Introduction: Fluoride in drinking water is known to exert both beneficial and detrimental effects on health. When consumed in excess, it is known to cause adverse effects including dental fluorosis, hip fracture, bone cancer, lower intelligence, and kidney toxicity plus goiter.
Aim: This study was carried out to determine the histological changes that might occur on thyroid follicular cells after the administration of sodium fluoride and evaluate their reversibility.
Materials and methods: To conduct the experiment, 30 healthy adult male albino rats were randomly divided into three groups: group I (control group), group II (experimental group), which received sodium fluoride water (200 ppm) daily through an orogastric tube for 1 month, and group III (withdrawal group), which received sodium fluoride water similar to group II, and were then killed 1 month after fluoride withdrawal. Rats were killed under ether anesthesia and blood samples were subjected to hormonal assays of T3, T4, and TSH thyroid stimulating hormone. The thyroid gland tissue samples were removed and processed for light microscopic examination of toluidine blue-stained semithin sections and electron microscopic examination (TEM).
Results: Sodium fluoride significantly decreased T3, T4, and TSH levels in group II, which did not revert to normal levels in group III. Examination of semithin sections of thyroid glands of group II showed distension of follicles that were lined with flattened cells. Most of the follicles showed shedding of the epithelial lining and others showed focal stratification with papillary formation. Follicular cells had dark pyknotic nuclei and vacuolated cytoplasm. Ultrastructural changes included loss of apical microvilli, dilated rER rough endoplasmic reticulum, many lysosomes, irregular dark nuclei, focal loss of epithelial lining or focal proliferation, and papillary formation. Group III showed the same changes as the control group, which indicated no recovery.
Conclusion: The results of this study question the validity of fluoridation of drinking water, milk, fruit juices, and salt by public health authorities and also the steps taken to prevent the side effects of excess fluorine and iodine deficiencies in endemic fluorosis areas.