Patients with Graves' disease respond better to their treatment if their diet contains plenty of iodine than if it contains little iodine. This is evident from a Chinese trial published in Clinical Endocrinology in 2018.

Study
Endocrinologists at Fujian Medical University conducted a study on 405 people diagnosed with Graves' disease. In this disease, the immune system mimics the action of the hormone TSH, causing the thyroid gland to produce too much thyroid hormone.

The standard treatment after diagnosis is medication with methimazole, a substance that drastically reduces thyroid hormone synthesis, for a year. Doctors then determine whether the immune system has returned to normal.

In their study, the researchers removed all major sources of iodine from the subjects' diets. This usually means eliminating seafood, shellfish, dairy, seaweed, and eggs from the diet.

Such an adjustment seems logical at first glance. The thyroid gland needs iodine for thyroid hormone biosynthesis. Less iodine means less thyroid hormone. Let's call that Theory A.

But on closer inspection, such an intervention might also be counterproductive. If the thyroid gland has insufficient iodine available for thyroid hormone production, the pituitary gland might produce more TSH. And that's exactly what you don't want. For convenience, we'll call this theory B.

Because they wanted to know which theory was correct, the endocrinologists gave half of their subjects only a low-iodine diet. If we were to make a rough estimate based on the study data, we think this group received 45-90 micrograms of iodine daily. That's lower than the 150 micrograms per day that most nutritional scientists recommend we consume daily.

The other half also received a low-iodine diet, but also table salt enriched with iodine. This salt provided this group of subjects with an additional 200 micrograms of iodine daily. We estimate their iodine intake at 200-300 micrograms per day. This intake falls just short of what nutritionists consider 'mildly excessive'.

Results
The researchers treated their subjects with methimazole for one year. They then stopped the treatment and monitored the disease recurrence for a year.

In the iodine-reduced group, this was the case for 45.5 percent of the subjects, and in the iodine-rich group, this occurred for 35.5 percent. This difference was statistically significant. Therefore, an iodine-rich diet increases the chance of successful treatment by 18 percent.

The researchers monitored the concentration of TRAb antibodies in the blood of their subjects. These antibodies mimic the action of TSH and simultaneously attack the thyroid gland. In Graves' disease, doctors prefer to see the TRAb concentration below 1.75.

The TRAB concentration decreased in both groups, but it was more significant in the group on an iodine-rich diet.