For many years doctors and researchers have noticed that women with hypothyroidism (an under active thyroid) are at increased risk for Breast Cancer.

Dr. James Howenstine, in his article Thyroid Hormone Therapy Appears To Cause Breast Cancer, notes that women taking thyroid hormone appear to be twice (12.1%) as likely to develop breast cancer as women not using thyroid hormone (6.2%).  Women who had taken thyroid hormone for 15 years had a 19.5% incidence of breast cancer whereas women who have only taken thyroid hormone for 5 years had only a 10% incidence of breast cancer.

Medical journalist Zosia Chustecka  in her article, Breast Cancer Patients May Have Subtle Thyroid Dysfunction, and Chris Woollams  in his article, Is synthetic thyroid hormone behind your cancer?, provide valuable insight and clinical outcomes to further support this link.