Just a snippet from "you and your hormones" from the Society for Endocrinology.
(if, like me, you've been told weight gain is nothing to do with it!)
"Hypothyroidism in adults causes a decreased metabolic rate. This results in symptoms which include fatigue, intolerance of cold temperatures, low heart rate, weight gain, reduced appetite, poor memory, depression, stiffness of the muscles and infertility."
And Vitamin D IS a hormone....