Several years after the 1986 disaster at the Chernobyl nuclear power plant in Ukraine, the incidence of thyroid cancer rose among local children. Local authorities have recognized only thyroid cancer as being caused by the nuclear accident.
The butterfly-shaped thyroid gland is located just below the Adam’s apple and is attached to the trachea. The thyroid gland produces thyroid hormone by absorbing iodine, which is contained in foods such as kombu seaweed.
If a person breathes in or absorbs radioactive iodine through food and drink, 10 to 30 percent of this iodine is said to accumulate in the thyroid.
As a diagnostic tool and as a treatment for hyperthyroidism and thyroid cancer, radioactive iodine has helped countless people recover from thyroid diseases. Yet, despite its glowing role in modern medicine, exposure to this powerful substance can surreptitiously lead to thyroid cancer. Knowledge of this comes from studies of populations exposed to the isotope I-131 from the accident at the Chernobyl nuclear power plant in the Ukraine during the 1980s and from atomic bomb tests carried out in the United States during the 1950s and 1960s.
Exposure to radiation from nuclear fallout also increases the risk of thyroid cancer later in life if you were exposed during childhood. Studies conducted by the National Cancer Institute
have found increased thyroid cancer rates in populations affected by the accident at the Chernobyl nuclear reactor in Ukraine in 1986 and by atomic bomb testing in the United States during the 1940s, 1950s, and 1960s. If you believe you were exposed to either harmful X-rays or fallout, talk to your doctor about a thyroid evaluation. The level of radiation used in routine X-rays for dental exams or other diagnostic purposes is not high enough to have an effect on your thyroid gland.
The Chernobyl accident also made it clear that the risk for thyroid cancer decreases with increasing age at the time of exposure and that there is almost no risk to those who were over the age of forty when exposed. The accident also demonstrated that exposure to fallout increases the risk for benign thyroid diseases, including benign nodules and hypothyroidism. Among children, higher TSH levels were found in the geographic areas where there was the highest exposure to fallout; however, the total incidence of hypothyroidism that resulted from such exposure is unknown. Theoretically, hypothyroidism can result from receiving
radiation doses high enough to destroy part of the thyroid. Less often, fallout exposure is believed to induce autoimmune thyroid disease by sensitizing lymphocytes to thyroid cells. This can result in hypothyroidism and, very rarely, hyperthyroidism.
A risk factor is anything that affects a person’s chance of getting a disease such as cancer.
Different cancers have different risk factors. For example, smoking is a risk factor for cancers of the lung, mouth, larynx (voice box), bladder, kidney, and several other organs. But risk factors don’t tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get the disease. And many people who get the disease may not have had any known risk factors. Even if a person with thyroid cancer has a risk factor, it is very hard to know how much that risk factor may have contributed to the cancer.
Scientists have found a few risk factors that make a person more likely to develop thyroid cancer.
Gender and age
For unclear reasons thyroid cancers (like almost all diseases of the thyroid) occur about 3
times more often in women than in men. Thyroid cancer can occur at any age, but the risk peaks earlier for women (who are most often in their 40s or 50s when diagnosed) than for men (who are usually in their 60s or 70s).
A diet low in iodine
Follicular thyroid cancers are more common in areas of the world where people’s diets are low in iodine. In the United States, most people get enough iodine in their diet because it is added to table salt and other foods. A diet low in iodine may also increase the risk of papillary cancer if the person also is exposed to radioactivity.
Exposure to radiation is a proven risk factor for thyroid cancer. Sources of such radiation
include certain medical treatments and radiation fallout from power plant accidents or nuclear weapons. Having had head or neck radiation treatments in childhood is a risk factor for thyroid
cancer. Risk depends on how much radiation is given and the age of the child. In general, the risk increases with larger doses and with younger age at treatment. Before the 1960s, children were sometimes treated with low doses of radiation for things we wouldn’t use radiation for now, like acne, fungus infections of the scalp (ringworm), an enlarged thymus gland, or enlarged tonsils or adenoids. Years later, the people who had these treatments were found to have a higher risk of thyroid cancer. Radiation therapy in childhood for some cancers such as lymphoma, Wilms tumor, and neuroblastoma also increases risk. Thyroid cancers associated with prior radiation therapy are not more serious than other thyroid cancers.
Several studies have pointed to an increased risk of thyroid cancer in children because of radioactive fallout from nuclear weapons or power plant accidents. For instance, thyroid cancer is several times more common than normal in children living near Chernobyl, the site of a 1986 nuclear plant accident that exposed millions of people to radioactivity. Adults involved with the cleanup after the accident and those who lived near the plant have also had a higher rate of thyroid cancer. Children who had more iodine in their diet appeared to have a lower risk.
Some radioactive fallout occurred over certain regions of the United States after nuclear weapons were tested in western states during the 1950s. This exposure was much, much lower than that around Chernobyl. A higher risk of thyroid cancer has not been proven at these low exposure levels. If you are concerned about possible exposure to radioactive fallout, discuss this with your doctor.
Hereditary conditions and family history
Several inherited conditions have been linked to different types of thyroid cancer.