Urinary Iodine in School Children and Pregnant Women of Trujillo State, Venezuela

Transcription

1 Urinary Iodine in School Children and Pregnant Women of Trujillo State, Venezuela Caballero Luis (*) (*) Physician responsible for the Coordination of the Iodine Deficiency Disorders Control Program. Instituto Nacional de Nutrición, Health Public Division. Caracas, Venezuela. ABSTRACT The main role of iodine is the synthesis of thyroid hormone. Thyroid hormones are related to brain development and metabolic regulation. Urinary iodine excretion is a useful and important indicator of the iodine status of a population. The World Health Organization (WHO) recommends that the median urinary iodine concentration (UIC) in a population of pregnant women should range between 150 and 249 µg/l and in a population of school children it should range between 100 and 200 µg/l. Objective: To determine the prevalence of iodine deficiency in school children and pregnant women of Trujillo State, in the Andean region of Venezuela. Material and Methods: Cross-sectional survey of 400 school children aged 7-14 years and 300 pregnant women. Casual urine samples were collected and analyzed for urinary iodine by Sandell-Kolthoff reaction. The criteria suggested by WHO to indicate iodine deficiency were applied. Results: Median urinary iodine for school children was 175 µg/l; and 6,25 % of children had urinary iodine concentrations below 50 µg/l. Median urinary iodine for pregnant women was 228 µg/l; and 25 % of pregnant women had urinary iodine concentrations below 150 µg/l. Conclusions: On the basis of the WHO criteria, iodine intake in school children and pregnant women in Trujillo State, Venezuela, is adequate. No financial conflicts of interest exist. Key words: iodine deficiency, urinary iodine, school children, pregnant women INTRODUCTION Iodine is an essential oligoelement in the synthesis of thyroid hormones, triiodothyronine (T 3 ) and thyroxin (T 4 ). An iodine-deficient diet is associated with a wide range of diseases, known as Iodine Deficiency Disorders (IDD) (1). Adverse effects of IDD include goiter, less physical strength, growth retardation and economic stagnation. The most devastating effects occur in the development of the human brain, and include mental retardation, cretinism, deaf mutism, squint, spastic diplegia and dwarfism (2). In the early 20th Century, almost all the countries of the Americas had severe iodine deficiency. The different governments and agencies made important efforts, especially in the 1990 s, to eliminate iodine deficiency in the population, by means of an aggressive campaign to promote the use of iodized salt (3). In the recent past, IDD have been recognized as a public health issue in the Andean region of Venezuela (4). Iodine deficiency has been corrected in Venezuela by means of a broad program focused on salt iodization and including research, monitoring, control and oversight, communication and education activities (5,6).

2 Adequate iodine nutrition in a population is evaluated by the measuring the urinary iodine concentration (IUC), in a representative sample of school-age children. The WHO recommends a median IUC equal to or above 100 µg/l, with less than 20% of individual samples with levels below 50 µg/l, as indicative of an adequate iodine nutrition in the population (7). An adequate iodine intake is essential for normal thyroid function. This is particularly important during pregnancy, when iodine requirements increase due to an increased renal clearance of iodine, the transfer of iodine from mother to fetus, as well as the increased need for iodine to produce more thyroid hormones and meet the high metabolic demands of pregnancy (8). Urinary iodine monitoring in school-age children of the Andean region has shown an increase in the median from 133 µg/l in to 187 µg/l in During this same time interval, the proportion of samples with a IUC below 50 µg/l decreased from 16.5 % to 2.4% (5). Based on the above, where monitoring has shown iodine adequacy in school-age children of Trujillo state, and there being no previous studies on the iodine levels in pregnant women, we decided to determine the median urinary iodine concentration in this population in order to implement the relevant recommendations. MATERIAL AND METHODS Cross-sectional study conducted during 2007 in Trujillo state, Andean region of Venezuela, in children aged 7-14 years, of both genders and living in 10 randomly selected districts, following WHO recommendations (7). We randomly selected 1-2 schools in each district. In each district, 40 school children were systematically selected for casual urine sample collection. During 2008, 10 districts were randomly selected among those were iodine urine had been previously monitored in school children in the state of Trujillo. In each district, 1-2 healthcare centers were randomly selected and 30 pregnant women were recruited (10 for each trimester) who presented at those centers and who had been lived in the Andean region at least within the previous 12 months. A questionnaire was administered to each pregnant woman and casual urine samples were collected from each of them, after obtaining their written informed consent. Gestational age was obtained by date of last menses and ultrasound findings, confirmed by the treating physician on the medical record. Pregnant women with a history of some conditions such as diabetes, heart disease, kidney disease or thyroid conditions were excluded. Urine samples collected were refrigerated until analysis at the laboratory for measurement of iodine concentration by the Sandell-Kolthoff reaction (9, 10). Results were expressed as micrograms of iodine per liter. Data analysis for the evaluation of iodine nutritional status in school-aged children and pregnant women was performed in accordance with the WHO criteria (7, 11, 12). Epidemiological criteria for measurement of the nutritional status of iodine in schoolaged children, based on the median IUC, consider iodine intake as normal when the median ranges between 100 and 200 µg/l (Table I). In addition, it is considered that no more than 20% of the population should have IUC values below 50 µg/l. For pregnant women, median IUCs of µg/ml represent adequate iodine intake (Table II). Data processing was performed using the Epi Info software version 6.0.

3 The conduction of the study was approved by the Ministry of Health and the National Institution of Nutrition. Study purposes were discussed with pregnant women, school children and educators. RESULTS In this study, casual urine samples were collected from 400 school children. The median urinary iodine excretion was 166 µg/l; only 6.25 % of children had IUC levels below 50 µg/l and 8.75 % had IUC levels above 300 µg/l. Median values in school-aged children of the 10 districts studied ranged between 108 and 260 µg/l and their distribution is shown in Table III. In pregnant women, 300 casual urine samples were collected, 100 for each trimester of pregnancy. The median urinary iodine excretion was 228 µg/l; 25% of pregnant women had IUC below 150 µg/l (Table IV). Median values in pregnant women of the 10 districts studied ranged between µg/l and µg/l and their distribution is shown in Table V. The median IUCs for the first, second and third trimester of pregnancy was µg/l, µg/l and µg/l, respectively (Figure 1). TABLE I. Epidemiological criteria for measurement of the nutritional status of iodine in schoolaged children based on the median iodine urinary concentration. Median Value µg/l Iodine status <20 Severe iodine deficiency Moderate iodine deficiency Mild iodine deficiency Normal iodine intake More than adequate iodine intake >300 Excessive iodine intake TABLE II. Criteria for categorizing iodine intake in pregnant women based on the median iodine urinary concentration Median Value µg/l <150 Insufficient Adequate Category of Iodine Intake More than adequate >500 Excessive

4 TABLE III. Iodine urinary concentration monitoring in school children from ten districts in the state of Trujillo. Year District Median µgl/l <50 µgl/l % >300 µgl/l % Monte Carmelo Boconó Bolívar Candelaria Carache San Rafael de Carvajal Escuque Andrés Bello Pampán Campo Elías TABLE IV. Distribution of iodine urinary concentration levels in pregnant women in the state of Trujillo. Year Median IUC ranges Pregnant women No. % Inadequate (>150 µgl/l) Adequate ( µgl/l) More than adequate ( µgl/l) Excessive (>500 µgl/l) Total TABLE V. Median iodine urinary concentration per district in pregnant women of the state of Trujillo. Year District Median (µgl/l) Boconó Urdaneta Carache 261 Trujillo 206 Pampán Valera 200 Escuque Pampanito 260 Bolívar 195 Monte Carmelo 189.5

5 First Second trimester Third Figure 1. Medina iodine urinary concentration per trimester of pregnancy, state of Trujillo. Year DISCUSSION In this study, casual urine samples were refrigerated until assayed because 24-hour samples are difficult to obtain for population-based studies (13). Median IUC in school-aged children is recommended for the evaluation of iodine nutrition in the population (7). When median IUC was adequate in school-aged children, it was usually assumed that iodine intake was also adequate in the rest of the population, including the group of pregnant women. However, in several countries and regions, previously considered to have an optimal iodine nutrition based on previous iodine urinary concentration studies in school children, low iodine urinary concentrations have been reported in pregnant women (14-17). It is known that in pregnant women dietary iodine requirements are approximately 70 µg per day higher than in non-pregnant women. For this reason, the WHO currently recommends a median IUC of µg/l in pregnant women as indicative of an adequate iodine intake. This indicator should not be used for the purposes of individual diagnosis and treatment, and it results from a recent WHO technical consultation (11, 18). In Venezuela, unlike in many European countries, the use of iodized salt is compulsory in the food industry (19), therefore, foods processed in this country would supply an amount of iodine in the diet that has not been assessed yet. Consumption of some processed foods may be determinant in iodine dietary supply, such is the case of bread, which has brought about a significant increase in iodine intake in Chile (20), also reported in the province of Santiago del Estero in Argentina (21). Both agricultural practices and their geographical location have a variable impact on the iodine content of foods. Thus, in Peru, cow s milk from Coastal areas had six-fold higher iodine content than cow s milk from mountain ranges (22). It has been reported that the percentage of women of child-bearing potential with excessive IUC (>300 µg/l) could not be accounted for on the basis of salt intake only with a iodine average of 31.7 ppm.; which could be related to a more diverse diet, including processed foods to which iodized salt was added or which were fortified with iodine-containing mixtures of micronutrients (23). The above could partly account for the findings in school-aged children, who showed a normal iodine intake in all 10 districts of the state of Trujillo where IUC was monitored, in spite of the fact that only 55% of 1000 salt samples from monitoring of household

6 salt consumption were adequately iodized ( 15 ppm) and the average content of 36 ppm of iodine was found in 30 salt samples collected throughout 2007 from retail stores in the capital city of the state of Trujillo. Pregnant women living in this geographical area far from the sea might be benefiting from the growing consumption of processed foods as sources of iodine, such as sea fish, and from iodine supplied in some vitamin and mineral supplements recently available on the local market. Of all pregnant women surveyed, 70% and 59% reported a frequent consumption (once-twice a week or more frequently) of canned tuna and canned sardine, respectively. Adequate iodine nutrition was found in pregnant women from 9 of the 10 districts studied; in Pampán, where the median IUC of pregnant women was low (137.5 µg/l), household consumption of adequately iodized salt had been very low (37%) the previous year. Salt processing should be more closely monitored and controlled in order to obtain an adequately iodized product in a sustained manner (24). Furthermore, especially in pregnant women, other factors should be considered, such as poverty status and educational level, which might limit access to a diversified intake including iodine-rich foods and the few multivitamin and mineral supplements available that are sources of iodine (25, 26), as pregnant women from low socioeconomic status tend to consume products which are rich in calories, poor in proteins and with a low content of vitamins and micronutrients, which are relatively economical (27). In 66% of the households of the pregnant women studied, over 30% of the monthly family income was assigned to the purchase of food. This, added to the fact that only 18.67% of pregnant women completed their basic education, may lead to an impaired quality of life for these women and their offspring. Goiter determination was not considered in school-aged children and pregnant women participating in this study. The most recent data on goiter prevalence in children from Trujillo, obtained by clinical examination and ultrasound were obtained from the Mobile Thyroid Project (Proyecto Tiroides Móvil) (5) conducted in 1999, differently from, for example, the large-scale monitoring of endemic goiter conducted in Argentina, which was very well reported by Salvaneschi and García (28). Contrary to what might be expected, the overall median IUC in pregnant women was 23% higher than that of school children from the same region. These findings should encourage further research in order to quantify iodine supply from other sources different from table salt, such as pharmacological supplements or other foods. However, the fact that 25% of individual urine samples had a iodine concentration <150 µg/l leads as to wonder if, despite a normal median, a high proportion of low individual values would represent a risk for iodine deficiency in pregnant women. CONCLUSION Based on iodine urinary excretion, the best biochemical marker of iodine status in the population, we conclude that school-aged children and pregnant women in the state of Trujillo, Venezuela, have adequate iodine nutrition. Acknowledgements: We would like to thank Teodosio Avendaño for his valuable support to this research, the school children and their parents and educators; pregnant women, nurses, food administrators, nutritionists and prenatal care physicians, and the regional heath, nutrition and education authorities, who permitted the conduction of this research, financially supported by the National Institute of Nutrition.

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