Hyperthyroidism, or overactive thyroid, happens when your thyroid gland makes more thyroid hormones than your body needs.

Your thyroid is a small, butterfly-shaped gland in the front of your neck. It makes hormones that control the way the body uses energy. These hormones affect nearly every organ in your body and control many of your body's most important functions. For example, they affect your breathing, heart rate, weight, digestion, and moods. If not treated, hyperthyroidism can cause serious problems with your heart, bones, muscles, menstrual cycle, and fertility. But there are treatments that can help.

Hyperthyroidism has several causes. They include:

• Graves' disease, an autoimmune disorder in which your immune system attacks your thyroid and causes it to make too much hormone. This is the most common cause.
• Thyroid nodules, which are growths on your thyroid. They are usually benign (not cancer). But they may become overactive and make too much thyroid hormone. Thyroid nodules are more common in older adults.
• Thyroiditis, inflammation of the thyroid. It causes stored thyroid hormone to leak out of your thyroid gland.
• Too much iodine. Iodine is found in some medicines, cough syrups, seaweed and seaweed-based supplements. Taking too much of them can cause your thyroid to make too much thyroid hormone.
• Too much thyroid medicine. This can happen if people who take thyroid hormone medicine for hypothyroidism (underactive thyroid) take too much of it.

You are at higher risk for hyperthyroidism if you:

• Are a woman
• Are older than age 60
• Have been pregnant or had a baby within the past 6 months
• Have had thyroid surgery or a thyroid problem, such as goiter
• Have a family history of thyroid disease
• Have pernicious anemia, in which the body cannot make enough healthy red blood cells because it does not have enough vitamin B12
• Have type 1 diabetes or primary adrenal insufficiency, a hormonal disorder
• Get too much iodine, from eating large amounts of foods containing iodine or using iodine-containing medicines or supplements

The symptoms of hyperthyroidism can vary from person to person and may include:

• Nervousness or irritability
• Fatigue
• Muscle weakness
• Trouble tolerating heat
• Trouble sleeping
• Tremor, usually in your hands
• Rapid and irregular heartbeat
• Frequent bowel movements or diarrhea
• Weight loss
• Mood swings
• Goiter, an enlarged thyroid that may cause your neck to look swollen. Sometimes it can cause trouble with breathing or swallowing.

Adults over age 60 may have different symptoms than younger adults. For example, they may lose their appetite or withdraw from other people. Sometimes this can be mistaken for depression or dementia.

If hyperthyroidism isn't treated, it can cause some serious health problems, including:

• An irregular heartbeat that can lead to blood clots, stroke, heart failure, and other heart problems
• An eye disease called Graves' ophthalmopathy. It can cause double vision, light sensitivity, and eye pain. In rare cases, it can lead to vision loss.
• Thinning bones and osteoporosis
• Fertility problems in women
• Complications in pregnancy, such as premature birth, low birth weight, high blood pressure in pregnancy, and miscarriage

Your health care provider may use many tools to make a diagnosis:

• A medical history, including asking about symptoms
• A physical exam
• Thyroid tests, such as
  • TSH, T3, T4, and thyroid antibody blood tests
  • Imaging tests, such as a thyroid scan, ultrasound, or radioactive iodine uptake test. A radioactive iodine uptake test measures how much radioactive iodine your thyroid takes up from your blood after you swallow a small amount of it.

The treatments for hyperthyroidism include medicines, radioiodine therapy, and thyroid surgery:

• Medicines for hyperthyroidism include
  • Antithyroid medicines, which cause your thyroid to make less thyroid hormone. You probably need to take the medicines for 1 to 2 years. In some cases, you might need to take the medicines for several years. This is the simplest treatment, but it is often not a permanent cure.
  • Beta blocker medicines, which can reduce symptoms such as tremors, rapid heartbeat, and nervousness. They work quickly and can help you feel better until other treatments take effect.
• Radioiodine therapy is a common and effective treatment for hyperthyroidism. It involves taking radioactive iodine by mouth as a capsule or liquid. This slowly destroys the cells of the thyroid gland that produce thyroid hormone. It does not affect other body tissues. Almost everyone who has radioactive iodine treatment later develops hypothyroidism. This is because the thyroid hormone-producing cells have been destroyed. But hypothyroidism is easier to treat and causes fewer long-term health problems than hyperthyroidism.
• Surgery to remove part or most of the thyroid gland is done in rare cases. It might be an option for people with large goiters or pregnant women who cannot take antithyroid medicines. If you have all of your thyroid removed, you will need to take thyroid medicines for the rest of your life. Some people who have part of their thyroid removed also need to take medicines.

If you have hyperthyroidism, it's important not to get too much iodine. Talk to your health care provider about which foods, supplements, and medicines you need to avoid.

NIH: National Institute of Diabetes and Digestive and Kidney Diseases

Your immune system is a complex network of cells, tissues, and organs. Together they help the body fight infections and other diseases.

When germs such as bacteria or viruses invade your body, they attack and multiply. This is called an infection. The infection causes the disease that makes you sick. Your immune system protects you from the disease by fighting off the germs.

The immune system has many different parts, including:

• Your skin, which can help prevent germs from getting into the body
• Mucous membranes, which are the moist, inner linings of some organs and body cavities. They make mucus and other substances which can trap and fight germs.
• White blood cells, which fight germs
• Organs and tissues of the lymph system, such as the thymus, spleen, tonsils, lymph nodes, lymph vessels, and bone marrow. They produce, store, and carry white blood cells.

Your immune system defends your body against substances it sees as harmful or foreign. These substances are called antigens. They may be germs such as bacteria and viruses. They might be chemicals or toxins. They could also be cells that are damaged from things like cancer or sunburn.

When your immune system recognizes an antigen, it attacks it. This is called an immune response. Part of this response is to make antibodies. Antibodies are proteins that work to attack, weaken, and destroy antigens. Your body also makes other cells to fight the antigen.

Afterwards, your immune system remembers the antigen. If it sees the antigen again, it can recognize it. It will quickly send out the right antibodies, so in most cases, you don't get sick. This protection against a certain disease is called immunity.

There are three different types of immunity:

• Innate immunity is the protection that you are born with. It is your body's first line of defense. It includes barriers such as the skin and mucous membranes. They keep harmful substances from entering the body. It also includes some cells and chemicals which can attack foreign substances.
• Active immunity, also called adaptive immunity, develops when you are infected with or vaccinated against a foreign substance. Active immunity is usually long-lasting. For many diseases, it can last your entire life.
• Passive immunity happens when you receive antibodies to a disease instead of making them through your own immune system. For example, newborn babies have antibodies from their mothers. People can also get passive immunity through blood products that contain antibodies. This kind of immunity gives you protection right away. But it only lasts a few weeks or months.

Sometimes a person may have an immune response even though there is no real threat. This can lead to problems such as allergies, asthma, and autoimmune diseases. If you have an autoimmune disease, your immune system attacks healthy cells in your body by mistake.

Other immune system problems happen when your immune system does not work correctly. These problems include immunodeficiency diseases. If you have an immunodeficiency disease, you get sick more often. Your infections may last longer and can be more serious and harder to treat. They are often genetic disorders.

There are other diseases that can affect your immune system. For example, HIV is a virus that harms your immune system by destroying your white blood cells. If HIV is not treated, it can lead to AIDS (acquired immunodeficiency syndrome). People with AIDS have badly damaged immune systems. They get an increasing number of severe illnesses.

We usually think of air pollution as being outdoors, but the air in your house or office could also be polluted. Sources of indoor pollution include:

• Mold and pollen
• Tobacco smoke
• Household products and pesticides
• Gases such as radon and carbon monoxide
• Materials used in the building such as asbestos, formaldehyde and lead

Sometimes a group of people have symptoms that seem to be linked to time spent in a certain building. There may be a specific cause, such as Legionnaire's disease. Sometimes the cause of the illness cannot be found. This is known as sick building syndrome.

Usually indoor air quality problems only cause discomfort. Most people feel better as soon as they remove the source of the pollution. However, some pollutants can cause diseases that show up much later, such as respiratory diseases or cancer.

Making sure that your building is well-ventilated and getting rid of pollutants can improve the quality of your indoor air.

Environmental Protection Agency

Infertility means not being able to become pregnant after a year of trying. If a woman can get pregnant but keeps having miscarriages or stillbirths, that's also called infertility.

Infertility is fairly common. After one year of having unprotected sex, about 15% of couples are unable to get pregnant. About a third of the time, infertility can be traced to the woman. In another third of cases, it is because of the man. The rest of the time, it is because of both partners or no cause can be found.

There are treatments that are specifically for men or for women. Some involve both partners. Drugs, assisted reproductive technology, and surgery are common treatments. Happily, many couples treated for infertility go on to have babies.

NIH: National Institute of Child Health and Human Development

Iron is a mineral that our bodies need for growth and development. Your body uses iron to make hemoglobin, a protein in red blood cells. Hemoglobin carries oxygen from the lungs to all parts of the body. Iron is also important for healthy muscles, bone marrow, and organ function. Your body also needs iron to make some hormones.

Iron is found naturally in many foods and is added to some fortified food products. Foods that are high in iron include:

• Lean meat, seafood, and poultry
• Iron-fortified breakfast cereals and breads
• White beans, lentils, spinach, kidney beans, and peas
• Nuts and some dried fruits, such as raisins

Iron is available in supplements, either on its own or as part of many multivitamin/mineral supplements.

Most people in the United States get enough iron. The amount that you need each day depends on your age, your sex, and whether you consume a mostly plant-based diet.

Sometimes people can have trouble getting enough iron. There can be many causes, including blood loss, a poor diet, or a problem absorbing enough iron from foods. Those who are more likely to have low iron include people who:

• Have heavy periods
• Are pregnant or breastfeeding
• Are infants (especially if they were born premature or low birth weight)
• Are frequent blood donors
• Have cancer, certain digestive diseases, or heart failure
• Are on kidney dialysis
• Have trouble absorbing iron because they:
  • Have a digestive condition such as celiac disease, ulcerative colitis, Crohn's disease, or Helicobacter pylori infection
  • Had weight loss surgery

If you have too little iron, you may develop iron-deficiency anemia. It may not cause symptoms at first, but over time, it can cause fatigue, shortness of breath, and trouble with memory and concentration. Treatment for low iron and iron-deficiency anemia is usually with iron supplements.

Too much iron can damage your body. For example, if you are healthy and take too many iron supplements, you may have symptoms such as constipation, nausea and vomiting, abdominal (belly) pain, and diarrhea. Higher iron levels can cause ulcers. Extremely high levels can lead to organ damage, coma, and death.

A disease called hemochromatosis can cause too much iron to build up in the body. Hemochromatosis is inherited (passed down through families). It is usually treated by removing blood (and iron) from your body on a regular basis.

National Institutes of Health, Office of Dietary Supplements