Six Air Pollutants Associated With Increased Risk of Thyroid Nodules: A Study of 4.9 Million Chinese Adults

Associations between short-term exposure to air pollution and thyroid function in a representative sample of the Korean population

BACKGROUND

Disruption of thyroid function can profoundly affect various organ systems. However, studies on the association between air pollution and thyroid function are relatively scarce and most studies have focused on the long-term effects of air pollution among pregnant women.

OBJECTIVES

This study aimed to explore the associations between short-term exposure to air pollution and thyroid function in the general population.

METHODS

Data from the Korea National Health and Nutrition Examination Survey (2013-2015) were analyzed (n = 5,626). Air pollution concentrations in residential addresses were estimated using Community Multiscale Air Quality models. The moving averages of air pollution over 7 days were set as exposure variables through exploratory analyses. Linear regression and quantile g-computation models were constructed to assess the effects of individual air pollutants and air pollution mixture, respectively.

RESULTS

A 10-ppb increase in NO2 (18.8-μg/m3 increase) and CO (11.5-μg/m3 increase) was associated with 2.43% [95% confidence interval (CI): 0.42, 4.48] and 0.19% (95% CI: 0.01, 0.36) higher thyroid-stimulating hormone (TSH) levels, respectively. A 10-μg/m3 increase in PM2.5 and a 10-ppb increase in O3 (19.6-μg/m3 increment) were associated with 0.87% (95% CI: 1.47, -0.27) and 0.59% (95% CI: 1.18, -0.001) lower free thyroxine (fT4) levels, respectively. A simultaneous quartile increase in PM2.5, NO2, O3, and CO levels was associated with lower fT4 but not TSH levels.

CONCLUSIONS

As the subtle changes in thyroid function can affect various organ systems, the present results may have substantial public health implications despite the relatively modest effect sizes. Because this was a cross-sectional study, it is necessary to conduct further experimental or repeated-measures studies to consolidate the current results.

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.

Risk factors associated with the prevalence of thyroid nodules in adults in Northeast China: a cross-sectional population-based study

OBJECTIVES

This study examined the association between anthropometric measurements, lifestyle factors and the prevalence of thyroid nodules among adults in Northeast China.

DESIGN

We employed a cross-sectional approach involving a questionnaire survey, which focused on participants' living habits, and a physical examination that included anthropometry and ultrasound imaging.

SETTING

The data were procured during multiple trips by medical teams from the first hospital of China Medical University to towns in Northeast China.

PARTICIPANTS

Of the 1092 participants, 489 did not have thyroid nodules (mean age: 54.02±11.49 years; 297 females (60.7%)), 99 had single thyroid nodules (mean age: 58.19±10.77 years; 59 females (59.6%)) and 504 had multiple thyroid nodules (mean age: 60.05±10.68 years; 394 females (78.2%)). Inclusion criteria mandated participants be over 20 years old without other medical conditions. We excluded individuals who had undergone surgical resection for thyroid nodules.

RESULTS

The prevalence of thyroid nodules was significantly associated with being female (OR 2.569, 95% CI 1.937 to 3.405, p<0.001) and increased age (OR 1.054, 95% CI 1.041 to 1.066, p<0.001). This association was more pronounced in those with multiple thyroid nodules. For males under 60, non-smoking was inversely correlated with the prevalence of multiple thyroid nodules (OR 0.321, 95%CI 0.149 to 0.69, p<0.05). For females under 60, diastolic blood pressure (DBP) was significantly linked with the prevalence of thyroid nodules (OR 0.978, 95% CI 2.614 to 2.705, p<0.05).

CONCLUSIONS

Besides gender and age, the prevalence of thyroid nodules in Northeast China correlates with smoking habits and DBP.

Effects of the abdominal fat distribution on the relationship between exposure to air pollutants and thyroid hormones among Korean adult males

BACKGROUND

Several significant associations between air pollution and thyroid function have been reported, but few studies have identified whether these associations differ by obesity, particularly its regional distribution. We assessed the relationship between ambient air pollution and thyroid hormone, and whether this relationship is modified by abdominal adiposity, as indicated by the waist circumference, visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), and visceral-to-subcutaneous fat ratio (VSR) in Korean men.

METHODS

We included 2440 male adults in the final analysis and used each person's annual average exposure to four air pollutants: particulate matter with an aerodynamic diameter ≤ 10 μm (PM10), nitrogen dioxide, sulfur dioxide (SO2), and carbon monoxide (CO). Abdominal fat deposition was quantified by computed tomography. Serum thyrotropin (TSH) and free thyroxine (FT4) concentrations were measured for thyroid hormone. To evaluate the relationship between air pollution and thyroid hormone according to adiposity, we performed multiple linear regression analysis on the two subgroups stratified by abdominal fat level.

RESULTS

Abdominal adiposity was significantly related to FT4 concentration. The exposures to air pollutants were associated with increased TSH and decreased FT4 concentrations. In stratified analysis using abdominal fat traits, ambient air pollution except for SO2 was significantly related to increased TSH and decreased FT4 concentrations in the high adiposity group (all p < 0.05), but not in the normal adiposity group. Among the air pollutants, PM10 showed an association with an increase of TSH concentration in all group with high adiposity, including high VAT, high SAT, and high VSR groups (all p < 0.05). In case of FT4, CO showed a similar pattern. Among the abdominal fat-related traits, the VSR in the high adiposity group had the largest effect on the relationship between exposure to air pollutants and thyroid hormone.

CONCLUSIONS

This study suggests the first clue that the relationship between air pollution exposure and thyroid hormone differs according to abdominal fat distribution among Korean adult males.

Environmental factors and incidence of thyroid cancer in the world (1990-2019): an ecological study

Thyroid cancer (TC) is the most common endocrine malignancy. Environmental risk factors such as presence of pollutants in air as well as the combustion of fossil fuels or carbon as a cooking habit in closed environments inside houses affect thyroid hormonal homeostasis and diseases. This study aimed to estimate the association between environmental risk factors and the incidence of thyroid cancer worldwide from 1990 to 2019 including particulate pollutants coming from fossil fuels employed in closed environments. Data on the incidence of thyroid cancer and some environmental risk factors were extracted from the Global Cancer Observatory (GLOBOCAN) for 204 countries and territories from 1990 to 2019. Pearson's correlation coefficient was used to determine the correlation between the thyroid cancer incidence and environmental risk factors. Finally, a generalized additive model was fitted for modeling. R 3.5.0 was used for analysis of the data. The most relevant results showed that the age-standardized incidence rate (ASIR) of thyroid cancer has a positive and significant correlation with environmental air pollution by O3 (r=0.63, P value<0.001), by particulate matter pollution (r=0.23, P value<0.001), and by household PM2.5 air pollution (r=0.52, P value≤0.001). In contrast, the correlation between ASIR and high temperature (T>25.6°C) (r=-0.27, P value<0.001) is negative and significant. The modeling results showed that particulate matter pollution and O3 pollution and household PM2.5 air pollution which originated from solid fuels are risk factors for thyroid cancer. Therefore, more research in this field is necessary in areas with high levels of air pollution at the national and international levels.

Impact of social and economic factors on global thyroid cancer incidence and mortality

PURPOSE

The incidence of thyroid cancer has increased substantially over the past few decades and is partially explained by overdiagnosis. Geographical variations in incidence rates were reported to be related to national development status. This study aimed to gain deeper insights into global thyroid cancer burden by incorporating additional social and economic factors to account for cross-national disparities.

METHODS

We performed a multivariate analysis of age-standardized incidence and mortality data from the GLOBOCAN 2020 database for 126 countries that had more than 100 incident cases of thyroid cancer. The human development index (HDI), current health expenditure, and additional Global Health Observatory indicators were extracted from multiple sources.

RESULTS

Age-standardized incidence was highly correlated with HDI (standardized coefficient beta = 0.523, 95% confidence interval [CI] = 0.275-0.771) among the countries studied. The prevalence of raised fasting blood glucose was associated with age-standardized mortality (beta = 0.277, 95% CI = 0.038-0.517). Generally, the mortality-to-incidence ratio was higher in males than in females. In multivariate analysis, HDI (beta = - 0.767, 95% CI = - 0.902 to - 0.633), current health expenditure (beta = 0.265, 95% CI = 0.137-0.394), and fine particulate matter (PM2.5) concentrations (beta = 0.192, 95% CI = 0.086-0.298) were associated with mortality-to-incidence ratios.

CONCLUSIONS

National developments gauged by HDI explain the majority of the variation in incidence rates of thyroid cancer but play a smaller role in disparities in mortality rates. The association between air pollution and thyroid cancer outcomes warrants further investigation.

Type 2 diabetes and thyroid cancer: Synergized risk with rising air pollution

Diabetes is a complex condition, and the causes are still not fully understood. However, a growing body of evidence suggests that exposure to air pollution could be linked to an increased risk of diabetes. Specifically, exposure to certain pollutants, such as particulate Matter and Ozone, has been associated with higher rates of diabetes. At the same time, air pollution has also been linked to an increased risk of thyroid cancer. While there is less evidence linking air pollution to thyroid cancer than to diabetes, it is clear that air pollution could have severe implications for thyroid health. Air pollution could increase the risk of diabetes and thyroid cancer through several mechanisms. For example, air pollution could increase inflammation in the body, which is linked to an increased risk of diabetes and thyroid cancer. Air pollution could also increase oxidative stress, which is linked to an increased risk of diabetes and thyroid cancer. Additionally, air pollution could increase the risk of diabetes and thyroid cancer by affecting the endocrine system. This review explores the link between diabetes and air pollution on thyroid cancer. We will discuss the evidence for an association between air pollution exposure and diabetes and thyroid cancer, as well as the potential implications of air pollution for thyroid health. Given the connections between diabetes, air pollution, and thyroid cancer, it is essential to take preventive measures to reduce the risk of developing the condition.

UV radiation and air pollution as drivers of major autoimmune conditions

Autoimmune diseases comprise a very heterogeneous group of disorders characterized by disruptive immune responses against self-antigens, chronic morbidity and increased mortality. The incidence and prevalence of major autoimmune conditions are particularly high in the western world, at northern latitudes, and in industrialized countries. This study will mainly focus on five major autoimmune conditions, namely type 1 diabetes, multiple sclerosis, inflammatory bowel diseases, rheumatoid arthritis, and autoimmune thyroid disorders. Epidemiological and experimental evidence suggests a protective role of sunlight exposure on the etiology of major autoimmune conditions mediated by the endogenous production of vitamin D and nitric oxide. A historical perspective shows how the rise of anthropogenic air pollutants is temporally associated with dramatic increases in incidence of these conditions. The scattering caused by ambient particulate matter and the presence of tropospheric ozone can reduce the endogenous production of vitamin D and nitric oxide, which are implicated in maintaining the immune homeostasis. Air pollutants have direct detrimental effects on the human body and are deemed responsible of an increasingly higher portion of the annual burden of human morbidity and mortality. Air pollution contributes in systemic inflammation, activates oxidative pathways, induces epigenetic alterations, and modulates the function and phenotype of dendritic cells, Tregs, and T-cells. In this review, we provide epidemiological and mechanistic insights regarding the role of UV-mediated effects in immunity and how anthropic-derived air pollution may affect major autoimmune conditions through direct and indirect mechanisms.

Socioeconomic disparity in the association between fine particulate matter exposure and papillary thyroid cancer

BACKGROUND

Limited data exists suggesting that cumulative exposure to air pollution in the form of fine particulate matter (aerodynamic diameter ≤ 2.5 μm [PM2.5]) may be associated with papillary thyroid carcinoma (PTC), although this relationship has not been widely established. This study aims to evaluate the association between PM2.5 and PTC and determine the subgroups of patients who are at the highest risk of PTC diagnosis.

METHODS

Under IRB approval, we conducted a case-control study of adult patients (age ≥ 18) newly diagnosed with PTC between 1/2013-12/2016 across a single health care system were identified using electronic medical records. These patients were compared to a control group of patients without any evidence of thyroid disease. Cumulative PM2.5 exposure was calculated for each patient using a deep learning neural networks model, which incorporated meteorological and satellite-based measurements at the patients' residential zip code. Adjusted multivariate logistic regression was used to quantify the association between cumulative PM2.5 exposure and PTC diagnosis. We tested whether this association differed by gender, race, BMI, smoking history, current alcohol use, and median household income.

RESULTS

A cohort of 1990 patients with PTC and a control group of 6919 patients without thyroid disease were identified. Compared to the control group, patients with PTC were more likely to be older (51.2 vs. 48.8 years), female (75.5% vs 46.8%), White (75.2% vs. 61.6%), and never smokers (71.1% vs. 58.4%) (p < 0.001). After adjusting for age, sex, race, BMI, current alcohol use, median household income, current smoking status, hypertension, diabetes, COPD, and asthma, 3-year cumulative PM2.5 exposure was associated with a 1.41-fold increased odds of PTC diagnosis (95%CI: 1.23-1.62). This association varied by median household income (p-interaction =0.03). Compared to those with a median annual household income <$50,000, patients with a median annual household income between $50,000 and < $100,000 had a 43% increased risk of PTC diagnosis (aOR = 1.43, 95%CI: 1.19-1.72), and patients with median household income ≥$100,000 had a 77% increased risk of PTC diagnosis (aOR = 1.77, 95%CI: 1.37-2.29).

CONCLUSIONS

Cumulative exposure to PM2.5 over 3 years was significantly associated with the diagnosis of PTC. This association was most pronounced in those with a high median household income, suggesting a difference in access to care among socioeconomic groups.

Effect of the Marine Exercise Retreat Program on Thyroid-Related Hormones in Middle-Aged Euthyroid Women

This study aimed to investigate the effects of a marine exercise retreat program on thyroid-related hormone levels. A total of 62 middle-aged euthyroid women participated in a 6-day marine exercise retreat program. Using thyroid-stimulating hormone (TSH) and free thyroxine (fT4) hormone levels, the participants were divided into high and low-hormone-level groups. Despite decreased TSH and fT4 levels after the program, the factors influencing changes in each group were different. TSH levels were influenced by changes in the normalized low frequency (nLF) of heart rate variability and carbon monoxide (CO) from all the participants, and changes in body fat percentage, nLF, and nitrogen dioxide (NO2) exposure level in the high TSH group. fT4 levels were influenced by changes in body mass index (BMI), NO2 exposure, and particulate matter diameter of 10 µm or less (PM10) exposure in all participants. Changes in BMI and CO exposure influenced the low fT4 group. Lastly, changes in the exercise stress test affected the high fT4 group. Thus, the marine exercise retreat program affected euthyroid thyroid-related hormone levels, and influencing factors differ depending on the initial value of the hormone.