What is it and how does it affect me?

Thyroid-Stimulating Hormone, or TSH, is produced by the pituitary gland and regulates the production of thyroid hormones by the thyroid gland. TSH levels are affected by a number of factors, including stress, diet, and certain medications. An imbalance of TSH levels may indicate an underactive or overactive thyroid, which can cause fatigue and diminish your ability to effectively exercise.