I consider hyperthyroidism and hypothyroidism (including Graves' disease and Hashimoto's thyroiditis) as different phases of the same disease. I'm quite confident that both are caused by nutrient deficiencies, but hyperthyroidism is the result when the deficiencies become more severe.
More info at the link, including self-tests for hypo and hyperthyroidism.
Symptoms of Hypothyroidism (An underactive thyroid)
feeling run down and sluggish
difficulty concentrating, brain fog
unexplained or excessive weight gain
dry, coarse and/or itchy skin
dry, coarse and/or thinning hair
feeling cold, especially in the extremities
increased menstrual flow
more frequent periods
Symptoms of Hyperthryodisim (An overactive thyroid)
thinning of your skin
fine brittle hair
muscular weakness especially involving the upper arms and thighs
more frequent bowel movements
weight loss despite a good appetite
lighter flow, less frequent menstrual periods
LIST OF NUTRIENTS FOR HYPERTHYROIDISM AND HYPOTHYROIDISM
(Warning: Use this list with caution and get advice from your physician before using these recommended supplements. The recommended amounts of these nutrients are for experimental purposes only and the potential effects of these nutrients on your health are unknown. You must be responsible for your own health and for knowing the consequences of taking these recommended supplements. I think these are reasonable amounts of these nutrients, but I am not a physician and do not know your health situation. This list is only my best guess about what might help these diseases. What has helped me or another person may cause adverse reactions in you. Consult your own physician.)
Hypers: Everything that I've experienced myself, seen in others, and read about in scientific studies indicates that the primary deficiencies involved in hyperthyroidism are copper and iron. The balance between copper and zinc seems to be critically important in determining the rate of thyroid hormone production. Copper slows down the thyroid while zinc increases thyroid action. Copper should be supplemented first and if zinc is presently being supplemented it should be discontinued for two to three weeks or until the thyroid slows down. Copper absorption and utilization is increased by molybdenum and the B-complex vitamins, including extra biotin and PABA. Zinc is essential for health but excess amounts may increase thyroid hormone production. You will have to experiment to determine how much zinc you can take. Try to maintain a zinc/copper ratio of about 3:1 to 5:1 at first.
Most hypers and hypos are deficient in iron. Iron may be low because of insufficient intake or deficiencies of minerals such as manganese, copper, or cobalt (vitamin B-12), or B vitamins, which are essential for iron utilization. Copper and iron work together to form hemoglobin and need to be supplemented together. Supplementing with either alone can lead to a deficiency of the other.
Studies show that a deficiency of selenium usually causes a decrease in the conversion of T4 to T3. However under abnormal conditions, a deficiency of selenium can cause the body to increase conversion of T4 to T3 which can lead to higher levels of T3. Selenium is very important for normal thyroid function. Start by taking 100 micrograms per day and gradually increase up to 300 micrograms.
All of the supplements listed are necessary either to correct the underlying causes of hyperthyroidism or to supplement nutrients which are used up by the hyper metabolism.
HYPOS: Many nutrient deficiencies may cause hypothyroidism. The two main nutrients which may be deficient are selenium and zinc. Selenium may become deficient if there are excessive amounts of toxic metals being ingested, such as mercury from silver Amalgam dental fillings. The more mercury or other toxic metals ingested, the more selenium you'll need. Start with 200 micrograms of selenium and work up to 400 micrograms. You may need more selenium if you have many amalgam fillings. The B-complex vitamins, especially B-6, facilitate zinc metabolism. Also the amino acid L-cysteine is important in zinc metabolism. Iron, manganese, and chromium are often deficient in hypos. Some hypos may be so deficient in minerals that they are close to becoming hyper. If you are experiencing nighttime rapid heart beat, then you are close and should also supplement with copper.