The effect of the deficiency of the microelement iodine in the environment on the thyroid gland

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Currently, the problem of iodine deficiency is still relevant. The President of the fgbi "SMRC endocrinology" of Minzdrav of Russia, academician of the RAS I. I. Dedov and his team are one of the main initiators of the bill on prevention of iodine deficiency using iodized salt. However, this question is still open. At the same time, iodine deficiency in the environment and the diseases caused by it form a wide range of medical and social problems [1]. Iodine deficiency in the biosphere is a little-changing factor [1], which leads to a decrease in the content of this trace element in food, and people who consume them suffer from iodine deficiency [2]. The population of most countries of the world, including the Russian Federation, is experiencing iodine deficiency and is at risk of developing iodine deficiency diseases [2]. Iodine deficiency Mamonov Yu. P. with co-authors is called a dangerous environmental phenomenon [1]. In conditions of iodine deficiency, the risk of thyroid cancer increases tenfold [3]. Therefore, the identification of the consequences of iodine deficiency on the thyroid gland is relevant.
The AIM is to form a holistic view of the impact of the deficiency of the trace element iodine in the environment on the thyroid gland by assessing the incidence of thyroid pathology in the Voronezh region.
MATERIALS AND METHODS
Research design. The structure of all thyroid diseases in the Voronezh region was studied on the basis of the absolute values indicated in the form of federal statistical observation No. 12 "Information on the number of diseases registered in patients living in the service area of a medical organization" from 2013 to 2019 inclusive. Based on the data of form No. 12 and information from Voronezhstat [4] on the population size, the primary and general incidence of thyroid pathology was calculated. The analysis of morbidity indicators was performed in children from 0 to 14 years, adolescents from 15 to 17 years, adults 18 years and older. Statistical methods allowed us to assess the dynamics of morbidity indicators.
Compliance criteria. The study included male and female patients living in the Voronezh region who were diagnosed with thyroid damage, including due to iodine deficiency in the environment. Patients were divided into three age groups: children (0-14 years), adolescents (15-17 years) and adults (18 years and older).
Terms of the event. The statistical data included indicators of inpatient and outpatient medical care in all districts of the Voronezh Region and the city of Voronezh.
Duration of the study. The data of the statistical form No. 12 were analyzed retrospectively from 2013 to 2019.
Description of the medical intervention. Using official statistics, the initial incidence (the number of newly reported cases for the year to the average population, multiplied by 100,000 people) and the overall incidence (the number of all registered cases of illness to the average population, multiplied by 100,000). When calculating the incidence, the indicators of the average annual population were taken on the basis of data from Voronezhstat [4] in accordance with the previously designated age groups.
The main outcome of the disease. At the first stage of the work, the structure of thyroid diseases in the Voronezh Region was studied, official statistics were collected, and the incidence rates per 100,000 people were calculated. At the second stage, to analyze the dynamics of the incidence of thyroid pathology, linear regression models were constructed, the angles of the trend lines were calculated, and the Student's t-test was used to identify the significance of the k coefficients, while the indicator was considered reliable at p<0.05.
Analysis in subgroups. The analysis was performed in three groups presented in Form No. 12: children, adolescents and adults. On the basis of form No. 12, it is not possible to fully identify a group of patients with iodine deficiency diseases. Data on patients with subclinical hypothyroidism includes information on both patients with subclinical hypothyroidism due to iodine deficiency, and on patients who have identified other causes of hypothyroidism. Data on patients with thyrotoxicosis includes information on both patients with iodine-induced thyrotoxicosis and patients with other causes of thyrotoxicosis. Since 2014 the group of patients with other forms of non-toxic goiter included patients with non-toxic diffuse, nodular, and multi-nodular goiter. It has become impossible to study the incidence separately in nodular forms of goiter. Therefore, we calculated the incidence jointly in patients with endemic goiter associated with iodine deficiency and other forms of non-toxic goiter. Given that among patients with subclinical hypothyroidism and thyrotoxicosis there are patients whose cause of pathology is associated with iodine deficiency, we also calculated the incidence in these nosologies. The analysis of the incidence of patients with congenital iodine deficiency syndrome was made only in children from 0 to 14 years old.
Methods for registering outcomes. The slope angle of the trend line (coefficient k) was considered reliable (the presence of dynamics) at p<0.05.
Ethical expertise. The design of the work does not provide for the study of the research protocol by the ethics committee.
Statistical analysis. Principles for calculating the sample size: no preliminary calculation of the sample size was carried out, since it was dictated by the number of people living in the Voronezh region during the study period and having thyroid pathology. Methods of statistical data analysis. Using the initial statistical data, we constructed linear regression models describing the dynamics of the studied indicators, calculated the slope angles of the trend lines (coefficient k is a quantitative expression of the dynamics of morbidity), and estimated the significance of the k coefficients using the Student's t-test: the coefficients were considered reliable (the presence of dynamics) at p<0.05. During statistical processing, Microsoft Excel 2010 and Statistica 8.0 programs were used.
RESULTS
Objects (participants) of the study. The patient data is taken from the federal statistical observation form No. 12. The sample size was 158,651 cases. Of these, in 2013 – 17081 cases, in 2014 - 19572, in 2015-21738, in 2016 – 23028, in 2017 – 25233, in 2018 – 26634 and in 2019 – 25365 cases. The arithmetic mean value (M) was 22664 cases. The presented sample included persons of both sexes living in the Voronezh Region.
The main results of the study. The analysis of the dynamics of the overall morbidity in children aged 0-14 years with endemic goiter and other forms of non-toxic goiter showed that there has been a steady decline in this indicator since 2013, on average, by 18,445 cases per 100,000 children per year (k = -18,445), which is consistent with the indicators of the primary incidence of goiter (p = -17,686), since 2015.. However, this trend was not assessed as reliable due to a significant sharp decline in the indicator in 2014 and 2016. Among adolescents aged 15-17 years, the overall incidence of endemic goiter and other forms of non-toxic goiter decreases (k =-85,313), which is also consistent with the data on primary morbidity: there is a significant decrease in the incidence, on average, by 96,008 cases per 100,000 adolescents per year (k=-96,008 at p=0.0115). The obtained results demonstrate that the primary morbidity rate in children and adolescents of the Voronezh Region has not reached a sporadic level and is higher than the indicator for the Russian Federation [6] despite the revealed downward trend. This is due to the fact that the preventive measures carried out among this category of the population are still not sufficient and need to be strengthened. In the case of endemic goiter and other forms of non-toxic goiter among the adult population from 2013 to 2019 in the Voronezh Region, the average total incidence rate was 843 cases per 100,000 people, the primary incidence rate was 95.91 cases per 100,000 people, which is lower than the Russian average of 931 and 144 cases per 100,000 people, respectively [5]. At the same time, if in the Russian Federation the adult population has a statistically significant decrease in morbidity, then in the Voronezh region there is a statistically significant increase in both the general morbidity, k=43.315 with p=0.0185, and the primary morbidity, k=3.7171; p=0.0135. In a comparative analysis of the overall morbidity of patients with endemic goiter and other forms of non-toxic goiter among all age groups, the highest rates were found in adolescents (on average, 2041.78 cases per 100,000 population, k=-85.313), the lowest in children (on average, 468.71 cases per 100,000 population, k=-18.445), which is consistent with the indicators of primary morbidity (respectively, 684.11 cases per 100,000 population, k=-96.008 and 158.96 cases, k=-17.686).
The analysis of the dynamics of the overall incidence of congenital iodine deficiency syndrome conducted only in children 0-14 years old showed that there is a statistically significant decrease in the overall incidence since 2015 (k=-0.997, p = 0.0017), while the indicator of the primary incidence of goiter has only a slight, unreliable decrease (k=-0.0314, p = 0.6981). The average primary incidence of congenital iodine deficiency syndrome in the Voronezh Region is slightly lower than in the Russian Federation - 0.65 cases and 1 case per 100,000 population, respectively [5]. The tendency to reduce the incidence of congenital iodine deficiency syndrome indicates a positive effect of the regional measures for the prevention of iodine deficiency.

About the authors

Alexander Alexeevich Tcurkan

Voronezh State Medical University named after N.N. Burdenko
of the Ministry of Health of the Russian Federation
Department of Public Health and Health Care

Author for correspondence.
Email: alexandertsu@yandex.ru
ORCID iD: 0000-0003-1814-9260

student

Russian Federation, г.Воронеж ул. Студенческая д.10

References