Assessment of associations among urinary iodine concentration, iodized table salt and thyroid parameters during pregnancy in Algeria

doi:10.21203/rs.3.rs-5049853/v1

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Assessment of associations among urinary iodine concentration, iodized table salt and thyroid parameters during pregnancy in Algeria

https://doi.org/10.21203/rs.3.rs-5049853/v1

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Background and objectives: Iodine is a trace element whose adequate intakes are essential during pregnancy to promote the correct growth and development of the fetus. Iodine deficiency is the cause of several disorders associated with an increased risk of miscarriage or premature birth. The aim of this study was to assess the urinanry iodine concentration (UIC) and thyroid function of pregnant women (PW) in northern Algeria.

Methods: Healthy PW (n=173) were recruited from Gynecology-obstetrics service (Algiers) divided into three group. Spot urine and venous blood samples were collected to assess iodine status (urinary iodine concentration, serum thyroid hormones and anti-thyroid peroxidase antibodies concentrations. Correlation analysis was used to investigate the association between UIC and thyroid parameters.

Resultats: The median UIC values were 233 μg/L, 246.74 μg/L, 244.68 μg/L in the first, second and third trimester respectively. Median TSH and FT4 concentrations were within reference ranges during pregnancy. Among PW, 72.7%, 75.4% and 75.5% in the first, second and third trimester were TPO-Ab+. Among TPO-Ab+ PW in the first, second and third trimesters, 18.7%, 13% and 10.3% had subclinical hypothyroidism.

Conclusion: In northern Algeria, median UICs in PW indicate iodine sufficiency. About 75% of PW are TPO-Ab + and the frequency of undiagnosed SCH in pregnant women was the prevalence high. Monitoring of iodine fortification programs is vital to avoid both iodine deficiency and excess and raises an alarm of the potential risks of untreated thyroid disorder with an urgent need for a comprehensive national iodine status survey in Algeria.

thyroid

pregnant woman

UIC

subclinical hypothyroidism

iodized salt

Iodine is an essential micronutrient relatively abundant in the aquatic environment, the oceanic space constitutes the major reserve compartment of iodine with a content of 45–60 µg / L mainly in iodate and iodide form [1]. Iodine is also important for the synthesis of thyroid hormones wich are essential for the performance of many vital functions of the organism, such as regulation of basic metabolism, reproductive function including the development of the neurological system throughout pregnancy [2]. A normal adult in the reproductive age range requires about 150 µg of iodine per day; during pregnancy, this requirement rises to 200–250 µg [3]. Median urine iodine concentrations have been widely used as a biomarker of population iodine intake besides thyroglobulin [4, 5] with levels of UIC < 150µg/L considered low in pregnant women and > 500 µg/L considered excessive in pregnant women.

Iodine deficiency during pregnancy is the cause of several disorders including goitre characterized by an increase in the volume of the gland, disorders of reproduction as well as disorders in fetal development wich can lead to impaired fetal neurocognitive developmental defects such as cretenism (2,6). Therefore, an adequate iodine intake during pregnancy is essential for normal development of the fetus.

Iodine deficiency persists in some regions of Algeria, it has been previously, a significant goiter prevalence (30–70%) in the northern rural and mountain regions [7]. Even after the addition of iodized salt to food in 1990 (8), this is due to the fact that its iodine level cannot be analyzed regularly. According to WHO and al. [9], only 60.7% of households in Algeria use iodized salt with an inadequate intake of iodine (27µg /L); in 2016, a study conducting in the first trimester of pregnancy revealed a median of 180µg /L [10]; other studies, indcated a median of 227µg/L to a normal consumption of iodine [11]. In addition, no longitudinal study concerning the association between UIC and thyroid parameters during prenancy, has been conducted before in the country The purpose of our study is the assessment of the iodine status and the correlation between iodine nutrition and thyroid parameters during pregnancy as well as the analyze of potassium iodate contents in some salt consumed during pregnancy in coast sand rural regions in Algeria.

1. Subjects

This cross-sectional study enrolled 173 pregnant women who visited the Bologhine (Gynecology-obstetrics service, Public Hospital Etablishment Ibn Ziri, Algiers) with mea nage of 31,03 ± 0,38 years. Pregnant women were divided into three groups : 1st pregnancy (n = 22), 2nd trimester (n = 61) and 3rd trimester of preganccy (n = 90).

Pregnant women with known thyroid or other chronic diseases and those who had supplemented iodine during pregnancy were excluded from the study. Informed consent was obtained from all participants. The study was approved by EPH’s services in accordance with the MMA’s declaration of Helsinki on ethical principles for medical research involving humans (reference number: CEB001904). All women gave informed consent.

2. Methods

Spot urine samples were obtained in the morning and maintained frozen at − 20°C until analysis for UIC at the Human Nutrition Laboratory at the ETH Zürich, Switzerland, using a modified Sandell-Kolthoff method at 405 nm [12]. The WHO guidelines (median UIC: 150–249 µg/L among pregnant women) were utilized to determine iodine sufficiency [6]. Venous blood was collected from each pregnant women for the analyze of thyroid parametres and in the Laboratory of Analysis of Endocrinology, EPH Bologhine.

Radioimmunometric assays (IRMA) were used to analyze blood TSH and Tg. Commercial kits (IM3712, Immunotech Inc., Beckman Coulter, France; A85726, Cis Bio Bioassays, France) were used. The radioimmunologic method (RIA) was used to determine the serum FT4 and TPO-Ab concentrations. Commercial kits (IM1363, IM3321 for FT4 and A56719 for TPO-Ab assays, respectively, Immunotech Inc. Beckman Coulter, France) were utilized for this study.

Samples of the most used and table salts in Algeria were analyzed by the iodometric method published in the Official Journal of the People’s Democratic Republic of Algeria [13] on the requirement to use iodometric method for determination of iodine content in food salt. The dosage was carried out in the Physico-Chemical Laboratory (Saidal Pharmal Unit, Algeria). Potassium Iodate (KIO³) and Potassium Iodide (KI) are provided by Sigma Aldrich (Germany).

3. Statistical analysis

The experimental data were analyzed using Excel 2007 (Microsoft, Redmond, WA) and the R Project for Statistical Computing. The normality of the data distribution was tested using the Shapiro–Wilk test. Differences between groups of skewed variables were tested with Kruskal–Wallis one-way analysis of variance on ranks test and the strength of the association between two variables was determined using Spearman analysis. The level of significance was 0.05.

Statistical analysis was performed using the R Project for Statistical Computing. The Shapiro–Wilk test was used to detect a normal distribution data. Continuous variables were presented as mean ± standard deviation (SD) or median (interquartile range, IQR). The Kruskal-Wallis test were performed for comparisons of UIC and thyroid parameters between trimester. Spearman’s method was conducted for correlation analysis of UIC and other variables. The level of significance was P < 0.05.

Urinary iodine concentration (UIC) and potassium iodate (mg/kg) content in table salts marketed in Algeria

Adequate iodine intake (150–249µg/L) was found durnig pregnancy (232.6µg/L) with 27, 36 and 32% of PW during the first, second and third trimesters of pregnancy respectively (Fig. 1).

The population of pregnant women shows variations in ioduria with a gradual decrease during the three trimesters with median UIC values of 246.74 µg/L, 244.68 µg/L and 220,63 µg/L respectively. The proportions of PW with UIC values below 150µg/L were 23, 15 and 24% respectively for the three trimester of pregnancy. Pregnant women who consumed more than the recommended amount of iodine (250–499 µg/L) were likely to have higher proportions (> 40% per trimester), whereas 4% of PW had excessive UIC values (> 500 µg/L).

Analysis of the potassium iodate content was carried out on 11 samples of table salt marketed in Algeria, showed that only 42% were samples analyzed respected the Algerian recommendation regarding iodine content in table salts (50.55–84.25 mg/k of salt) for the prevention of iodine deficiency disorders (TDCI) compulsory by an executive decree. The amount of potassium iodate in salt must be for: Potassium iodate (67.40 mg/kg) of 50.55 mg/kg < 67.40 mg/kg < 84.25mg/kg (Fig. 2).

Our results showed that only 76%, 78% and 80% respectively of pregnant women with normal UIC consumed sufficiently iodized salt, 17%, 12% and 15% respectively of pregnant women consumed low-iodine salt wich represent 50% from analyzed samples, Only 7%, 8% and 5% of pregnant women respectively in 1st, 2nd and the 3rd trimester of pregnancy, consumed iodized salt whose potassium iodate analysis had indicated a higher potassium iodate level than required.

Assessment of associations among different parameters (UIC and thyroid parameters)

Pregnancy is associated with a decrease in the mean serum values of FT4 (Fig. 3) (Table 1). It was estimated to 15,21 ± 0,62 pmoles/L in the first trimester 14,14 ± 0,38 pmoles/L in the second trimester and 12,82 ± 0,24 pmoles/L during the third trimester of pergancy.

Table 1

thyroid parameters in pregnant women from Algiers.
	1st T n = 22	2nd T n = 61	3rd T n = 90	Comparing the group means	p values
FT4 (pmol/L)	15,21 ± 0,62	14,14 ± 0,38	12,82 ± 0,24	1st T/2nd T 2nd T/3rd T 1st T/3rd T	0,07 0,345 0,00095***
TSH (mUI/L)	1,65 ± 0,32	1,79 ± 0,15	1,88 ± 0,14	1st T/2nd T 2nd T/3rd T 1st T/3rd T	0,27 0,87 0,048
AC anti-TPO (U/mL)	25,96 ± 8,52	21,61 ± 3,91	38,25 ± 14,56	1st T/2nd T 2nd T/3rd T 1st T/3rd T	0,829 0,999 0,0038**

There is a statistically significant difference (p < 0,001) between the first and third trimesters of pregnancy. TSH averages, on the other hand, rise throughout pregnancy (Fig. 4) (Table I). It was estimated to 1,65 ± 0,32mUI/L in the first trimester, 1,79 ± 0,15mUI/L in the second trimester and 1,88 ± 0,14mUI/L during the the third trimester of pergancy. No statistical difference has beeen observed between differents groups.

Thyroglobulin is considered to be a biomarker of iodine deficiency, serum Tg levels are included in the norms and show no statistically significant differences from each other (Fig. 5) (Table I). Anti-TPO antibody frequencies were greater in the second trimester (75.4%) and the third trimester of pregnancy (75.5%) than the first trimester of pregnancy (72.7%) with no statistically significant difference between the trimester.

In the PW with positifs anti-TPO antibody, there is a negative correlation between the TSH levels with FT4 (r = − 0,101 ; p = 0,690) and UIC (r = − 0,277 ; p = 0,266). A significant positive correlation is also noted in the first trimester of pregnancy between anti-TPO antibody titers and circulating TSH levels (r = 0,586 ; p = 0,011).

In the second trimester, a statistically significant and positively correlated association appears between the UIC and the WP in the second trimester (r = 0,309 ; p = 0,037). The circulation levels of Tg and FT4 show a strong positive correlation (r = 0,429 ; p = 0,003).

Linear regression analysis conducted in the third trimester revealed an important negative association between urine iodine concentrations and levels of anti-TPO antibodies (r= -0,247 ; p = 0,042) and a significant positive correlation between serum Tg values and WP (r = 0,243 ; p = 0,046). Conversely, a highly significant negative association is observed between the serum concentrations of Tg and anti-TPO antibodies (r= -0,460 ; p = 7,96 10^− 5).

In our staudy, the median values of the UIC in pregnant women indicate optimal iodine intakes during all the pregnancy with the proportions with adequate iodine intake (150–249 µg/L) of 27, 36 and 32% during the pregancy and 76%, 78% and 80% respectively of pregnant women consumed sufficiently iodized salt. A median of 150–249 µg/L is recommended as an indication of sufficient iodine intake during pregnancy [9]. Several study reporeted a decline in UIC in pregnancy [13–15].

In our study, 23, 15 and 24% of PW had UIC values under 150 µg/L while 41, 43 and 40% had more than adequate iodine intake respectively for the three trimesters.

This decrease may indicate that iodine storage has been depleted as a result of renal excretion, nutritional insufficiency, or consumption by the maternal-fetal or to meet the increase in thyroid hormone requirement induced by pregnancy [16, 17]. The decrease in iodine concentration under 150 µg/L, may be explained by the difference in salt quality and ptassium iodine content consumed by pregnant women and that potassium iodine content in table salt, presents differences between the samples analysed additionally, due to the population's fish-eating habits and considering that Algeria's coastal sand rural areas are relatively proximity to the sea [16] and because iodine status has been irregularly monitored.

Beside UIC, that 90% of ingested iodine is excreted in the urine, a various others indicators which are used in monitoring and evaluating IDD control programmes, such as thyroid volume, hormone (TSH, T4) and thyroglobulin (Tg) [4, 5]. According to Glinoer [18] and Zimmermann [19], there is an increase in renal iodine excretion during the early stages of pregnancy due to the higher iodine needs, which as shown in our study results to an increase in maternal T4 production to ensure a transfer of thyroid hormones to the fetus and maintain a state of maternal euthyroidism, during which the fetal thyroid gland is not yet functional.

Level of FT4 decrease between the first and second trimester. A similar decrease has been reported by other studies [20, 21]. In order to maintain adequate maternal levels of free T4 and T3, the production of thyroids hormones increases by about 50% during pregnancy. The decrease in circulating FT4 levels in pregnant women in our study could be explained by the fact that the fetal thyroid gland is not functionally mature before the 18th-20th week of pregnancy. T4 is the main thyroid hormone transferred through the placenta. On the other hand, increased estrogen concentrations during pregnancy induce an increase in hepatic synthesis and sialylation of TBG, Thus decreasing its metabolic clearance. This results in a double increase in serum TBG and total T4 and T3, resulting in a transient decrease in free serum T4 and T3 throughout pregnancy. Thus, free T4 concentrations remain normal or decrease slightly [22].

In addition, during pregnancy the activity of placental desiodinase D3 is increased to regulate the levels of fetal blood in active hormones and recycle iodine. On the other hand, hCG would have a stimulatory effect on the transfer of iodine through the placenta (cytotrophoblastic cells) from the mother to the fetal compartment, notably by a transcriptional and translational effect of the sodium-iodide carrier gene (NIS) at the placental level [23].

Insufficient iodine intake leads to a shift towards increased preferential thyroid production of T3 and reduced production of T4 in order to save iodine. This can lead to low levels of T4 and FT4, while TSH concentrations are maintained in normal values due to the persistent negative feedback of T3. This adaptation can be beneficial for the mother, however, since T4 is the main thyroid hormone that crosses the placenta, Maternal HT supply to the fetus may be compromised [24]. Several studies have described the consequences of maternal iodine deficiency and maternal thyroid dysfunction in both mother and fetus [25]. Therefore, iodine supplementation is necessary during pregnancy to provide a supply for the mother and fetus [24].

In our study, the mean serum TSH concentration of pregnant women increased gradually from the first to the third trimester, with a significant difference between (p = 0.048).

Lower serum TSH levels in the first trimester could be explained by the high level of chorionic gonadotropin (hCG) secreted by syncytiotrophoblasts cells, which stimulates the corpus luteum to produce progesterone, essential for maintaining pregnancy. hCG is structurally similar to TSH and also has thyrotropic effects, leading to an increase in the first trimester of FT4 and FT3 and a concomitant suppression of circulating TSH. It has been suggested that such a mechanism of regulation of the foetus-maternal endocrine system allows, in early pregnancy, to have adequate concentrations of thyroid hormones necessary for fetal development since its thyroid gland still does not have the ability to synthesize its own hormones thyroid [18].

Our study showed normal serum Tg levels. However, studies reporting the relationship between serum Tg levels and iodine intakes in pregnant women are rare and no international reference is available. The few published data suggest that Tg could be slightly elevated during pregnancy in iodine-deficient pregnant women due to increased thyroid activity [27].

In our study, the proportions of positive anti-TPO antibody titers were during pregnancy with high averages over the three trimesters. Autoimmune thyroid diseases usually regress during pregnancy due to pregnancy-induced immunosuppression [28, 29]. Mechanisms that trigger the development of abnormal immune response and the relationship of self-related thyroid diseases-immune with excess iodine are still poorly understood and that an increase in thyroglobulin (Tg) iodization increases its immunogenicity and promotes oxidative damage [30–32].

The study of linear regression in the presence of anti-TPO antibodies showed a significant correlation between TSH levels and positive antibody titersTPO in the first trimester of pregnancy. This result is in agreement with the fact that the presence of high titres in anti- andTPO would be a predictor of subclinical hypothyroidism in pregnant women revealed by serum levels of TSH [33].

In the second trimester, a very significant positive correlation was found between the weeks of pregnancy and UIC due to increased glomerular filtration during pregnancy [34, 35]. A very significant correlation is also observed between the levels of FT4 and thyroglobulin. This association could be a reflection of an increased activity of the maternal thyroid gland to meet the needs of the fetus whose thyroid gland is non-functional before the 20th week of pregnancy [36].

During the third trimester, the weeks of pregnancy are positively correlated with serum thyroglobulin levels. According to Glinoer et al. [37], high serum thyroglobulin concentrations reflect a change in the anatomical structure of the thyroid and would be a marker for increased thyroid volume. Thyroglobulin elevation during the third trimester of pregnancy is also observed in other studies [38, 39]. Although thyroglobulin is an indicator of iodine deficiency and excess in a population [40], these results suggest that the increase in serum Tg concentration during pregnancy is mainly caused by increased thyroid secretion due to increased thyroid activity independently of iodine deficiency [18, 41].

The analysis of our results for pregnant women in the 3rd trimester of their pregnancy showed that circulating levels of Tg are strongly correlated with anti-TPO antibody titers (p = 7.96 10^− 5) due to the fact that the majority of pregnant women were in euthyroidism and positive for TPO-anti antibodies indicating an auto-thyroid diseaseimmune, probably in the process of installation, with a high predisposition to functional alterations of the gland during pregnancy or postpartum [42, 43].

Analysis of the potassium iodate content of table salt marketed in Algeria, showed that only 42% were samples analyzed respected the Algerian recommendation regarding iodine content in table salts (50.55–84.25 mg/k of salt) for the prevention of iodine deficiency disorders (TDCI) compulsory by an executive decree [44].

More than 70% of pregnant women with normal UIC, consumed sufficiently iodized salt, and less than 58% of the products marketed in Algeria does respect the recommendation of the Algerian regulations [44]. Our findings are similar to Guerras' [45] findings, which indicate that only 17,65% of the samples collected throughout the country conformed to the requirements established forth in the decree, compared to 57.35% and 11.76%, respectively, for samples with low contents (< 50.55 mg KIO³/kg) and elevated contents (> 84.25 mg KIO³/kg). Iodization in the Algiers region was found to be more adequate than in the regions of Batna, Biskra, M'sila, and Bordj Bou Arreridj, according to a comparison of iodine levels in samples obtained from these regions. This might be the result of the way salt is stored to prevent iodization, how salt is sold retail, and the sort of packaging that the salt is packaged in to influence its iodine level. It would appear that this deficiency still persists in both mountainous and coastal regions since 17%, 12% and 15% respectively of pregnant women consumed low-iodine salt..

In conclusion, the main objective of the study was to evaluate the iodine status and analyze the relationship between iodine nutrition and thyroid parameters during pregnancy. Additionally, we assessed the potassium iodate content in specific salt that pregnant women in Algeria's coastal and rural areas consumed. More than UIC 40% of pregnant had more than adequate iodine intake duruing pregnancy with normal thyroid function in Algiers. Linear regression analysis conducted in pregnant women, showed an association betwen UIC and thyroid parameters. In Algeria, the use of salt iodine supplements appears to have been successful in reducing iodine deficient disorders over the past decade. Nevertheless, iodine excess, brought on by exposure to the environment and/or eating foods high in this vitamin, is currently more common than iodine deficiency and is what causes thyroid disorders in both the mother and the fetus. In order to assess iodine intakes and improve the efficacy of iodine prophylaxis, it would be important to measure the amount of iodine consumed and to regularly perform national surveys.

Acknowledgements

We thank the health professionals at the Public Hospital Establishment Ibn Ziri in Bologhine, Algiers, who recruited subjects for this study, as well as the staff of Laboratory BPO/Endocrinology of the Faculty of Biological Sciences, USTHB, and the Endocrinology Department, Hôpital Bologhine, Algeria. We also want to thank Christophe Zeder from the ETH Zurich Human Nutrition Laboratory in Switzerland. Every author helped evaluate the results and write the manuscript.

Author contributions

Participated in research design : Z Hamouli-Said, MB Zimermann and A Kamel.

Performed and conducted experiments : Z Hamouli-Said, H Kherrab and L Lakabi.

Performed data analysis : MB Zimmermann.

Final approved of the version to be published : Z Hamouli-Said and MB Zimermann.

Funding

This study was supported by funding from the Ministry of Health for the Public Hospital Establishment Ibn Ziri, Bologhine, Algiers and the Ministry of Higher Education and Scientific Research for the Laboratory BPO/ Section Endocrinology of the Faculty of Biological Sciences, USTHB (16/2021-D/SB), Algeria.

Ethical approval

We used data and samples from women approved by EPH's services in accordance with the MMA's Declaration of Helsinki on ethical principles for human-centered medical research (reference number: CEB001904). All participants provided informed consent before being included in these studies (see "Methods").

Conflicts of Interest

The authors declare that they have no conflicts of interest.

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No competing interests reported.

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Assessment of associations among urinary iodine concentration, iodized table salt and thyroid parameters during pregnancy in Algeria

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Abstract

Figures

Introduction

Subjects and methods

1. Subjects

2. Methods

3. Statistical analysis

Results

Urinary iodine concentration (UIC) and potassium iodate (mg/kg) content in table salts marketed in Algeria

Assessment of associations among different parameters (UIC and thyroid parameters)

Discussion

Conclusuion

Declarations

References

Additional Declarations

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