TPO and thyroid gland disorder: Effects of smoking on thyroid disorders have caused major concern, some  studies demonstrated that smoking did not have any significant relationship with thyroid functions (4), while others reported that smoking is associated with a decreased level of anti‐thyroid peroxidase antibodies (anti‐TPO Ab) and thyroid‐stimulating hormone (TSH) levels (5-7).TSH and free thyroxine (F4) levels are important indicators used to diagnose thyroid disorders (8) and assessing thyroid function according to smoking status.