Iodine nutrition status in Spain Needs for the future. / La nutrición de yodo en España. Necesidades para el futuro.

Although iodine nutrition in Spain has improved in recent years, the problem is not completely resolved. It is necessary that health institutions establish measures to ensure an adequate iodine nutrition of the population, especially among the highest risk groups (children and adolescents, women of childbearing age, pregnant women and nursing mothers). A low salt intake should be advised, but it should be iodized. It is also imperative that food control agencies establish effective control over adequate iodization of salt. Indicators on iodine nutrition should be included in future health surveys. The EUthyroid study and the Krakow Declaration on iodine nutrition provide an opportunity to set up a pan-European plan for the prevention of iodine deficiency that should be considered and used by health authorities.

Evolution of urinary iodine excretion over eleven years in an adult population.

BACKGROUND & AIMS: Few prospective cohort studies have evaluated dietary iodine intake and urinary iodine concentrations in the general adult population. We assess the evolution of urinary iodine excretion and factors that may influence it in an adult population followed for 11 years. METHODS: A population-based cohort study was undertaken in Pizarra (Spain). In the three study phases (baseline (n = 886), and 6 (n = 788) and 11 years later (n = 501)), participants underwent an interview and a standardized clinical examination that included a food questionnaire, and thyroid hormone and urinary iodine determinations. Subjects with thyroid dysfunction, palpable goiter or urinary iodine excretion >400 µg/L were excluded. RESULTS: Urinary iodine increased over the years (100.6 ± 70.0 µg/L at baseline vs. 125.4 ± 95.2 µg/L at 6 years and 141.6 ± 81.4 µg/L at 11 years; p < 0.0001). Urinary iodine was significantly higher in subjects who reported iodized salt consumption and in subjects with a higher intake of dairy products (p < 0.05). Consumption of iodized salt (Risk ratio (RR) = 1.23, 95% CI [1.01-2.05]) and dairy products (RR = 2.07, 95% CI [1.01-4.23]), and a baseline urinary iodine concentration ≥100 µg/L (RR = 1.26, 95% CI [1.04-1.53]) were significantly associated with urinary iodine concentrations ≥100 µg/L at 11 years. There is no correlation between thyroid function (TSH, free triiodothyronine or free thyroxine levels) and urinary iodine concentrations in conditions of iodine sufficiency. CONCLUSIONS: The increase in urinary iodine concentrations over eleven years is associated with an increase in iodized salt intake and with the dairy products intake, and possibly with a higher iodine content of dairy products. However, individual variability in urinary iodine excretion was not fully explained by dietary iodine intake alone; previous urinary iodine concentrations were also important.

Maternal-fetal thyroid function at the time of birth and its relation with iodine intake.

BACKGROUND: The effects of moderate variations in dietary iodine intake on maternal and fetal thyroid function are poorly understood. Recent studies question the usefulness of neonatal screening of congenital hypothyroidism as a tool for monitoring iodine deficiency. We proposed to test the hypothesis of an association between iodine intake during the last trimester of pregnancy and fetal thyroid function at the time of birth. METHODS: The study was undertaken at term in 233 healthy pregnant women (29.7±5.6 years) and in their newborn. Inclusion of women in the study was done within the 24 hours before delivery. RESULTS: The median maternal urinary iodine concentration was 126.5 µg/L. The maternal free triiodothyronine (FT3), although not thyrotropin (TSH) and free thyroxine (FT4), correlated significantly with the urinary iodine concentration (r=0.17, p=0.013). The cord blood TSH, FT4, and FT3 correlated positively with the maternal urinary iodine concentration at the time of delivery (r=0.24, p=0.001; r=0.16, p=0.032; and r=0.24, p=0.003, respectively). The cord blood and heel blood TSH correlated positively with the amniotic fluid iodine concentration (r=0.21, p=0.015 and r=0.15, p=0.036). The cord blood TSH correlated positively with the cord blood FT4 (r=0.21, p=0.022) and FT3 (r=0.32, p=0.017). The maternal TSH correlated significantly with the cord blood TSH (r=0.22, p=0.014) and with the heel blood TSH (r=0.13, p=0.050). CONCLUSIONS: The results of this study show the presence of a positive association of TSH-FT4 at the time of delivery, which may be modulated by the amount of iodine consumed by the mother during pregnancy.

Infant neurocognitive development is independent of the use of iodised salt or iodine supplements given during pregnancy.

The benefits of iodine supplements during pregnancy remain controversial in areas with a mild-to-moderate iodine deficiency. The aim of the present study was to determine the effect of improving iodine intakes, with iodised salt (IS) or iodine supplements, in pregnant Spanish women. A total of 131 pregnant women in their first trimester were randomly assigned to three groups: (1) IS in cooking and at the table, (2) 200 µg potassium iodide (KI)/d or (3) 300 µg KI/d. No differences were found in thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3) or thyroid volume (TV) between the three groups. Regardless of the group in which women were included, those who had been taking IS for at least 1 year before becoming pregnant had a significantly lower TV in the third trimester (P= 0.01) and a significantly higher urinary iodine in the first (173.7 (sd 81.8) v. 113.8 (sd 79.6) µg/l, P= 0.001) and third trimesters (206.3 (sd 91.2) v. 160.4 (sd 87.7) µg/l, P= 0.03). Also, no differences were seen in TSH, FT4 or FT3. Children's neurological development was not significantly associated with the consumption of IS for at least 1 year before becoming pregnant and no differences were found according to the treatment group. In conclusion, in pregnant women with insufficient iodine intake, the intake of IS before becoming pregnant was associated with a better maternal thyroid function. The form of iodide intake was not associated with maternal thyroid function or children's neurological development.

[Reference values for thyroid hormones in the population of pregnant women in Jaen (Spain)]. / Valores de referencia de hormonas tiroideas en la población de mujeres gestantes de Jaén.

OBJECTIVE: To evaluate thyroid function in the three trimesters of pregnancy in healthy women taking iodine and to define the reference ranges of normality in this population. DESIGN: Descriptive study of pregnant women to define the ranges of normality of thyroid hormones in this population. SETTING: Jaen and Osuna (Spain). POPULATION: Healthy pregnant women. METHODS: Thyroid hormone determination in the three trimesters of pregnancy in healthy women taking iodine supplements. RESULTS: A total of 429 pregnant women taking iodine supplements to maintain urinary iodine levels within the normal range were included. T4-l levels were between 0.60 and 1.06 in the first trimester, between 0.43 and 0.85 ng/dl in the second and between 0.40 and 0.82 ng/dl in the third. Thyroid stimulating hormone (TSH) reference values were between 0.23 and 4.18µUI/ml in the first trimester, 1.78 and 3.89µUI/ml in the second and 2.01 and 4.30µUI/ml in the third. T3-l values were between 2.33 and 3.84 pg/ml in the first trimester, between 2.04 and 3.51 pg/ml in the second and between 1.99 and 3.46 pg/ml in the third. CONCLUSION: Bearing the 3rd and 97th percentiles in mind, the reference ranges in our population were far below those recommended by our reference laboratory. In view of these results, these values should be redefined to avoid incorrect diagnoses of hyperthyroxinemia in healthy pregnant women.

Iodine intakes of 100-300 µg/d do not modify thyroid function and have modest anti-inflammatory effects.

Little information is available as to whether doses of iodide similar to those recommended in clinical practice for the prevention of iodine deficiency in pregnant women affect thyroid function. The aim of the present study was to analyse whether doses of iodide can affect thyroid function in adults, and evaluate its effect on plasma markers of oxidative stress, inflammation and acute-phase proteins. A total of thirty healthy volunteers (ten men and twenty women) with normal thyroid function were randomly assigned to three groups (n 10). Each group received a daily dose of 100, 200 or 300 µg of iodide in the form of KI for 6 months. Free tetraiodothyronine (FT4) levels at day 60 of the study were higher in the groups treated with 200 and 300 µg (P = 0·01), and correlated with the increase in urinary iodine (r 0·50, P = 0·007). This correlation lost its significance after adjustment for the baseline FT4. The baseline urinary iodine and FT4 correlated positively with the baseline glutathione peroxidase. On day 60, urinary iodine correlated with C-reactive protein (r 0·461, P = 0·018), and free triiodothyronine correlated with IL-6 (r - 0·429, P = 0·025). On day 60, the changes produced in urinary iodine correlated significantly with the changes produced in α1-antitrypsin (r 0·475, P = 0·014) and ceruloplasmin (r 0·599, P = 0·001). The changes in thyroid-stimulating hormone correlated significantly with the changes in α1-antitrypsin (r - 0·521, P = 0·005) and ceruloplasmin (r - 0·459, P = 0·016). In conclusion, the administration of an iodide supplement between 100 and 300 µg/d did not modify thyroid function in a population with adequate iodine intake. The results also showed a slight anti-inflammatory and antioxidative action of iodide.

Iodine concentration in cow's milk and its relation with urinary iodine concentrations in the population.

BACKGROUND & AIMS: The importance of milk intake to the supply of dietary iodine is not fully known. We therefore undertook a study in Spain of the iodine concentration in cow's milk and the impact of the frequency of milk consumption on urinary iodine concentrations in three study populations. METHODS: We studied the iodine concentration in 362 samples of milk from 45 commercial brands and compared it with the milk iodine status in studies undertaken 17 years earlier. The epidemiologic studies were performed in three different places in the south of Spain: two in school-age children (N = 757 and N = 1205 children) and one in adults (N = 1051). A milk consumption questionnaire was given and urinary iodine concentrations measured. RESULTS: The mean concentration of iodine in the milk rose from 1991 (117 ± 37 µg/L) to 2008 (259 ± 58 µg/L) (P < 0.001). The iodine concentration was greater in skimmed milk (273 ± 52 µg/L) than in semi-skimmed milk (254 ± 57 µg/L) or whole milk (251 ± 61 µg/L) (P < 0.0001). The winter samples had a greater concentration of iodine (270 ± 55 µg/L) than the summer samples (247 ± 58 µg/L) (P < 0.0001), independently of the type of milk. The urinary iodine concentrations in all three epidemiologic studies were significantly associated with the frequency of milk intake. CONCLUSIONS: The concentration of iodine in cow's milk has risen over recent years, and it is higher in skimmed milk. The results also show that cow's milk is a relevant source of dietary iodine.

Effect of iodine prophylaxis during pregnancy on neurocognitive development of children during the first two years of life.

CONTEXT: The association between thyroid function during pregnancy and the later mental and psychomotor development of the child is supported by numerous experimental, clinical, and epidemiological studies. OBJECTIVE: The aim of the study was to evaluate the psychological development of infants aged 3 to 18 months whose mothers had received 300 microg of potassium iodide during the first trimester of their pregnancy and compare with infants whose mothers had received no iodine supplements. DESIGN AND STUDY SUBJECTS: The study included 133 women who had received 300 microg of potassium iodine and 61 women who had received no iodine supplements. MAIN OUTCOME MEASURES: The neuropsychological status of the children was evaluated with the Bayley Scales of Infant Development, and measurements were made of TSH, free T(3), free T(4), and urinary iodine. RESULTS: Those children whose mothers had received an iodine supplement of 300 microg had a more favorable psychometric assessment than those of the other group of mothers. They had higher scores on the Psychomotor Development Index (P = 0.02) and the Behavior Rating Scale. CONCLUSIONS: Dietary iodine supplements not only have no harmful effect on the neurodevelopment of the children, they may even be beneficial. Given the possible presence of confounding variables not controlled for in this study, these findings should be considered as preliminary.

Amniotic fluid iodine concentrations do not vary in pregnant women with varying iodine intake.

Iodine deficiency is an important clinical and public health problem. Its prevention begins with an adequate intake of iodine during pregnancy. International agencies recommend at least 200 microg iodine per d for pregnant women. We assessed whether iodine concentrations in the amniotic fluid of healthy pregnant women are independent of iodine intake. This cross-sectional, non-interventional study included 365 consecutive women who underwent amniocentesis to determine the fetal karyotype. The amniocentesis was performed with abdominal antisepsis using chlorhexidine. The iodine concentration was measured in urine and amniotic fluid. The study variables were the intake of iodized salt and multivitamin supplements or the prescription of a KI supplement. The mean level of urinary iodine was 139.0 (SD 94.5) microg/l and of amniotic fluid 15.81 (SD 7.09) microg/l. The women who consumed iodized salt and those who took a KI supplement had significantly higher levels of urinary iodine than those who did not (P = 0.01 and P = 0.004, respectively). The urinary iodine levels were not significantly different in the women who took a multivitamin supplement compared with those who did not take this supplement, independently of iodine concentration or multivitamin supplement. The concentrations of iodine in the amniotic fluid were similar, independent of the dietary iodine intake. Urine and amniotic fluid iodine concentrations were weakly correlated, although the amniotic fluid values were no higher in those women taking a KI supplement. KI prescription at recommended doses increases the iodine levels in the mother without influencing the iodine levels in the amniotic fluid.