Breast Cancer Risk Increases With Presence of Overactive Thyroid in Women

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A new study from a team of Danish researchers suggests that the level of activity by the thyroid gland in women could have a direct relationship with breast cancer risk.

The findings of the research published in the February 2016 issue of the European Journal of Endocrinology showed that those women whose thyroid glands produce more thyroid hormones have an increased risk of breast cancer by 11 percent compared to those who have normal functioning thyroids. Those who produced fewer thyroid hormones have 6 percent less likelihood of developing the condition, WebMD wrote.

"High levels of thyroid hormone levels can have estrogen-like effects, which may explain why hyperthyroidism is associated with higher risk of breast cancer," said Dr. Mette Søgaard, who is involved in the study.

"Our findings emphasize the importance of raising awareness of breast cancer in women with hyperthyroidism, and further our understanding of this potential risk."

The study took into account medical records from over 4 million Danish women in a study period of 36 years. The researchers only included those who do not have cancer and were only diagnosed with thyroid disease for the first time. More than 80,000 women from the study were diagnosed with an overactive thyroid gland and around 61,800 with an underactive thyroid gland.

According to the WebMD, the thyroid is a gland found at the front portion of the neck and is shaped like a butterfly. The gland secretes various thyroid hormones like thyroxine. These hormones affect a person's metabolism, growth and development, and body temperature.

When the thyroid nodule becomes overactive and excessively produce thyroid hormones, hyperthyroidism occurs. On the other hand, when thyroid hormones are produced in low levels, hypothyroidism takes place and one of the most common cause is an autoimmune disease.

There are some limitations to the study, however, that could make other experts feel a bit skeptical on the correlation between an overactive thyroid and breast cancer risk, US News Health reported.

"First of all, this is a very homogenous group of women," Dr. Courtney Vito, a breast surgeon and an assistant clinical professor of surgical oncology at the City of Hope Comprehensive Cancer Center in Duarte, California, said regarding the participants of the study.

"There would never be a study group like that in the U.S., where there is a lot of ethnic variation and we are a much more heterogeneous population. So, these findings might not be generalizable across other populations," she said.

For Richard Berks, senior research officer at Breast Cancer Now, there is a need for further studies to corroborate the causal relationship. He said that the studies only show a slight link and there are other breast cancer risk factors in women that show more certainty.

He cited the lifestyle of a woman, alcohol consumption, level of physical activity and weight as some of the potential influencing risks.