Researchers in New Zealand studied the effects of taking selenium and iodine on thyroid function. They subdivided a total of 100 seniors into 4 groups: a placebo group, a group taking 100 mcg of selenium, a group taking 80 mcg of iodine, and a group taking both the iodine and selenium.
Supplements were taken for 3 months. At the end of the three months, the researchers measured whole blood glutathione peroxidase activity, serum selenium, thyroid markers, as well as urinary iodine excretion.
They found that taking 80 mcg of iodine reduced iodine deficiency and reduced elevated levels of serum thyroglobulins. Selenium intake improved the function of glutathione peroxidase activity, but taking the supplements together did not produce an additional combined effect.