said that hypothyroidism occurs more often in HIV-infected patients taking highly active antiretroviral therapy (HAART).
- Medications. Nitroprusside, lithium, or iodides can induce hypothyroidism. Because patients who use these medications are closely monitored by their doctors, this side effect is very rare.
- Pituitary gland malfunction. This is a rare condition in which the pituitary gland fails to produce enough TSH to activate the thyroid’s production of T4.
- Congenital defect. One of every 4,000 babies is born without a properly functioning thyroid gland.
- Diet. Because the thyroid makes T4 from iodine drawn from food, an iodine-deficient diet can cause hypothyroidism. Adding iodine to table salt and other common foods has eliminated iodine deficiency in the United States. Certain foods (cabbage, rutabagas, peanuts, peaches, soybeans, spinach) can interfere with thyroid hormone production.
- Environmental contaminants. Certain industrial chemicals, such as PCBs, found in the local environment at high levels may also cause hypothyroidism.
Hypothyroidism sometimes is referred to as a “silent” disease because early symptoms may be so mild that no one realizes anything is wrong. Untreated symptoms become more noticeable and severe, and can lead to confusion and mental disorders, breathing difficulties, heart problems, fluctuations in body temperature, and death.
Someone who has hypothyroidism will probably have more than one of the following symptoms:
- decreased heart rate
- progressive hearing loss
- weight gain
- problems with memory and concentration
- goiter (enlarged thyroid gland)
- muscle pain or weakness
- loss of interest in sex; decreased libido
- numb, tingling hands
- dry skin
- swollen eyelids
- dryness, loss, or premature graying of hair
- extreme sensitivity to cold
- irregular menstrual periods
- hoarse voice
Hypothyroidism usually develops gradually. When the disease results from surgery or other treatment for hyperthyroidism, symptoms may appear suddenly and include severe muscle cramps in the arms, legs, neck, shoulders, and back. It’s important to see a doctor if any of these symptoms appear unexpectedly.
When hypothyroidism remains undiagnosed and untreated, a person may eventually develop myxedema. Symptoms of this rare but potentially deadly complication include enlarged tongue, swollen facial features, hoarseness, and physical and mental sluggishness.
Myxedema coma is characterized by unresponsiveness, irregular and shallow breathing, and a drop in blood pressure and body temperature. The onset of this medical emergency can be sudden in people who are elderly or have been ill, injured, or exposed to very cold temperatures; who have recently had surgery; or who use sedatives or antidepressants. Without immediate medical attention, myxedema coma can be fatal.
The diagnosis of hypothyroidism is based on the patient’s observations, medical history, physical examination, and thyroid function tests. Doctors who specialize in treating thyroid disorders (endocrinologists) are most apt to recognize subtle symptoms and physical indications of hypothyroidism.
A blood test known as a thyroid-stimulating hormone (TSH) assay, tests of T4 and T3 levels, a thyroid nuclear medicine scan, and thyroid ultrasound are used to confirm the diagnosis.
A woman being tested for hypothyroidism should let her doctor know if she is pregnant or breastfeeding. All patients should be sure their doctors are aware of any recent procedures involving radioactive materials or contrast media.
The TSH assay is extremely accurate, but some doctors doubt the test’s ability to detect mild hypothyroidism. They advise patients to monitor their basal (resting) body temperature for below-normal readings that could indicate the presence of hypothyroidism.
These readings should be taken for five consecutive days, starting on the second day of the menstrual cycle for female patients. The normal temperature reading is 97.5°F (36.4°C).
Alternative treatments are aimed primarily at strengthening the thyroid gland and will not eliminate the need for thyroid hormone medications. They include nutritional therapy, herbal therapy, and exercise.
If a person is experiencing symptoms resembling those of hypothyroidism, it is best to talk to a family physician immediately for appropriate diagnosis and treatments. Nutritional therapy should only be complementary and not used to replace conventional treatment for this disorder.
In 2004, a study found that feeding soy formula to infants with congenital hypothyroidism led to prolonged increases in TSH levels. The study authors recommended close follow-up and frequent TSH measures if infants are put on soy-based formulas.
A naturopath or a nutritionist may recommend the following dietary changes to improve mild hypothyroidism:
- Avoiding eating the following raw foods: cabbage, mustard, spinach, cassava roots, peanuts, soybeans, and peaches. They may interfere with thyroid hormone production if not cooked.
- Eating foods with high iodine content such as fish, shellfish, and seaweed.
- Taking multivitamin and mineral supplements daily. Vitamins A, B2, B3, B6, E, and zinc are needed for normal thyroid hormone production.
- Strengthening thyroid function with thyroid preparations sold at local food stores. They are used to treat mild hypothyroidism only. Available products include thyroid extracts, iodine, zinc, or tyrosine. Most Americans may not need iodine supplements, as the daily requirement can easily be met by eating iodine-rich foods or using iodized salt. Consuming more than 600 mcg of iodine per day may result in toxicity.
Herbal remedies to improve thyroid function and relieve thyroid symptoms include Siberian ginseng (for treatment of fatigue), Panax ginseng, and bladder wrack (Fucus vesiculosus,) which can be taken in capsule form or as a tea.
Homeopathic treatments (tiny doses of diluted, safe remedies to promote healing) may gradually reduce the need for supplemental thyroid hormone in some patients. Homeopathic remedies for hypothyroidism include homeopathic thyroid as well as others based on the patient’s individualized symptoms.
Exercise improves thyroid function by stimulating production of thyroid hormone and making body tissues more responsive to the effects of thyroid hormone. It also increases the metabolic (chemical changes in cells providing energy to the body) rate and helps hypothyroid patients lose weight.
In allopathic treatment—medical practice that combats disease with remedies that produce effects different from those produced by the disease—natural or synthetic thyroid hormones are used to restore normal (euthyroid) thyroid hormone levels.
Synthroid, or synthetic T4, is easy to take and works for about 80% of patients. In addition, some patients need additional T3. However, physicians have not agreed for many years on adding this therapy. In 2004, a study showed there were no benefits to adding T3 to traditional T4 therapy.
Synthetic hormones are more effective than natural substances, but it may take several months to determine the correct dosage. Patients start to feel better within 48 hours, but symptoms will return if they stop taking the medication.
Most doctors prescribe levothyroxine sodium tablets, and most people with hypothyroidism will take the medication for the rest of their lives. Aging, other medications, and changes in weight and general health can affect how much replacement hormone a patient needs, and regular TSH tests are used to monitor hormone levels. Patients should not switch from one brand of thyroid hormone to another without a doctor’s permission.
Possible side effects of too much T4 or T3 include osteoporosis (after long-term use), occasional anxiety, heart palpitations (very fast, strong heartbeat), insomnia, and occasional episodes of mania (acting crazed).
Regular exercise and a high-fiber diet can help maintain thyroid function and prevent constipation.
Thyroid hormone replacement therapy generally maintains normal thyroid hormone levels unless treatment is interrupted or discontinued. In 2004, a study showed that treating hypothyroidism reduces risk of cardiac disease, particularly from atherosclerosis, or hardened arteries from plaque buildup.
Primary hypothyroidism can’t be prevented, but routine screening of adults can detect the disease in its early stages and prevent complications.