It is well known that breast cancer is the number one most-diagnosed cancer in women, but it is not as well known that millions of women are afflicted with thyroid disorders. Breast cancer can be highly reactive to hormones such as estrogen. Thyroid-generated hormones can have very estrogen-like effect when produced at high levels, which begs the question can an overabundance of thyroid hormones contribute to developing breast cancer? A study conducted in Denmark suggests that this could be the case… maybe.
Your thyroid is often referred to as being butterfly-shaped and can be found at the very base of your neck. It produces the many hormones, but the most important physiologically are triiodothyronine (T3) and its precursor, thyroxine (T4). These hormones are derived from the amino acid tyrosine and are primarily responsible for regulation of your metabolism. These hormones do an incredible amount of work in your body.
Thyroid hormones interact with almost every cell in the body. They increase the basal metabolic rate (the body’s ability to generate heat) and affect protein synthesis. They are essential to proper cell development and differentiation of all cells within the body. They regulate the metabolization of protein, fat, and carbohydrates, as well vitamins.
Individuals can develop hyperthyroidism, which is referred to as an “overactive” thyroid. In this situation, “too much” thyroid hormones are being produced. Symptoms included weight loss, hair loss, increased perspiration (sweat), increased anxiety, and heartbeat. Women are 5 to 10 times more likely than men to develop hyperthyroidism.
Hypothyroidism is an underactive thyroid — when not enough thyroid hormone is produced. Symptoms manifest as weight gain, constant fatigue, feeling listless, depression, slow moving bowels, constipation, and it is more commonly found in women.
To determine the effect of thyroid hormone on breast cancer risks, Danish scientists studied two large groups of women, all of who had thyroid disease over the time period of 1978 to 2013. They studied over 60,000 women who had an underactive thyroid (hypothyroidism) and over 80,000 women who had and overactive thyroid (hyperthyroidism). These women where followed for 5 to 7 years and it was discovered that women with hyperthyroidism had a slight increase in their risk for breast cancer. Women with hypothyroidism had a 6% decrease in breast cancer risk.
The study seems to point to excess thyroid hormone production being linked to breast cancer, but it requires more study. If there is an association, it is not definitive that hyperthyroidism causes the development of breast cancer. It is recommended that women who have hyperthyroidism be aware of the possible risk and have regular examinations for breast cancer.