It really depends. Supplementing iodine without selenium can make Hashimoto's worse but what is worth emphasising that a lot of people with Hashimoto's and hypothyroidism are deficient in iodine. Best and safest way is to do urine iodine test first as iodine from hair tissue mineral analysis may not be that accurate. Click here to read more about iodine and how important it is not only for thyroid but also for breast and ovaries.