Exploring the Genetic Link Between Thyroid Dysfunction and Common Psychiatric Disorders: A Specific Hormonal or a General Autoimmune Comorbidity

The causal relationship between major depression disorder and thyroid diseases: A Mendelian randomization study and mediation analysis

BACKGROUND

Studies have been conducted on the relationship between depression and thyroid diseases and function, its causal relationship remains unclear.

METHODS

Using summary statistics of genome-wide association studies of European and East Asian ancestry, we conducted 2-sample bidirectional Mendelian randomization to estimate the association between MDD and thyroid function (European: normal range TSH, T4, T3, fT4, TPOAb levels and TPOAb-positives; East Asian: T4) and thyroid diseases (hypothyroidism, hyperthyroidism, and Hashimoto's thyroiditis), and used Mediation analysis to evaluate potential mediators (alcohol intake, antidepressant) of the association and calculate the mediated proportions.

RESULTS

It was observed a significant causal association between MDD on hypothyroidism (P = 8.94 × 10-5), hyperthyroidism (P = 8.68 × 10-3), and hashimoto's thyroiditis (P = 3.97 × 10-5) among European ancestry, which was mediated by Alcohol intake (alcohol intake versus 10 years previously for hypothyroidism (P = 0.026), hashimoto's thyroiditis (P = 0.042), and alcohol intake frequency for hypothyroidism (P = 0.015)) and antidepressant (for hypothyroidism (P = 0.008), hashimoto's thyroiditis (P = 0.010)), but not among East Asian ancestry (PMDD-hypothyroidism = 0.016, but β direction was different; PMDD-hyperthyroidism = 0.438; PMDD-hashimoto's thyroiditis = 0.496). There was no evidence for bidirectional causal association between thyroid function mentioned above and MDD among both ancestry (all P > 0.05).

CONCLUSION

We importantly observed a significant causal association between MDD on risk of hypothyroidism, hyperthyroidism, and hashimoto's thyroiditis among European ancestry, and Alcohol intake and antidepressant as mediators for prevention of hypothyroidism, hashimoto's thyroiditis attributable to MDD.

Urinary haloacetic acid concentrations and thyroid function among women: Results from the TREE study

BACKGROUND

Disinfection byproducts (DBPs) have been shown to impair thyroid function in experimental models. However, epidemiological evidence is scarce.

METHODS

This study included 1190 women undergoing assisted reproductive technology (ART) treatment from the Tongji Reproductive and Environmental (TREE) cohort from December 2018 to August 2021. Serum thyrotropin (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) were measured as indicators of thyroid function. FT4/FT3 and TSH/FT4 ratios were calculated as markers of thyroid hormone homeostasis. Dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), the two most abundant HAAs, in urine were detected to assess individual DBP exposures.

RESULTS

After adjusting for relevant covariates, positive associations were observed between urinary TCAA concentrations and serum TSH and TSH/FT4 levels (e.g., percent change = 5.82 %, 95 % CI: 0.70 %, 11.21 % for TSH), whereas inverse associations were found for serum FT3 and FT4 (e.g., percent change = -1.29 %, 95 % CI: -2.49 %, -0.07 % for FT3). There also was a negative association between urinary DCAA concentration and serum FT4/FT3 (percent change = -2.49 %, 95 % CI: -4.71 %, -0.23 %). These associations were further confirmed in the restricted cubic spline and generalized additive models with linear or U-shaped dose-response relationships.

CONCLUSION

Urinary HAAs were associated with altered thyroid hormone homeostasis among women undergoing ART treatment.

Air pollution exposure, accelerated biological aging, and increased thyroid dysfunction risk: Evidence from a nationwide prospective study

BACKGROUND

Long-term air pollution exposure is a major health concern, yet its associations with thyroid dysfunction (hyperthyroidism and hypothyroidism) and biological aging remain unclear. We aimed to determine the association of long-term air pollution exposure with thyroid dysfunction and to investigate the potential roles of biological aging.

METHODS

A prospective cohort study was conducted on 432,340 participants with available data on air pollutants including particulate matter (PM2.5, PM10, and PM2.5-10), nitrogen dioxide (NO2), and nitric oxide (NO) from the UK Biobank. An air pollution score was calculated using principal component analysis to reflect joint exposure to these pollutants. Biological aging was assessed using the Klemera-Doubal method biological age and the phenotypic age algorithms. The associations of individual and joint air pollutants with thyroid dysfunction were estimated using the Cox proportional hazards regression model. The roles of biological aging were explored using interaction and mediation analyses.

RESULTS

During a median follow-up of 12.41 years, 1,721 (0.40 %) and 9,296 (2.15 %) participants developed hyperthyroidism and hypothyroidism, respectively. All air pollutants were observed to be significantly associated with an increased risk of incident hypothyroidism, while PM2.5, PM10, and NO2 were observed to be significantly associated with an increased risk of incident hyperthyroidism. The hazard ratios (HRs) for hyperthyroidism and hypothyroidism were 1.15 (95 % confidence interval: 1.00-1.32) and 1.15 (1.08-1.22) for individuals in the highest quartile compared with those in the lowest quartile of air pollution score, respectively. Additionally, we noticed that individuals with higher pollutant levels and biologically older generally had a higher risk of incident thyroid dysfunction. Moreover, accelerated biological aging partially mediated 1.9 %-9.4 % of air pollution-associated thyroid dysfunction.

CONCLUSIONS

Despite the possible underestimation of incident thyroid dysfunction, long-term air pollution exposure may increase the risk of incident thyroid dysfunction, particularly in biologically older participants, with biological aging potentially involved in the mechanisms.

Association between hypothyroidism subtypes and major depression: A two-sample Mendelian randomization study

BACKGROUND

The causal relationship between different hypothyroidism subtypes and the risk of major depression (MD) is yet to be fully elucidated. This study aimed to determine if there's a causal relationship between various hypothyroidism subtypes (and related factors) and the risk of MD.

METHODS

This genetic association study utilized a two-sample Mendelian Randomization (MR) approach to explore the causal relationships between various hypothyroidism subtypes and MD risk. Genome-Wide Association Study (GWAS) summary statistics were obtained from the FinnGen and the UK Biobank. Instrumental variables (IVs) were chosen based on single nucleotide polymorphisms (SNPs).

RESULTS

Among the analyzed hypothyroidism subtypes and related factors, "Hypothyroidism, strict autoimmune" (HTCBSA) and "Hypothyroidism, levothyroxin purchases" (HT/LP) demonstrated a statistically significant positive causal relationship with MD, with odds ratios of 1.020 (95 % CI: 1.004-1.037) and 1.022 (95 % CI: 1.005-1.040), respectively. The sensitivity analysis supported the robustness of these findings, showing no significant horizontal pleiotropy and confirming the stability of results when individual SNPs were removed. "Congenital iodine-deficiency syndrome/hypothyroidism" (CIDS/HT), "Postinfectious hypothyroidism" (PHT), "Hypothyroidism due to medicaments and other exogenous substances" (HDTDM and OES), "Thyroid Stimulating Hormone" (TSH), "Thyrotropin-releasing hormone" (THRH), and "Hypothyroidism, strict autoimmune, 3 medication purchases required" (HTCBSA/3MPR) showed no significant causal relationship with MD.

LIMITATIONS

The study population was limited to individuals of European ancestry, and there may be certain genetic differences between different ethnic groups.

CONCLUSIONS

This MR study suggests a potential causal relationship between certain hypothyroidism subtypes (specifically HTCBSA and HT/LP) and an increased risk of MD.

Association between ambient air pollution and thyroid hormones levels: A systematic review and meta-analysis

BACKGROUND

Growing studies have focused on the effects of ambient air pollution on thyroid hormones (THs), but the results were controversial. Therefore, a systematic review and meta-analysis was conducted by pooling current evidence on this association.

METHODS

Four databases were searched for studies examining the associations of particulate matter [diameter ≤10 μm (PM10) or ≤2.5 μm (PM2.5)] and gaseous [sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), carbon monoxide (CO)] pollutants with THs levels. Random effects models were used to pool the changes in THs levels with increasing air pollutant concentrations. Subgroup analyses were constructed by region, design, sample size, pollutant concentrations, evaluated methods, and potential risk exposure windows.

RESULTS

A total of 14 studies covering 357,226 participants were included in this meta-analysis. The pooled results showed significant associations of exposure to PM2.5, PM10, NO2, SO2, and CO with decreases in free thyroxine (FT4) with percent changes (PC) ranging from -0.593 % to -3.925 %. PM2.5, NO2, and CO were negatively associated with levels of FT4/FT3 (PC: from -0.604 % to -2.975 %). In addition, results showed significant associations of PM2.5 with hypothyroxinemia and high thyroid-stimulating hormone (TSH). Subgroup analyses indicated that PM2.5 and NO2 were significantly associated with FT4 in studies of Chinese, and similar significant findings were found in studies of PM2.5 and FT4/FT3 in areas with higher concentrations of air pollutants and larger samples. PM2.5 exposure in the first trimester was found to be associated with lower FT4 levels in pregnant women.

CONCLUSION

Our findings suggest that exposure to air pollution is associated with changes in THs levels. Enhanced management of highly polluted areas, identification of harmful components and sources of PM, and protection from harmful exposures in early pregnancy may be of great public health importance for the population's thyroid function.