“Hypothyroidism, also called underactive thyroid, is when the thyroid gland doesn’t make enough thyroid hormones to meet your body’s needs. Thyroid hormones control the way the body uses energy, so they affect nearly every organ in your body, even the way your heart beats. Without enough thyroid hormones, many of your body’s functions slow down.”

NIH National Institute of Diabetes and DIgestive and Kidney dieseases.