After reviewing ultrasound tests on 186 children, researchers came to the conclusion that weight might be linked to structural changes in the thyroid.
The study has been published in the Journal of Clinical Endocrinology and Metabolism.
According to scientists, obesity may be causing thyroid disorders, not the reverse.
It is not yet clear whether losing weight could solve the problem.
Obesity may cause inflammation that damages the thyroid, Dr. Giorgio Radetti of the Regional Hospital of Bolzano in Italy and colleagues said.
"The ultrasound findings are a bit mysterious, but do suggest the existence of a low-grade inflammation state, which has been known to characterise obesity. Our study shows that alterations in thyroid function and structure are common in obese children and we may have uncovered the link," BBC quoted the expert, as saying.
"We found an association between body mass index and thyroid hormone levels which suggests that fat excess may have a role in thyroid tissue modification," the researcher added.