Study On The Association Between PM_2.5 Exposure And TSH Variability Among Reproductive-aged Women In China

Objective:To exploration of the association between PM_2.5 exposure and TSH variability in women of reproductive age provides a theoretical basis for the development of health policies.Methods:This study selected 31,893,942 women of reproductive age who participated in the National Free Pre-pregnancy Checkups Project from 2013 to 2020as the research subjects,with the participants in each county（district）during a natural week as the observation units.The PM_2.5 measured by the monitoring station of the observation unit was used as the main exposure,and the TSH of the participants in the observation unit was used as the main outcome.The mean,standard deviation,coefficient of variation,interquartile range,and variation independent of mean were calculated for the exposure and outcome indicators.A generalized linear regression model with multiple adjustments was used to evaluate the association between PM_2.5and TSH under different exposure windows（cumulative lag of 0 weeks,4 weeks,and1 year）,and the results were expressed using the percentage change in the strength of the association and its 95%confidence interval.At the same time,restricted cubic splines were used to estimate the exposure-response relationship between PM_2.5 and TSH under different exposure windows and different variability indicators to reveal the non-linear relationship between the two.Results:1.The association between PM_2.5 mean and TSH mean,standard deviation,coefficient of variation and interquartile range is negatively correlated,while the association between PM_2.5 and TSH variation independent of mean is positively correlated.For every 10μg/m³ increase in PM_2.5 mean exposure at lag 0 week,TSH mean,standard deviation,coefficient of variation and interquartile range decreased by0.38%（95%CI:0.36%,0.41%）,0.44%（0.40%,0.49%）,0.07%（0.04%,0.11%）,and0.28%（0.23%,0.33%）,respectively.TSH variation independent of mean increased by0.11%（0.07%,0.15%）.2.The association between PM_2.5 variability and TSH standard deviation and coefficient of variation is negatively correlated,while the association between the PM_2.5coefficient of variation and the mean and variance indicators of TSH is mostly positive is positively correlated.For a 10μg/m³ increase in PM_2.5 exposure standard deviation at cumulative lag 0 weeks,TSH standard deviation and coefficient of variation decrease by 0.11%（95%CI:0.02%,0.20%）and 0.27%（95%CI:0.20%,0.33%）,respectively.TSH standard deviation and coefficient of variation decreased by 0.09%（0.03%,0.16%）and 0.19%（0.14%,0.24%）,respectively,for each 10μg/m³ increase in cumulative lag0 weeks PM_2.5 exposure interquartile spacing.For a 10%increase in PM_2.5 exposure coefficient of variation at cumulative lag 0 weeks,TSH mean,standard deviation,interquartile range and variation independent of mean increase by 0.18%（95%CI:0.14%,0.23%）,0.24%（95%CI:0.15%,0.33%）,0.13%（95%CI:0.03%,0.23%）and0.45%（0.38%,0.53%）,respectively,while the TSH independent of mean variation increases by 0.45%（95%CI:0.38%,0.53%）.3.The association between of PM_2.5 variation independent of mean with TSH mean and variability indicators in observation units is positively associated.For a lag of 0 weeks,each 10%increase in PM_2.5 exposure variation independent of mean is associated with an increase in TSH mean,standard deviation,and interquartile range by 0.20%（95%CI:0.17%,0.23%）,0.57%（95%CI:0.52%,0.63%）,and 0.38%（95%CI:0.31%,0.44%）,respectively.TSH variability measures,including standard deviation and variation independent of mean,increase by 0.38%（95%CI:0.34%,0.42%）and 0.93%（95%CI:0.88%,0.98%）,respectively.4.As the exposure window of the cumulative lag is extended,the correlation between the change in PM_2.5 exposure per unit of observation and the mean and variability of TSH is largely consistent with that at the cumulative lag of 0 weeks,and is further enhanced at the cumulative lag of 1 year.The exposure-response relationship showed that as PM_2.5 exposure increased,the levels and variability indices of TSH mostly decreased,and the sensitivity analysis results were consistent with this.As PM_2.5exposure variability increased,the trend of changes in TSH standard deviation and quartile range was first a decrease followed by fluctuation and then a decrease,while the trend of changes in TSH coefficient of variation and variation independent of mean was first a decrease followed by an increase.Conclusion:1.This study reveals a negative association between PM_2.5 exposure and TSH levels,exhibiting a non-linear exposure-response relationship in different exposure windows.Additionally,the association shows cumulative effects across different exposure windows,providing scientific evidence for further understanding the impact of air pollution on human health.2.There is a correlation between PM_2.5 exposure variability and TSH variability indicators in the adult population,with a non-linear exposure-response relationship observed in different exposure windows.PM_2.5 exposure induces changes in TSH indicators even at low concentration levels,and as the exposure concentration increases,this association becomes complex and diverse.These findings suggest that physiological adaptation mechanisms may play a role in the changes of PM_2.5 exposure variability and TSH variability indicators.3.This study contributes to the evidence of PM_2.5 exposure perturbing thyroid function in the adult population.Further related experimental and toxicological research is recommended to clarify the precise mechanisms underlying the exposure-outcome relationship.It is advised that susceptible individuals reduce their exposure to polluted environments to protect their own health and the health of future generations.Governments should implement measures to control pollution and reduce the emissions of harmful substances such as PM_2.5,thereby safeguarding the physical health and life safety of the general public.