BTW: Brazil nuts are high in Selenium. Hence Redstar's recommendation of eating Brazil nuts.
This info is from Brocklehurst's Textbook of Geriatric Medicine and Gerontology (SEVENTH EDITION)...
"Normal individuals have been found to have serum concentrations of thyroglobulin of less than 5 μg/L and levels appear to be unaffected by age. Concentrations can be increased in patients with hyperthyroidism, benign nodules, and inflammatory disorders, such as subacute thyroiditis. High levels are found in the majority of patients with thyroid cancer."
Without nodules (either benign or cancerous) or hyperthyroid symptoms, that leaves inflammation. I can recommend eating 2 Brazil nuts a day. See if this lowers your TPOAb and thyroglobulin serum. My TPOAb decreased 15% in 6 months eating Brazil nuts. I also felt a difference starting Brazil nuts. My mood swings and irritability vanished and I was so calm. Worth trying out.
Excerpt from Chris Kresser - Selenium: The Missing Link for Treating Hypothyroidism?...
"One study found that selenium supplementation had a significant impact on inflammatory activity in thyroid-specific autoimmune disease, and reducing inflammation may limit damage to thyroid tissue. (6)
This may be due to the increase in glutathione peroxidase and thioredoxin reductase activity, as well as the decrease in toxic concentrations of hydrogen peroxide and lipid hydroperoxides which result from thyroid hormone synthesis. (7)
Another study followed patients for 9 months, and found that selenium supplementation reduced thyroid peroxidase antibody levels in the blood, even in selenium sufficient patients. (8)"