Understanding your thyroid
What is metabolism?
Metabolism is the chemical activity by which cells convert nutrients into energy. Thyroid hormone sets the pace of metabolism. During metabolism, energy is released from carbohydrates, proteins, fats, and other nutrients you eat. The metabolic process also generates heat, carbon dioxide, water, and waste products. Your cells use the energy to carry out essential chemical transformations that empower your body tissues to function properly. Metabolism affects body temperature, body weight, energy level, muscle strength, psychological health, fertility, and more.
Figure 1: How common is thyroid disease?
Nearly 6% of the U.S. population has thyroid disease. Most of these people have hypothyroidism. A much smaller portion of people have hyperthyroidism.
Source: Third U.S. National Health and Nutrition Examination Survey (NHANES III).
How the thyroid gland works
Just as your car engine can’t run without gasoline, your thyroid needs fuel to produce thyroid hormone. This fuel is iodine. Iodine is found in such foods as iodized table salt, seafood, bread, and milk. When you eat these foods, the iodine passes into your bloodstream. Your thyroid then extracts this necessary ingredient from your blood and uses it to make two kinds of thyroid hormone: thyroxine, called T4 because it contains four iodine atoms, and triiodothyronine, or T3, which contains three iodine atoms. The thyroid’s output consists primarily of T4 (see Figure 2). Most of the T3 the body needs is actually created outside the thyroid in organs and tissues that use T3, such as the liver, kidneys, and brain. These tissues convert T4 from the thyroid into T3 by removing an iodine atom.
Figure 2: Normal thyroid
Normally, the hypothalamus sends a signal in the form of thyrotropin-releasing hormone (TRH) that enables the pituitary gland to secrete thyroid-stimulating hormone (TSH). In response, the thyroid gland releases T4 and a small amount of T3. These travel to the liver and other organs, where T4 is converted to T3 and enters the bloodstream. Like a heating system with a thermostat set at a constant temperature, a normally functioning thyroid operates at a steady pace without much variation.
As the thyroid produces thyroid hormone, it stores it in a vast number of microscopic follicles shaped like spheres. When the body needs thyroid hormone, the thyroid secretes it into your bloodstream in quantities suitable to meet the metabolic needs of your cells. The hormone easily slips into cells in need and attaches to special receptors located in the cells’ nuclei.
Your car engine burns fuel, but it is you who tells it how hard to work by stepping on the gas pedal. The thyroid also needs to be told what to do. It takes its orders from your pituitary gland, located at the base of your brain. No larger than a pea, the pituitary is sometimes known as the “master” gland, because it controls functions of the thyroid and other glands in the endocrine system. The pituitary gland sends messages to your thyroid gland, telling it how much hormone to make. The messages come in the form of thyroid-stimulating hormone (TSH). TSH levels in your bloodstream rise or fall depending on whether there is enough thyroid hormone in your system to meet your body’s needs. Higher levels of TSH prompt the thyroid to produce more hormone, until TSH levels come down to a constant level. Conversely, low TSH levels signal the thyroid to slow down production.
The pituitary gland gets its information in several ways. It is able to read and respond directly to amounts of T4 circulating in the blood, but it also responds to the hypothalamus, a section of the brain that releases its own hormone, thyrotropin-releasing hormone (TRH). TRH stimulates TSH production in the pituitary gland. This network of communication between the hypothalamus, pituitary, and thyroid glands is referred to as the hypothalamic-pituitary-thyroid (HPT) axis.
When things go wrong
This network of communication is highly efficient. Normally, the thyroid doles out just the right amount of hormone to keep your body running smoothly. TSH levels remain fairly constant, yet they respond to the slightest changes in T4 levels, and vice versa.
But even the best network is subject to interference. Outside influences—such as disease or certain medicines—can break down communication. When this happens, the thyroid might not produce enough hormone, slowing down all of your body’s functions, a condition known as hypothyroidism or underactive thyroid. Or your thyroid could produce too much hormone, sending your systems into overdrive, a condition known as hyperthyroidism, or overactive thyroid.
When considering thyroid disease, doctors begin by asking two questions: First, is the thyroid gland producing an abnormal amount of thyroid hormone? And second, is there a structural change in the thyroid, such as a lump (nodule) or an enlargement (goiter)? Although one of these characteristics does not necessarily imply that the other is present, many thyroid disorders have both (see Table 1).
|Table 1: Thyroid disorders at a glance|
|Hashimoto’s thyroiditis||Sometimes||No, but may be difficult to distinguish from nodular thyroid disease||Yes||No||Most common cause of hypothyroidism in the United States.|
|Graves’ disease||Usually||No||No||Yes||Most common cause of hyperthyroidism in the United States.|
|Resolving thyroiditis (silent, postpartum, subacute)||Often||No||Yes||Yes||Thyroid leaks excessive hormone, causing thyrotoxicosis followed by a period of hypothyroidism before resolving on its own.|
|Iodine deficiency||Yes||May develop over a long period of time||Yes||No||Leading cause of hypothyroidism worldwide, but uncommon in non-immigrant U.S. population.|
|Solitary toxic adenoma||Yes||Yes||No||No||The goiter (enlargement) is due to the adenoma, a benign tumor.|
|Simple goiter||Yes||No||No||No||Thyroid enlargement with no known cause; thyroid function is normal.|
|Multinodular goiter||Yes||Yes||No||No||Can evolve into a toxic nodular goiter.|
|Toxic nodular goiter||Yes||Yes||No||No||Frequent cause of hyperthyroidism in older people.|
Sometimes the thyroid can’t meet the body’s demands for thyroid hormone, even when TSH levels increase. Your body slows down. You might feel cold, tired, and even depressed. You could gain weight, even though you’re eating less. This problem occurs for any of several reasons.
If you’re not getting enough iodine, your thyroid can’t make enough hormone but it will try to respond to rising TSH levels by working harder and harder anyway. This can cause a variety of symptoms. In some cases, the thyroid gland becomes enlarged and develops into a goiter, which looks like a protrusion or large swelling on your neck. At one time, immense goiters due to iodine deficiency were common, but today they are rare in developed countries because of the prevalence of iodine-fortified foods and foods enriched with iodized salt.
When a diseased thyroid enlarges, it’s known as goiter.
In other cases, the thyroid comes under attack by the body’s own immune system. Normally, substances called antibodies protect the body from dangerous bacteria and viruses. But in this condition, called Hashimoto’s thyroiditis, antibodies mistake the thyroid for a foreign invader. These antibodies, antithyroid peroxidase (anti-TPO) and antithyroglobulin (anti-Tg), are a hallmark of the destruction of the thyroid by the immune system. Over time, the defenseless thyroid, inflamed and scarred, surrenders and fails. Ailments like Hashimoto’s thyroiditis that result from an abnormal immune response are called autoimmune diseases. Hashimoto’s thyroiditis is also known as chronic lymphocytic thyroiditis; it is just one form of thyroiditis (inflammation of the thyroid), which causes hypothyroidism.
Fast fact: Thyroiditis
Thyroiditis is a term for any condition that causes thyroid inflammation and sometimes malfunction. Hashimoto’ s thyroiditis, the most common form of hypothyroidism in the United States, is caused by abnormal antibodies. Other forms of thyroiditis are usually temporary and cause the thyroid to leak hormone before crashing into a state of hypothyroidism.
Sometimes the thyroid keeps churning out thyroid hormone even when the pituitary gland completely shuts down TSH production, a clear signal that your body has had enough. Yet the thyroid appears oblivious to this signal and continues to produce too much, pushing metabolism into overdrive and speeding up your body’s processes. This is hyperthyroidism. If you’re hyperthyroid, your pulse may race and you might feel anxious, nervous, or irritable. You might become overheated, have trouble sleeping, and lose weight in spite of a good appetite. As with hypothyroidism, you may develop a goiter. In this case, because your thyroid is working so hard overproducing thyroid hormone, it enlarges.
The most common cause of a revved-up thyroid in the United States is an autoimmune disease called Graves’ disease. Antibodies attack the thyroid, stimulating the gland to overproduce thyroid hormone. The kinds of antibodies present in Graves’ disease are called TSH receptor antibodies (TRAb), including one kind known as thyroid-stimulating immunoglobulin (TSI). These work by mimicking TSH, attaching to the TSH receptor on the thyroid gland and confusing the thyroid so that it produces too much hormone. In addition to symptoms of hyperthyroidism, some people with Graves’ disease develop Graves’ eye disease, also known as thyroid eye disease. Its features vary from case to case but often include swollen or bulging eyes, redness, widely open eyelids, and double vision. In its most severe form, vision might diminish.
A toxic nodular goiter is to blame for hyperthyroidism in many people over age 60. This occurs when the thyroid enlarges and develops nodules, which are essentially lumps of thyroid cells that form as part of the thyroid. Nodules can develop on the outer surface of the gland, where the doctor can feel them during an examination. But if they develop inside the gland, they may not be apparent to the touch. Some nodules throw off communication between the thyroid and the pituitary gland because they independently produce thyroid hormone and do not depend on TSH for instructions.
In some cases, a type of single nodule, called a solitary toxic adenoma, causes hyperthyroidism in the same way, by producing thyroid hormone at its own whim, regardless of messages from the pituitary gland.
But not all nodules cause a thyroid hormone imbalance. There are different kinds of single nodules that can range from the size of a pea, or even smaller, to the size of a plum or larger. Most are completely harmless and don’t affect thyroid function in the least. These include fluid-containing nodules called cysts as well as adenomas, which are solid but equally harmless. A very small percentage of nodules are cancerous. Cancerous nodules do not directly affect thyroid function, and therefore do not cause an overactive or underactive thyroid.
Racing and burning out
A third category of thyroid disease, sometimes called resolving thyroiditis, includes conditions that cause your body to rev up and then slow down. In these conditions, an inflamed thyroid leaks too much thyroid hormone into the bloodstream, causing you to initially develop symptoms of hyperthyroidism. However, in this case your thyroid is leaking, not overproducing. This phase of resolving thyroiditis is referred to as the thyrotoxic phase, or thyrotoxicosis. Once your thyroid’s supply of the hormone is depleted, hormone levels fall below normal, and you then become hypothyroid. Eventually, in most people, the thyroid recovers on its own in about six to eight months, and normal function returns. However, with each episode, up to 25% of those affected develop permanent hypothyroidism.
These temporary forms of thyroiditis often occur in people with a family history of autoimmune disease. They sometimes go undetected because the inflammation is mild and painless. This is the case with postpartum thyroiditis, the most common form of resolving thyroiditis, which occurs in 4% to 9% of new mothers during the months following delivery of a baby. During this period, the immune system goes from being partially suppressed (as a result of hormonal changes in pregnancy) to being active, a transition that can trigger the disease. Silent thyroiditis is essentially the same as postpartum thyroiditis. The only difference is that it is unrelated to pregnancy and can occur in men or women, although it most often affects women.
Subacute thyroiditis is a painful version of the above-mentioned conditions that is sometimes caused by one of several viruses. Also known as de Quervain’s thyroiditis, subacute viral thyroiditis ranges in severity. If you have this disease and it’s on the severe side, you may feel like you’re suffering from the flu. You’ll have a fever, muscle aches and pains, and a painful, swollen thyroid gland that feels like a terrible sore throat. You might also experience detectable signs of too much thyroid hormone.
If you suspect you have thyroid disease, or any disease for that matter, it’s important to educate yourself to take full advantage of the doctor-patient relationship. Keep the following suggestions in mind as you seek help from your doctor.
Your primary care doctor
Two of the most common complaints that primary care doctors hear are “I’m always tired” and “I’m depressed.” This is not much to go on, considering that fatigue can indicate a variety of medical problems, or that your life is busy, you’ve been under a lot of stress, or you’re not getting enough sleep. Before you go to the doctor’s office, take a good look at what’s going on in your life and note anything that strikes you as unusual, as minor as it seems. Remember, with thyroid disease, even symptoms that may sound insignificant, such as “I’m always thirsty” or “I feel cold all the time” may suggest a thyroid problem.
Here are some other tips to foster a good doctor-patient partnership:
- Be thorough about your family’s medical history. Even if you think you know it, there may be some family members whose health you’re unsure of. It may be helpful to make a family tree listing all the conditions family members have had and bring it to your doctor.
- Before your visit, prepare a list of questions or write down symptoms you may forget to mention.
- If you are diagnosed with thyroid disease, become informed. Ask your doctor for literature on your condition. Then be sure to write down any questions you have. Also write down important information your doctor gives you or request written instructions to take with you.
Finding a specialist
Depending on your condition, you may see several different kinds of specialists over the course of treatment. But initially, you may be referred to either an endocrinologist or a thyroidologist. A thyroidologist specializes in thyroid disease, but not all endocrinologists do. Many treat mostly people who have diabetes.
So it may be wise to do a bit of your own homework to find a doctor who specializes in thyroid disease or who sees a significant number of thyroid patients. Once you have some names, call the offices to verify that the doctor accepts your health insurance and to set up consultations. If the doctor is an endocrinologist, find out how many thyroid patients the doctor sees each year versus the number of diabetes patients. If thyroid patients are few, you may want to go elsewhere. Once you’ve settled on a doctor, make sure to find out if your health plan requires a referral from your primary care physician.
When you visit the specialist, be sure that you fully understand any tests and procedures that he or she recommends for you. Request literature on the procedures and write down any questions or concerns that you have about them. The more you know, the more active a participant you can be in deciding which therapy is right for you. If, after your questions are answered, you are not convinced that the treatment your doctor recommends is right for you, you can seek a second opinion.
Finding a surgeon
If you are having a thyroidectomy, selecting a highly qualified surgeon is without a doubt the most important choice you’ll make. Your risk for complications, including damage to your parathyroid glands or laryngeal nerve, depends on the competency and experience of your surgeon. This may seem to be a daunting task, but it actually is not that difficult. If you use the guidelines below, you can significantly improve your chances of avoiding problems.
Choose an experienced surgeon who specializes in endocrine surgery. Make sure you pick a surgeon who performs thyroid operations frequently. This could be either a general surgeon who specializes in endocrine surgery, or a head and neck surgeon—also known as an otolaryngologist or ear, nose, and throat (ENT) surgeon—who has special expertise in endocrine surgery. For a child undergoing thyroidectomy, look for an endocrine surgeon, a pediatric surgeon, or an ENT surgeon with experience in the surgical management of childhood thyroid conditions.
Start with several recommendations. Your endocrinologist will probably recommend someone who meets the criteria outlined in this section. Ask for more than one name. You could also check with the professional organizations listed in the “Resources” section at the end of this report. Each of these groups has a website that enables you to search for physicians in your area. Once you have a few names, you can call and get some basic information about the doctor over the phone, including some of the information listed below. For any information you cannot get over the phone, make a note to ask those questions at your first appointment.
Find out if the surgeon is board-certified. This means that the surgeon has passed rigorous examinations prepared by leaders in that field of expertise. General surgeons are certified by the American Board of Surgery. Otolaryngologists are certified by the American Board of Otolaryngology.
Find out how many thyroid operations the surgeon performs each year. Be sure that the surgeon performs more than 30 thyroid or parathyroid operations each year.
Find out what the surgeon’s complication rate is. Your surgeon’s complication rate should be less than 2%. To determine the rate, you’ll need to ask the surgeon how many procedures he or she has performed in total and how many complications have resulted. If the surgeon doesn’t give a full and candid answer, find another surgeon.
Discuss the surgical procedure. You’ll want to be sure to talk specifically about the surgical procedure, what it involves, its risks, why it is recommended for you, and what your alternatives are.
Ask any questions you might have. It’s a good idea to write these down in advance of your appointment. Your surgeon should be willing to answer all of your questions.
If you choose a general surgeon, ask if he or she is a member of the American Association of Endocrine Surgeons. A general surgeon must perform a substantial number of thyroid operations each year with excellent outcomes to become a member of this professional organization. If the general surgeon is not a member, be certain he or she meets the rest of the criteria outlined in this section. If you are concerned about the surgeon’s experience or credentials, if you are not satisfied with the treatment plan, or if the surgeon seems unwilling to answer your questions, seek a second opinion.
Your endocrinologist or thyroidologist may recommend that you see one or more of the following specialists:
Cardiologist. If your thyroid disease is causing any problems with your heart, such as abnormal heart rhythms, you may be referred to a cardiologist, who specializes in treating people with heart problems. A cardiologist may be very involved in your treatment if you are being treated for hyperthyroidism and have an existing heart condition or are at risk for heart disease.
Ophthalmologist. An ophthalmologist specializes in eyes. You may be referred to one if you have eye problems associated with Graves’ disease.
Nuclear medicine specialist. If you are being tested with radioactive iodine, you are likely to encounter a doctor who specializes in nuclear medicine. This specialist typically interprets the radioactive iodine uptake test or radioactive thyroid scan. If you are being treated with radioactive iodine, your endocrinologist usually administers treatment, although sometimes a nuclear medicine doctor will handle treatment.
Living well with thyroid disease
The most important thing to know about living with thyroid disease is that you will probably need to take thyroid hormone replacement for the rest of your life. Whether you spontaneously developed hypothyroidism or you were treated for hyperthyroidism and became hypothyroid, you’ll need to stay on a regimen of daily medication and regular thyroid tests. The good news is that once medication puts your thyroid hormone levels within normal ranges, you are, in a sense, cured and can go on with your normal life, as long as you continue your medication. You’ll also need to avoid any substances—including drugs, supplements, and nutraceuticals—that can decrease its effectiveness. There are a few other measures you must keep in mind to ensure your optimal health.
When you first begin thyroid hormone medication, you need to have your levels of thyroid hormone checked every month or so, until the doctor is satisfied that you are getting the precise dosage of hormone your body requires. Once your symptoms improve, schedule a visit with your doctor every six to 12 months—your requirements for thyroid hormone might change over time. This is also true if you have a mild thyroid condition that does not require medication or if you are one of the few people who have been successfully treated for overactive thyroid without becoming hypothyroid. Some people in this group do eventually become hypothyroid many years down the road, so it is important to schedule check-ups at least once a year.
When you’re feeling good and leading a busy life, it’s easy to put these check-ups low on your list of concerns. But keep in mind that a number of factors can affect your thyroid hormone levels: illness, increasing age, changes in your diet, or pregnancy. You may need an adjustment in medication periodically.
So long as you continue medication to regulate your hormones, you can live a normal, active life.
Nutrition and exercise
There is no special diet you must follow while on thyroid hormone medication, with a couple of exceptions. Avoid foods high in soy protein, which can interfere with the absorption of thyroid hormone. If your thyroid was not removed or destroyed and you still have a substantial portion of your thyroid, avoid excessive amounts of iodine, either in medications or supplements, as this could trigger more problems with your thyroid. Most iodine-rich foods, such as iodized products or fish, are acceptable, but kelp and other thyroid supplements should be avoided. Aside from these restrictions, you are free to eat whatever you want, but as always, a healthy diet that includes lots of fruits, vegetables, and whole grains is an important part of healthy living.
Adopting a nutritious diet not only contributes to the renewed good feeling you experience once your thyroid levels are normal, but it helps your digestive system function smoothly and your heart pump efficiently—both of which support a healthy metabolism. If you still aren’t feeling good despite your medication, improving your diet and beginning an exercise program may help. Following are some tips for healthy living.
Eat nutritious foods. Soft drinks, potato chips, candy, crackers, and other junk foods that are high in calories and low in nutrition have become a mainstay of the American diet. If you normally eat a lot of these foods, minimizing them or cutting them out altogether and replacing them with a variety of fruits, vegetables, and whole-grain foods could make a difference in your overall health.
Cut down on “bad” fats. Certain dietary fats contribute to heart disease and some forms of cancer. The Food and Nutrition Board of the National Academy of Sciences has recommended a range of 20% to 35% of daily calories from fat of all kinds, reducing saturated fats and trans fats to a minimum. Saturated fats, which come mainly from animal products such as meat and cheese, and trans fats, which take the form of hydrogenated oils in manufactured food products and many margarines, should both be minimized because they raise levels of LDL cholesterol. LDL cholesterol, also known as “bad” cholesterol, can build up in the inner walls of your arteries and form plaque that can clog these arteries.
Many processed foods and snacks contain trans fats, so you may be consuming them without realizing it. Instead, choose fats that help reduce LDL cholesterol. These include monounsaturated and polyunsaturated fats from vegetable oils, and omega-3 fats, found in certain kinds of fish. Seeds, nuts, and legumes are also healthy choices.
Carbohydrates should fall in the range of 45% to 65% of your daily calories. Stick with complex carbohydrates found in whole-grain foods, fruits, and vegetables, and avoid heavy reliance on white starches and sugars. Protein should make up about 10% to 35% of your diet. Most people in developed countries get plenty of protein in their diets.
Limit dietary cholesterol. The American Heart Association recommends limiting dietary cholesterol to no more than 300 mg a day. If your cholesterol levels are high, try to consume no more than 200 mg per day. Sources high in cholesterol include animal fat, eggs, and full-fat dairy products.
Increase dietary fiber. Dietary fiber helps improve digestion. Eating whole-grain foods and a variety of vegetables and fruits helps ensure that you have an ample supply of dietary fiber. The Food and Nutrition Board recommends men ages 50 and younger get 38 grams daily; men over 50, 30 grams daily; women ages 50 and younger, 25 grams; and women over 50, 21 grams.
Exercise. People who exercise tend to live longer because exercise increases the heart’s pumping ability and the body’s oxygen use. These changes, in turn, provide extra energy and stamina. Exercise also burns calories and can help keep your weight down. Just walking 30 minutes a day on most days can help prevent heart disease and stroke and promotes general good health.