Long-term hypothyroidism in women significantly increases the risk of developing hepatocellular carcinoma (liver cancer), according to the results of a study published in Hepatology.
The liver is the largest organ in the body and is responsible for over 500 functions, including the secretion of glucose, proteins, vitamins, and fats; the production of bile; the processing of hemoglobin; and detoxification of numerous substances. Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer (cancer that begins in the liver). Factors that increase the risk of developing HCC include long-term, heavy alcohol use and chronic infection with hepatitis B or C viruses.
Hepatocellular carcinoma is the third leading cause of cancer deaths worldwide, and the disease appears to be on the rise, possibly due to an increased incidence of the hepatitis B and C viruses.
The thyroid releases hormones that control the metabolism. Hypothyroidism is a condition in which the thyroid gland fails to produce enough thyroid hormone. Hypothyroidism is more common in women than men and also in individuals over age 50 or those who have been exposed to radiation.
There is some evidence of a link between thyroid disease and hepatitis C virus. In addition, there is evidence that hypothyroidism is related to inflammation of the liver cells. However, no clear link has been established between hypothyroidism and liver cancer.
Researchers at M. D. Anderson Cancer Center in Texas conducted a study to compare the incidence of HCC among patients with and without hypothyroidism. The study included 420 patients with HCC and 1,104 healthy control subjects. The researchers found that a long-term history of hypothyroidism (10 or more years) was associated with a statistically significant high risk of HCC in women —specifically, they were 2.9 times more likely to develop HCC than women without thyroid disease.
Hypothyroidism did not appear to increase the risk of HCC for men. Hyperthyroidism (overactive thyroid) did not increase the risk of HCC in either sex.
The researchers concluded that women with long-term hypothyroidism are at an increased risk of developing HCC. It is unclear whether the weight gain often associated with hypothyroidism plays a role in the development of HCC, as hypothyroidism that did not result in weight gain also appeared to contribute to the development of HCC. Research will likely be ongoing to continue to evaluate this link.
 Hassan MM, Kaseb A, Li D, et al. Association between hypothyroidism and hepatocellular carcinoma: A case-control study in the United States. Hepatology. 2009; 49: 1563-1570.