Optimal levels of iodine are critical for both healthy thyroid and breast tissue function.
One of the main problems caused by iodine deficiency is hypothyroidism, which can cause a host of problems. These include not only fatigue, weight gain and pain, but also infertility and miscarriages. Iodine deficiency is also a common trigger for breast tenderness and fibrocystic breast disease.
Iodine deficiency used to be epidemic in the US, until it was added to salt and wheat. Though bromide in wheat/bread is banned in many countries as being toxic (it blocks iodine from working), most U.S. bread has stopped using wheat with iodine and is using wheat with bromide instead. Meanwhile, iodine intake in the U.S. has dropped 50% in the last 30 years and toxic bromide intake is increasing. Much to their credit, Pepperidge Farm breads use bromine free flour.
Bottom line? Iodine supplementation is a good idea in general. High-dose iodine is recommended in those with breast cysts or tenderness, unexplained severe fatigue with low body temperature, or thyroid problems.