Researchers in Australia studied women six months after their pregnancy and found that those who had the lowest levels of iodine were four times more likely to have developed hypothyroidism two years later. The researchers followed some of the women for 12 years, and found iodine levels were an excellent predictor of who did and didn’t end up with long term hypothyroidism. Most of those with low levels did, while most of those with normal levels didn’t. Thyroid deficiency from low iodine may sometimes be reversed by simply taking iodine!
"Low urinary iodine postpartum is associated with hypothyroid postpartum thyroid dysfunction and predicts long-term hypothyroidism." Stuckey BG, Kent GN, Allen JR, Ward LC, Brown SJ, Walsh JP. Clin Endocrinol (Oxf). 2011 May;74(5):631-5. doi: 10.1111/j.1365-2265.2011.03978.x.