Effects of iodine and fluorine levels in the environment on thyroid function indicators in Hebei Province, China

The impact of environmental iodine and fluorine levels on thyroid function indicators in a healthy population is of crucial significance for developing scientifically sound prevention and control strategies to safeguard residents' health.

To investigate impacts of iodine and fluorine levels in the environment on thyroid function indicators among a healthy population in Hebei Province, China.

Water samples were collected and the area was divided into six regions based on different iodine and fluorine levels: purely high-iodine area, purely low-iodine area, purely adequate-iodine area, high-iodine high-fluorine area, low-iodine high-fluorine area, and purely high-fluorine area. Probability proportionate sampling was used to select 1-2 administrative villages in each region. In each selected village, residents aged 8 and above who had lived there continuously for at least two years were examined. A thyroid survey was conducted, blood samples were taken to check thyroid function indicators, urinary iodine and fluorine levels were measured, and the proportion of residents consuming iodised salt was recorded.

A total of 2400 residents from six regions were included in the study. There was no significant difference in the general data of the six regions (p > 0.05). However, there were significant differences in the comparisons of Thyroid-Stimulating Hormone (TSH), Free Thyroxine (FT4) and Free Triiodothyronine (FT3) levels (p < 0.05). There was no significant difference in the comparison of the proportion of iodised salt consumption among the six regions (X2/F Value, p = 0.160). TSH was negatively correlated with water iodine levels (r = -0.543, p < 0.05), and positively correlated with water fluorine levels (r = 0.281, p < 0.05). FT4 and FT3 were positively correlated with water iodine levels (r = 0.595, p < 0.05; r = -0.117, p < 0.05), and negatively correlated with water fluorine levels (r = 0.543, p < 0.05; r = -0.486, p < 0.05).

High environmental iodine levels significantly impact thyroid function indicators. Residents in areas with high iodine levels in water sources should take early measures to prevent and control thyroid diseases and undergo regular check-ups.