Dental X-rays May Increase Risk of Thyroid Cancer


Does exposure to dental x-rays raise a person’s risk of developing thyroid cancer? Since ionizing radiation is an established cause of thyroid cancer, researchers in England and Kuwait set out to examine a potential relationship between dental x-rays and this form of cancer.

Rise in thyroid cancer may be linked to x-ray exposure

Previous studies have shown an increased risk of thyroid cancer among dentists, dental assistants, and x-ray employees, and exposure to dental x-rays have also been associated with an increased risk of tumors of the salivary glands. Among the general population, since 1975 the incidence rates of thyroid cancer have doubled from 1.4 per 100,000 to 2.9 per 100,000 in 2006 in the United Kingdom.

The thyroid gland is a two-inch structure located in the front of the neck, below the voice box (larynx), and is responsible for the body’s metabolism and calcium balance. When dentists perform dental x-rays, the neck of the patient is exposed to radiation, placing the thyroid in the path of the harmful rays. The potential risk of cancer is especially important because children and adolescents often are subjected to x-rays for dental problems.

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The estimated new cases of thyroid cancer in the United States in 2010 is 44,670, according to the National Cancer Institute, and 1,690 people are estimated to die of the disease. About one in 111 men and women can expect to develop thyroid cancer during their lifetime, and women are about three times more likely to have the disease.

A research team composed of scientists from Brighton and Cambridge in England and from Kuwait evaluated 313 patients in Kuwait, all of whom had thyroid cancer. They were compared with a similar number of matched controls. Because dental treatment is free in Kuwait, individuals are more likely to have dental x-rays. The incidence of thyroid cancer also happens to be high in Kuwait.

Analysis revealed that exposure to dental x-rays was significantly associated with an increased risk of thyroid cancer and was related to dose. The researchers point out, however, that because this was a self-reported study without access to dental x-ray records, further investigation is needed to support this finding.

Dr. Anjum Memon, senior lecturer and consultant in public health medicine at Brighton and Sussex Medical School, noted that “The public health and clinical implications of these findings are particularly relevant in the light of increases in the incidence of thyroid cancer in many countries over the past 30 years.” He also pointed out that “the notion that low-dose radiation exposure through dental radiography is absolutely safe needs to be investigated further” and that dental x-rays “should be prescribed when the patient has a specific clinical need, and not as part of routine check-up.”

Memom A et al. Acta Oncologica 2010 May; 49(4): 447-53
National Cancer Institute