Effects of Excess Fluoride and Iodide on Thyroid Function and Morphology.

Area of Science:

• Environmental toxicology
• Endocrinology
• Cell biology

Background:

• High iodide exposure is linked to thyroid disease in China.
• The impact of fluoride on thyroid function remains debated.
• Understanding combined fluoride and iodide effects is crucial for public health.

Purpose of the Study:

• To investigate the effects of excess fluoride, alone and combined with iodide, on thyroid gland structure and function.
• To evaluate thyroid hormone levels and histological changes in rats exposed to fluoride and iodide.
• To determine the synergistic or antagonistic effects of combined fluoride and iodide exposure on the thyroid.

Main Methods:

• Wistar rats were exposed to varying levels of fluoride (15-60 ppm) and iodide (1200 μg/L), alone or in combination.
• Thyroid gland structure was assessed using Hematoxylin and eosin staining and transmission electron microscopy.
• Serum concentrations of thyroid hormones (TT3, TT4) and pituitary hormone (TSH) were measured.

Main Results:

• Iodide exposure increased colloid lumen area and decreased epithelial cell/nuclear diameters.
• Fluoride exposure increased nuclear diameters.
• Combined fluoride and iodide exposure caused the most dramatic damage to follicular epithelial cells.
• Certain fluoride groups showed reduced TT3 and TT4 levels, but TSH remained unchanged.

Conclusions:

• Iodide is the primary cause of thyroid damage, but fluoride significantly promotes specific functional and morphological changes.
• Fluoride can exacerbate iodide-induced thyroid alterations, impacting follicular epithelial cells.
• Combined exposure to fluoride and iodide poses a greater risk to thyroid health than individual exposures.