Effects of iodine supplementation during pregnancy on pregnant women and their offspring: a systematic review and meta-analysis of trials over the past 3 decades

OBJECTIVE

The current systematic review aimed to provide comprehensive data on the effects of iodine supplementation in pregnancy and investigate its potential benefits on infant growth parameters and neurocognitive development using meta-analysis.

METHODS

A systematic review was conducted on trials published from January 1989 to December 2019 by searching MEDLINE, Web of Science, the Cochrane Library, Scopus, and Google Scholar. For most maternal and neonatal outcomes, a narrative synthesis of the data was performed. For birth anthropometric measurements and infant neurocognitive outcomes, the pooled standardized mean differences (SMDs) with 95% CIs were estimated using fixed/random effect models.

RESULTS

Fourteen trials were eligible for inclusion in the systematic review, of which five trials were included in the meta-analysis. Although the findings of different thyroid parameters are inconclusive, more consistent evidence showed that iodine supplementation could prevent the increase in thyroglobulin concentration during pregnancy. In the meta-analysis, no differences were found in weight (-0.11 (95% CI: -0.23 to 0.01)), length (-0.06 (95% CI: -0.21 to 0.09)), and head circumference (0.26 (95% CI: -0.35 to 0.88)) at birth, or in cognitive (0.07 (95% CI: -0.07 to 0.20)), language (0.06 (95% CI: -0.22 to 0.35)), and motor (0.07 (95% CI: -0.06 to 0.21)) development during the first 2 years of life in infants between the iodine-supplemented and control groups.

CONCLUSION

Iodine supplementation during pregnancy can improve the iodine status in pregnant women and their offspring; however, according to our meta-analysis, there was no evidence of improved growth or neurodevelopmental outcomes in infants of iodine-supplemented mothers.

Iodine status and supplementation before, during, and after pregnancy

Iodine intake is essential for the production of thyroid hormone. Iodine deficiency remains a public health problem in many regions around the world. Iodine deficiency can present as a spectrum of disorders depending on the degree of severity. Pregnant and lactating women are particularly vulnerable to iodine deficiency disorders because of their increased iodine requirements. Severe maternal iodine deficiency has been associated with cretinism or impaired neurodevelopment in children as well as obstetric complications. Universal salt iodization has been shown to prevent these disorders in severely iodine deficient areas. Recently, observational studies have demonstrated an association between mild-to-moderate iodine deficiency and poorer cognitive outcomes in children. In this review, we describe the iodine requirements for pregnant and lactating women, how population iodine status can be assessed, the effects of maternal iodine deficiency and excess, and current data regarding efficacy of iodine supplementation for women who are pregnant or lactating.

WITHDRAWN: Iodine supplementation for preventing iodine deficiency disorders in children

BACKGROUND

Iodine deficiency is the main cause of potentially preventable mental retardation in childhood, as well as causing goitre and hypothyroidism in people of all ages. It is still prevalent in large parts of the world.

OBJECTIVES

To assess the effects of iodine supplementation overall, and of different forms and dosages of iodine supplementation separately, in the prevention of iodine deficiency disorders in children.

SEARCH METHODS

The Cochrane Library, MEDLINE, EMBASE and reference lists, databases of ongoing trials and the Internet were searched.

SELECTION CRITERIA

We included randomised controlled trials and prospective controlled trials not using randomisation of iodine supplementation in children living in areas of iodine deficiency.

DATA COLLECTION AND ANALYSIS

Two reviewers did the initial data selection and quality assessment of trials independently. As the studies identified were not sufficiently similar and not of sufficient quality, we did not do a meta-analysis but summarised the data in a narrative format.

MAIN RESULTS

Twenty-six prospective controlled trials were related to our question, assessing a total of 29613 children. Twenty of them were classified as being of low quality, six of moderate quality. Most studies used iodised oil as a supplement, but other supplements were also used. The intervention groups were compared to a non-supplemented control group, different doses or different forms of iodine supplementation.There was a clear tendency towards goitre reduction with iodine supplementation; this was significant in several studies. Significant differences in physical development were not seen, except in one study. Results for differences in cognitive and psychomotor measures were mixed, with only few studies showing a positive intervention effect. One study suggested that infant mortality was lowered after iodine supplementation.Most studies showed a significant increase in urinary iodine excretion and levels recommended by the WHO were reached in most cases after supplementation. Thyroid-stimulating hormone (TSH) levels were significantly reduced in one study. In 1.8% of the children investigated, adverse effects were found, most of them were minor and transient.

AUTHORS' CONCLUSIONS

Despite most of the included studies being of low quality, the results suggest that iodine supplementation, especially iodised oil, is an effective means of decreasing goitre rates and improving iodine status in children. Indications of positive effects on physical and mental development and mortality were seen, although results were not always significant. Adverse effects were generally minor and transient. Insufficient evidence was available on non-oil supplements. High quality controlled studies investigating relevant long term outcome measures are needed to address the question of the best form of iodine supplementation in different population groups and settings.

Iodine Deficiency: Consequences and Progress toward Elimination

While traditionally associated with cretinism and goiter, iodine deficiency has broad effects on central nervous system development that can occur in the absence of either condition. Any maternal iodine deficiency results in a range of intellectual, motor, and hearing deficits in offspring. This loss in intellectual capacity limits educational achievement of populations and the economic prowess of nations. Progress made since the historic World Summit for Children in 1990 has been outstanding. Approximately 70% of households in the world used iodized salt by 2000, compared with less than 20% in 1990. It is estimated that at least 85 million newborns out of 130 million annual births are protected from a loss in learning ability that would otherwise have occurred. The elimination of iodine deficiency, by expedient production, marketing, and universal consumption of iodized salt, represents a significant development effort in public nutrition. Although globally iodine nutrition has greatly improved, 20% to 30% of pregnancies and thus newborns still do not fully benefit from the use of iodized salt. Countries where success is in evidence could rapidly revert back to deficiency if vigilance is not maintained. Just as success came through concerted public-private-civic actions, making sure that this is expanded and will steadily go on requires continuous collaboration.

Protective effects of GM-CSF in experimental neonatal hypothyroidism

Hypothyroidism induced by methimazole (MMI), has a negative impact on the postnatal development. Neonatal Granulocyte Macrophage-Colony Stimulating Factor [GM-CSF; 50μg/kg, intramuscular injection at postnatal day (PND) 17] had been tested to ameliorate the effects of MMI [0.05%, (weight per volume; w/v), intraperitoneal injection at PND 15]-induced hypothyroidism in Wistar rats. The hypothyroid conditions due to the administration of MMI produced inhibitory effects on neonatal serum thyroxine (T4), 3,5,3'-triiodothyronine (T3), neutrophil count in bone marrow and blood, cerebellar glutathione (GSH) and acetylcholinesterase (AchE), although it induced stimulatory actions on serum thyrotropin (TSH), growth hormone (GH), insulin growth factor-II (IGF-II), tumor necrosis factor alpha (TNF-α), and cerebellar malondialdehyde (MDA) at PND 19. The treatment with GM-CSF could reverse the depressing and stimulating effects of MMI on these markers except for cerebellar AchE where its enhancement was non-significant (P>0.05) at tested PND. Thus, neonatal GM-CSF may be responsible for suppressing autoimmune responses and preventing hypothyroidism.

NEW BORN SCREENING IN PREVENTING CONGENITAL HYPOTHYROIDISM

Congenital Hypothyroidism is one of the most common preventable causes of mental retardation which is highly prevalent in our society due to lack of a national neonatal screening program, lack of education of the parents, increased consanguinity, and lack of suspicion from doctor's leads to delayed diagnosis and an increased incidence of congenital hypothyroidism in our society. This Menace can be easily tackled with a mass neonatal screening program and effective legislation which would make sure that serious efforts are being made to eradicate this preventable disease from Pakistan.

Thyroid disorders during pregnancy

Thyroid physiology is altered during pregnancy as a result of an increase in thyroid-binding globulin, the stimulatory effect of hCG on TSH receptors, and increased peripheral thyroid hormone requirements. In addition, hyper and hypothyroid disorders are prevalent among women of reproductive age, and most of them have a significant impact on the gravida, fetus and neonate. Aberrant thyroid function can be readily recognized and treated during pregnancy, avoiding such complications. Here, we will review the thyroid function changes occurring during pregnancy, the different disorders, their maternal and fetal implications, and the ways to screen, prevent and treat these conditions.

Teratology public affairs committee position paper: iodine deficiency in pregnancy

Iodine deficiency is an important nutritional deficiency, with more than 2 billion people worldwide estimated to be at risk. The developing fetus and young children are particularly at risk. During pregnancy and lactation, iodine requirements increase, whether in iodine-poor or iodine-sufficient countries, making the mother and the developing fetus vulnerable. The American Thyroid Association (ATA) recommends 250 micrograms per day of iodine intake for pregnant and lactating women. The thyroid gland is able to adapt to the changes associated with pregnancy as long as sufficient iodine is present. Dietary intake is the sole source of iodine, which is essential to the synthesis of thyroid hormones. Iodine is found in multiple dietary sources including iodized salt, dairy products, seaweed, and fish. Prenatal vitamins containing iodine are a good source of iodine, but iodine content in multivitamin supplements is highly variable. Congenital hypothyroidism is associated with cretinism. Clinical hypothyroidism has been associated with increased risk of poor perinatal outcome including prematurity, low birth weight, miscarriage, preeclampsia, fetal death, and impaired fetal neurocognitive development. Subclinical hypothyroidism is also associated with poor pregnancy outcomes and potential fetal neurocognitive deficits, but the data are more variable than those for clinical hypothyroidism. We concur with the ATA recommendation that all pregnant and lactating women should ingest (through diet and supplements) 250 micrograms of iodine daily. To achieve this goal, we recommend that all pregnant and lactating women take daily iodine supplementation of 150 micrograms.

Combating iodine deficiency disorders to achieve millennium development goal 4 in India: reduction in infant mortality rate

In severe iodine deficient areas, iodine deficiency has been documented to be an important etiological factor leading to poor fetal growth and development. Iodine is essential for physical growth and development of the central nervous system of the fetus. Iodine deficiency in pregnant mothers leads to increased incidence of infertility and abortions, perinatal mortality and infant child mortality. The clinical iodine supplementation trials have documented adverse health consequences due to iodine deficiency. Evidence from observational studies concludes that prevention of iodine deficiency can lead to reduction in infant mortality rate and facilitate to achieve millennium development goal-4.

Neurological damage to the fetus resulting from severe iodine deficiency during pregnancy

Endemic cretinism is characterised by multiple neurological defects including deaf-mutism, diplegia, squint, and mental deficiency. The condition is widely prevalent in the Highlands of New Guinea in association with severe iodine deficiency. Previous studies have shown that iodised oil provides a very satisfactory correction of severe iodine deficiency in New Guinea. A controlled trial on the use of intramuscular iodised oil in the prevention of endemic cretinism was carried out in the Western Highlands of New Guinea and involved a population of approximately 8000. Subsequent follow-up over four years revealed 26 endemic cretins out of a total of 534 children born to mothers who had not received iodised oil; the mothers of 5 of these cretins were pregnant at the start of the trial. In comparison, 7 cases of endemic cretinism occurred among 498 children born to mothers who had been treated with iodised oil; in 6 of these 7 cases, the mother was pregnant when the trial commenced. It is concluded that intramuscular iodised oil is effective in the prevention of endemic cretinism and that, for it to be effective, it should be given prior to conception. This suggests that severe iodine deficiency in the mother produces neurological damage during fetal development.

Early levothyroxine treatment on maternal subclinical hypothyroidism improves spatial learning of offspring in rats

Maternal hypothyroidism has adverse effects on neural development in the offspring. The present study aimed to investigate whether maternal subclinical hypothyroidism impairs spatial learning in the offspring, as well as the efficacy and optimal time of levothyroxine (L-T(4)) treatment in pregnancy. Female adult Wistar rats were randomly divided into six groups (n = 10 per group): control, hypothyroid (H), subclinical hypothyroid (SCH) and SCH treated with L-T(4), starting from the tenth, thirteenth and seventeenth gestational day (GD10, GD13 and GD17), respectively, to restore normal thyroid hormone levels. Spatial learning was assessed on progenies by a water maze test, a field excitatory postsynaptic potential (fEPSP) recording, and an long-term potentiation induction assay. Protein levels of early growth response protein 1 (Egr1), activity-regulated cytoskeleton-associated protein (Arc), Ras-proximate-1 (Rap1), p-extracellular signal-regulated kinase (p-ERK) and brain-derived neurotrophic factor (BDNF) were determined by western blotting. Progenies from the SCH and H groups demonstrated significantly longer mean latency in the water maze test and a lower amplification percentage of the amplitude and slope of the fEPSPs compared to offspring of the control group. L-T(4) treatment for the GD10 and GD13 groups significantly shortened mean latency and increased the amplification percentage of the amplitude and slope of the fEPSPs of the progeny of rats with subclinical hypothyroidism. However, L-T(4) treatment for the GD17 group showed only minimal effects on spatial learning in the offspring. Progenies of SCH and H groups had lower levels of Egr1, Arc, p-ERK and BDNF but higher levels of Rap1 compared to those of the controls. L-T(4) treatment ameliorated these protein expression changes in the progeny of rats with subclinical hypothyroidism. Maternal subclinical hypothyroidism impaired spatial learning in the offspring; L-T(4) treatment in early pregnancy recovered this adverse effect, and the optimal time of treatment should start from early pregnancy (GD10 and GD13).

[Thyroid dysfunction in pregnant women: clinical dilemmas]

Hypothyroidism and hyperthyroidism are associated with maternal and neonatal pregnancy complications. Hypothyroidism should be treated with levothyroxine. Hyperthyroidism requires treatment with propylthiouracil or thiamazole. Subclinical hypothyroidism and thyroid auto-immunity are also associated with maternal and neonatal pregnancy complications. For both subclinical hypothyroidism and thyroid auto-immunity, treatment with levothyroxine has not yet been proven to be effective in preventing complications during pregnancy. For the Dutch population the following reference values for TSH levels during pregnancy may be used: 0.01-4.00 mU/l in the first and second trimesters. Reference values for the third trimester have not reported for this population, but are probably comparable with those of the second trimester.

Informatics of newborn screening for congenital hypothyroidism in Alberta 2005-08: flow of information from birth to treatment

OBJECTIVES

Alberta maintains a universal screening program for congenital hypothyroidism, a condition which, when treated promptly prevents neurological impairment. Because the program relies on multiple stakeholders working in different areas, it is not known how effective the overall process is in achieving timely treatment initiation. Our objective was to analyze and describe the informatics of this program.

METHODS

Data were collected from the Newborn Metabolic Screening Program and physician offices for hypothyroidism screen positive infants born between january 1, 2005 and May 31, 2008. Where data were available, times were determined for each interval: birth to sample collection, collection to receipt in central laboratory, receipt to report to the primary clinician, report to confirmatory test, and finally confirmation to thyroxin treatment.

RESULTS

Complete information was found on the stages up until report generation. Although subsequent intervals had less complete data, all but 5 of the 57 newborns were followed to the endpoint of treatment initiation or diagnosis exclusion. The program was consistent and efficient in collecting, analyzing and reporting results to the primary physician by a median of 8 days (range 4-14 days). Subsequent steps resulted in a median time from birth to treatment of 11 days. There were 4 cases for which delays in clinician follow-up led to treatment initiation at 27, 34, 56 and 70 days.

CONCLUSION

Newborn screening for congenital hypothyroidism in Alberta is efficient and consistent up until responsibility shifts to the community. Quality improvement work is needed to reduce potential delays.

Experience with intraamniotic thyroxine treatment in nonimmune fetal goitrous hypothyroidism in 12 cases

CONTEXT

Nonimmune fetal goitrous hypothyroidism is a rare condition that can induce obstetrical and/or neonatal complications and neurodevelopmental impairments such as those still seen in some patients with congenital hypothyroidism. Prenatal treatment to prevent these adverse outcomes is appealing, but experience is limited and the risk to benefit ratio controversial.

OBJECTIVE

The objective of the study was to evaluate the feasibility, safety, and effectiveness of intrauterine l-thyroxine treatment in a large cohort with nonimmune fetal goitrous hypothyroidism.

DESIGN

This was a retrospective study of 12 prenatally treated fetuses diagnosed between 1991 and 2005 in France.

METHODS

During pregnancy, goiter size and thyroid hormone levels were compared before and after prenatal treatment. At birth, clinical, laboratory, and ultrasound data were evaluated.

RESULTS

Prenatal treatment varied widely in terms of l-thyroxine dosage (200-800 microg/injection), number of injections (one to six), and frequency (every 1-4 wk). No adverse events were recorded. During pregnancy, thyroid size decreased in eight of nine cases and amniotic-fluid TSH levels decreased in the six investigated cases, returning to normal in four. However, at birth, all babies had hypothyroidism, indicating that intraamniotic TSH levels did not reliably reflect fetal thyroid function.

CONCLUSION

Our data confirm the feasibility and safety of intraamniotic l-thyroxine treatment for nonimmune fetal goitrous hypothyroidism. Although goiter size reduction is usually obtained, thyroid hormone status remains deficient at birth. Amniocentesis seems inadequate for monitoring fetal thyroid function. Further studies are needed to determine the optimal management of this disorder.

Iodine supplementation in pregnancy

People of all ages can be affected by iodine deficiency, however, pregnant women and children are especially at a high risk. Because of changes that occur in maternal thyroid hormone economy during pregnancy and the potential unfavorable effects of iodine deficiency on the offspring, an adequate dietary iodine intake throughout the pregnancy is highly important. Therefore, the World Health Organization, United Nations Children's Fund and International Council for the Control of Iodine Deficiency Disorders have proposed that dietary intake of iodine during pregnancy should be 200-300 microg/day to compensate for the augmented T4 requirements in pregnant women. It has been shown that in countries with a longstanding and well-established universal salt iodination program where iodine sufficiency has been reached, there is a fraction of pregnant women that still have low median urinary iodine concentration, which indicates insufficient dietary iodine. Studies performed in such countries emphasize that pregnant women should use multivitamin and/ or mineral tablets specifically prepared for the needs of pregnancy and containing iodine supplements. Only the United States of America and Canada have official recommendations concerning iodine supplementation. In other countries, no such firm decisions have yet been made by medical community and public health authorities. In Croatia, an iodine sufficient country, the situation is the same. There is a need to collect adequate data on iodine supplementation and urinary iodine during pregnancy, along with the universal salt iodination program, so that definitive conclusions can be made.

WITHDRAWN: Maternal iodine supplements in areas of deficiency

BACKGROUND

Iodine deficiency is the leading preventable cause of intellectual impairment in the world. Although iodine supplementation is generally considered to be safe, there is a possibility of high doses of iodine suppressing maternal thyroid function.

OBJECTIVES

The objective of this review was to assess the effects of iodine supplementation before or during pregnancy in areas of iodine deficiency.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group trials register.

SELECTION CRITERIA

All acceptably controlled trials of maternal iodine supplementation during pregnancy with clinical outcomes.

DATA COLLECTION AND ANALYSIS

Eligibility and trial quality were assessed by two reviewers.

MAIN RESULTS

Three trials involving 1551 women were included. In two trials, iodine supplementation was associated with a statistically significant reduction in deaths during infancy and early childhood (relative risk 0.71, 95% confidence interval 0.56 to 0.90). Iodine supplementation was associated with decreased prevalence of endemic cretinism at the age of four years (relative risk 0.27, 95% confidence interval 0.12 to 0.60) and better psychomotor development scores between four to 25 months of age.

AUTHORS' CONCLUSIONS

Iodine supplementation in a population with high levels of endemic cretinism results in an important reduction in the incidence of the condition with no apparent adverse effects.

[Screening for congenital hypothyroidism in neonates of Zhejiang Province during 1999-2004]

OBJECTIVE

To analyze the data of screening for congenital hypothyroidism (CH) newborns in Zhejiang Province during 1999-2004.

METHODS

The dried blood samples were collected on filter paper. The levels of thyroid-stimulating hormone (TSH) were measured by time-resolved fluoroimmunoassay, and the serum levels of TSH, triiodothyronine (T(3)) and thyroxine (T(4)) were detected by chemiluminescence. Infants with CH confirmed by neonatal screening were treated with levothyroxine (L-T(4)) initiated with 4-6 g/kg x d(-1 )for 2-3 years. Growth, development and intelligence status, scintigraphy or ultrasonography of thyroid, and bone age were investigated to evaluate the efficacy of therapy during follow-ups.

RESULT

A total of 1112784 neonates were screened for CH during 1999-2004 with a coverage rate of 63.5%. Of the 6750 suspected CH cases, 6335 (93.8%) were recalled. 764 cases of CH were confirmed with an average incidence rate of 1 case CH per 1457 newborns (1/1457). 244 of 764 patients were followed-up for more than 1.5-2 years. All of them received thyroid by scintigraphy or ultrasonography. Among them 189 cases were found with normal gland, 35 with hypogenetic gland, 11 with ectopic gland, and the remaining 9 didn't show any image of thyroid. The average score of development quotient (DQ) was 106. 9. Among them, the DQ score was less than 85 in 2 cases, less than 90 in 9 cases, less than 100 in 28 cases, and in 68 cases the DQ was greater than 100. The bone age of 122 CH infants was evaluated with the X-ray radiography. In 90 cases of them,the bone age was normal, and 32 cases had progressed from development delay to normal. The height and weigh measured in all 106 cases had reached the related age criteria. The evaluation indicated that 55 cases were found with primary CH, 169 with temporary CH and 20 with subclinical CH.

CONCLUSION

Neonatal screening for CH and regular treatment for CH patients are important for attaining normal body development and intelligence development of patients.

Thyroid disease in pregnancy and childhood

The subject of thyroid disease in pregnancy is receiving increasing attention from many scientific disciplines. Thyroid function in pregnancy is characterised by a T4 surge at 12 weeks declining thereafter. Serum thyroid hormone concentrations fall in the second half of pregnancy but there are few data on normal reference ranges. Fetal brain development depends on T4 transport into the fetus which in turn depends on sufficient maternal iodine supply. There is current concern that adequate iodisation is not present in large parts of Europe. There is increasing evidence that thyroid autoimmunity is associated with fetal loss but the mechanism is unclear and therapy requires carefully conducted studies. While hyperthyroidism in pregnancy is uncommon, effects on both mother and child are critical if untreated. The use of propylthiouracil is recommended together with measurement of TSH receptor antibodies at 36 weeks gestation. Women receiving thyroxine therapy for hypothyroidism or as suppressive therapy should have their dose increased by up to 50% during pregnancy. There are now substantial data to show deleterious effects on child IQ resulting from low maternal T4 (or high TSH) during gestation. Major advances in molecular biology have contributed to elucidation of many genetic causes of congenital hypothyroidism. However, the aetiology of the majority of cases is still unclear and further research is required. The presence of TPO antibodies in about 10% of pregnant women in early gestation is a predictor of an increased incidence of subclinical hypothyroidism during pregnancy and also of postpartum thyroid dysfunction. The latter condition occurs in 5-9% of women and 25-30% progress to permanent hypothyroidism. This review suggests that screening for thyroid function in early pregnancy and levothyroxine intervention therapy for maternal subclinical hypothyroidism should be considered but evidence is awaited. Screening for both thyroid dysfunction and thyroid antibodies ideally at a preconception clinic but certainly in early gestation is recommended.

[Real activity of Kraków endocrine group in Institute of Pediatrics CMUJ on the eradication of IDD in Polish children]

The authors present the investigations concerned the Iodine deficiency disorders (IDD) elimination in children living in South-East of Poland in last 15 years. To achieve the full success, what, as we know is possible, the monitoring and the exact control of the salt iodine supplementation according to the National Program of Iodine Deficiency Elimination (1999-2003) should be maintained. To avoid any negligence, the prompt education of the whole population is necessary, but yet especially the pregnant women. It is important to instruct them about the direct influence of iodine deficiency on the mental development of the fetus and the newborn.

Iodine supplementation for preventing iodine deficiency disorders in children

BACKGROUND

Iodine deficiency is the main cause of potentially preventable mental retardation in childhood, as well as causing goitre and hypothyroidism in people of all ages. It is still prevalent in large parts of the world.

OBJECTIVES

To assess the effects of iodine supplementation overall, and of different forms and dosages of iodine supplementation separately, in the prevention of iodine deficiency disorders in children.

SEARCH STRATEGY

The Cochrane Library, MEDLINE, EMBASE and reference lists, databases of ongoing trials and the Internet were searched. Date of latest search: October 2003.

SELECTION CRITERIA

We included randomised controlled trials and prospective controlled trials not using randomisation of iodine supplementation in children living in areas of iodine deficiency.

DATA COLLECTION AND ANALYSIS

Two reviewers did the initial data selection and quality assessment of trials independently. As the studies identified were not sufficiently similar and not of sufficient quality, we did not do a meta-analysis but summarised the data in a narrative format.

MAIN RESULTS

Twenty-six prospective controlled trials were related to our question, assessing a total of 29613 children. Twenty of them were classified as being of low quality, six of moderate quality. Most studies used iodised oil as a supplement, but other supplements were also used. The intervention groups were compared to a non-supplemented control group, different doses or different forms of iodine supplementation. There was a clear tendency towards goitre reduction with iodine supplementation; this was significant in several studies. Significant differences in physical development were not seen, except in one study. Results for differences in cognitive and psychomotor measures were mixed, with only few studies showing a positive intervention effect. One study suggested that infant mortality was lowered after iodine supplementation. Most studies showed a significant increase in urinary iodine excretion and levels recommended by the WHO were reached in most cases after supplementation. Thyroid-stimulating hormone (TSH) levels were significantly reduced in one study. In 1.8% of the children investigated, adverse effects were found, most of them were minor and transient.

REVIEWERS' CONCLUSIONS

Despite most of the included studies being of low quality, the results suggest that iodine supplementation, especially iodised oil, is an effective means of decreasing goitre rates and improving iodine status in children. Indications of positive effects on physical and mental development and mortality were seen, although results were not always significant. Adverse effects were generally minor and transient. Insufficient evidence was available on non-oil supplements. High quality controlled studies investigating relevant long term outcome measures are needed to address the question of the best form of iodine supplementation in different population groups and settings.

Iodine deficiency in Europe and its consequences: an update

This paper updates the information on the prevalence of the disorders induced by iodine deficiency (IDD) in Europe. Thirty-two European countries were still affected by mild to severe iodine deficiency in the late 1990s. The most severely affected countries were in Eastern Europe, including Central Asia, but Western Europe was also still affected. National surveys recently conducted in 11 of these countries show that, with the exception of the Netherlands, none has yet reached a state of iodine sufficiency, though very significant improvement in the situation has been evidenced in many of them, e.g. Poland, Bulgaria and Macedonia. The consequences of persisting iodine deficiency are goitre, hyperavidity of the thyroid for iodide (which increases the risk of thyroid irradiation in the event of a nuclear accident) and subclinical hypothyroidism during pregnancy and early infant (with a concomitant risk of minor brain damage and irreversible impairment of the neuropsychointellectual development of offspring). Access to iodised salt at the household level in European countries affected by IDD increased from 5%-10% in 1990 to 28% in 1999. This constitutes encouraging progress. However, in terms of access of iodine-deficient countries to iodised salt, Europe remains the worst region in the world, as shown by the fact that the mean figure worldwide in 1999 was 68%. In Latin America it even reached 90%. Salt iodisation has to be further implemented in Europe. Until that goal is achieved, iodine supplementation in those groups most sensitive to the effects of iodine deficiency (pregnant and lactating women and young infants) will have to be considered in the most severely affected areas.

[Iodine deficiency in the Russian Federation]

Epidemiological surveys for iodine deficiency (ID) were made in 30 regions of Russia in 1992 to 1999. A total of 40,999 individuals aged 7 to 17 years were examined. The advent of new assessments of the thyroid and new indicators of iodine deficiency has changed approaches to epidemiological surveys. The WHO standards for estimating the prevalence and severity of ID have been introduced into Russian practice. In Central Russia, the lowest (median 30-58 micrograms/l) iodine concentrations were found in rural dwellers; in more urbanized areas (cities, towns) the median was 50-78 micrograms/l. ID was more pronounced in the regions of East Russia where it was predominantly moderate (median 30-52 micrograms/l). In some areas, ID was severe (median 16-20 micrograms/l). As the severity of ID increases, the incidence of such conditions, as goiter, hypothyroidism, endemic cretinism is on the rise. Mild to moderate goiter endemia prevailed in Central Russia. The manifestations of goiter endemia were more pronounced in rural children (18-30%) than in urban ones (8-14%). East Russia was marked by moderate to severe goiter endemia (8-14%): the incidence of goiter ranged from 17 to 40%. There were only sporadic cases of goiter in some areas of the Sakhalin Region. In the Moscow and Voronezh Regions and the Republic of Kalmykia there were areas showing a high goiter incidence which did not correspond to the level of ID. An epidemiological analysis has indicated that dietary and water iodine intake is decreased in most regions of Russia. The actual dietary iodine intake was 40-80 micrograms/day, i.e. 2-3 times of the recommended allowance (150 micrograms). The Endocrinology Research Center has tested different models of preventive and therapeutical measures for eliminating iodine deficiency-caused diseases by using iodinated foodstuffs (salt, bread, butter) ad iodine medicaments.

[From gene to disease; POU1F1- and PROP1-mutations in pituitary hormone deficiency]

Multiple pituitary hormone deficiency can be caused by mutations in at least three pituitary transcription factors: POU1F1 (formerly called PIT1), PROP1 or HESX1. The role of the various pituitary transcription factors in pituitary ontogeny has been elucidated in part for the mouse. In humans, mutations in POU1F1 result in a total deficiency of growth hormone and prolactin, and a variable deficiency of TSH. Cases of mutations in PROP1 exhibit the same deficiencies, with additional deficiencies of gonadotrophins and a variable deficiency of ACTH. In the Netherlands, cases of multiple pituitary hormone deficiency are not only detected on the basis of the classical signs and symptoms of pituitary deficiency, but also by means of screening on congenital hypothyroidism with an incidence of approximately 1:20,000.

[The influence of iodine deficiency during pregnancy of fetal and neonatal development]

The iodine is fundamental substrate for thyroid hormones synthesis. Thyroxine and triiodothyronine play a crucial role in human brain development and maturation. It is well known, that not only fetal, but also maternal thyroid hormones are essential for normal prenatal central nervous system development. During pregnancy complex changes of maternal thyroid function occur and they are influenced by the maternal iodine supply. With decreasing iodine intake, maternal goiter and hypothyroxinemia as well as fetal and neonatal hypothyroidism become more prevalent. The severity of iodine deficiency and hypothyroidism in the mother during early and midgestation is related to the severity of the neural damage in the fetus. In severe iodine deficiency, central nervous system damage is already irreversible at birth and can only be prevented by correction of the maternal iodine deficiency early in pregnancy. Therefore iodine supplementation during pregnancy is now strongly recommended.

Iodine deficiency disorders in Europe

Iodine deficiency disorders (IDD) are related to the degree of iodine deficiency. In European countries, characterized by mild to moderate iodine deficiency, neurological deficits or minor neuropsychological impairments have been described. Urinary iodine excretion (UIE) ranged from 30 to 170 mcg/L, 141 millions of people were at risk of IDD, 97 millions were affected by goiter and 0.9 millions had an impaired mental development. Iodine prophylaxis is devoid of adverse reactions with the exception of sporadic cases of transitory hyperthyroidism, associated to the severity of iodine deficiency before the prophylaxis. The International Council for Control of IDD recommends an universal iodine prophylaxis, instituted gradually in severe iodine deficient countries. The total cost of universal iodine prophylaxis is very cheap compared to the social cost of goiter and cretinism. In conclusion, most European countries are still characterized by mild to moderate iodine deficiency. Iodine prophylaxis programs are already operating, its cost is irrelevant with respect to the undebatable beneficial impact on the health. Adverse effects are not observed except in severe iodine deficient areas where iodine intake was abruptly increased.

Endemic goiter and cretinism: an update on iodine status

Iodine deficiency is the most prevalent correctable cause of brain damage in the world. Over the past 15 years, great progress has been made towards the elimination of iodine deficiency, principally through universal salt iodization. Much more needs to be done for countries that are lagging in the effort or that have weak systems for sustaining it. The key to maintaining optimal iodine intake is regular monitoring, usually by the measurement of urinary iodine concentration, linked to a prompt response in the event of abnormal results. If the present momentum continues then global iodine sufficiency is possible and, in a landmark achievement, iodine deficiency will be the first major non-infectious disorder to be eliminated.

Iodine and neuropsychological development

The establishment of the essential link among iodine deficiency, thyroid function and brain development has emerged from a fascinating combination of clinical, epidemiologic and experimental studies. The central human phenomenon that focuses this relationship is the condition of endemic cretinism, described from the Middle Ages and characterized in its fully developed form by severe brain damage, deaf mutism and a spastic state of the hands and feet. The demonstration of the prevention of cretinism in a double-blind controlled trial with injections of iodized oil in Papua New Guinea (1966-1970) established the causal role of iodine deficiency in cretinism by an effect on the developing fetal brain. Cretinism could not be prevented unless the iodized oil was given before pregnancy. Iodine deficiency is now regarded by the WHO as the most common preventable cause of brain damage in the world today, with at least 30 million suffering from this preventable condition. Since 1986 the international NGO, the International Council for Control of Iodine Deficiency Disorders, has worked closely as an expert group with WHO and UNICEF in assisting countries with a program of universal salt iodization for the elimination of iodine deficiency as a cause of brain damage by the year 2000. In 1996, WHO reported that 56% of the population of 83 developing countries now had adequate access to iodized salt. This represents an increase of 750 million since 1990 with protection of 12 million children.

Maternal iodine supplements in areas of deficiency

BACKGROUND

Iodine deficiency is the leading preventable cause of intellectual impairment in the world. Although iodine supplementation is generally considered to be safe, there is a possibility of high doses of iodine suppressing maternal thyroid function.

OBJECTIVES

The objective of this review was to assess the effects of iodine supplementation before or during pregnancy in areas of iodine deficiency.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group trials register.

SELECTION CRITERIA

All acceptably controlled trials of maternal iodine supplementation during pregnancy with clinical outcomes.

DATA COLLECTION AND ANALYSIS

Eligibility and trial quality were assessed by two reviewers.

MAIN RESULTS

Three trials involving 1551 women were included. In two trials, iodine supplementation was associated with a statistically significant reduction in deaths during infancy and early childhood (relative risk 0.71, 95% confidence interval 0. 56 to 0.90). Iodine supplementation was associated with decreased prevalence of endemic cretinism at the age of four years (relative risk 0.27, 95% confidence interval 0.12 to 0.60) and better psychomotor development scores between four to 25 months of age.

REVIEWER'S CONCLUSIONS

Iodine supplementation in a population with high levels of endemic cretinism results in an important reduction in the incidence of the condition with no apparent adverse effects.

Metabolic maladaptation: individual and social consequences of medical intervention in correcting endemic hypothyroidism

Endemic hypothyroidism has been studied in a Central African population in remote Congo (ex-Zaire) to investigate the prevalence, severity, causes, and potential control of this disorder, with questions as to why this disease is conserved, and whether it confers any adaptive advantage in this resource-constrained environment. Iodine deficiency, cassava goiterogens, and selenium deficiency were found to be the factors implicated in the severe hypothyroidism expressed in congenital cretinism and high goiter incidence in this isolated population, which continues to be under observation following medical intervention. Profound hypothyroidism was encountered in whole village populations as measured by serum thyrotropin determinations ranging from very high to over 1000 IU, and thyroxin levels ranging from low to undetectable; cretinism rates were as high as 11% and goiter incidence approached 100%. Assessment of endocrinologic status, caloric requirement, energy output, fertility, and ecologic factors was carried out before and during iodine repletion by depot injection. Hypothyroidism was corrected and cretinism eliminated in the treatment group, with goiters reduced in most instances (with regrowth exhibited in some who escaped control) and some symptomatic goiter patients were offered surgical treatment for respiratory obstruction. Individual patient benefits, including improved strength and increased energy output, were remarkable. The social and developmental consequences observed within the collective groups of treated patients were remarkable for an increase in caloric requirement and a dramatic increase in fertility that led to quantitative as well as qualitative increases in resource consumption. Micronutrient iodine repletion was not accompanied by any concomitant increase in macronutrient supply, and hunger and environmental degradation resulted. The highly prevalent disease of hypothyroidism is found in highest incidence in areas of greatest resource constraint. It may be that hypothyroidism is conserved in such areas because it may confer adaptive advantage in such marginal environments as an effect, as well as a cause, of underdevelopment. Hypothyroidism may limit energy requirements, fertility, and consumer population pressure in closed ecosystems that could otherwise be outstripped. Single factor intervention in a vertical health care program not sensitive to the fragile biologic balance and not part of a culture-sensitive development program might result in medical maladaptation.

Persistence of iodine deficiency 25 years after initial correction efforts in the Khumbu region of Nepal

AIMS

To assess the current status of, and understanding about iodine deficiency disorders among Sherpa residents of the Khumbu region of Nepal, 25 years after the introduction of iodised oil injections.

METHODS

Several groups of Khumbu Sherpas were studied and goitre rate, urinary iodine level and cretinism prevalence were measured as indicators of iodine deficiency. Subjects were also questioned in detail about their food consumption, with particular reference to salt use, and about their understanding of the causes and treatment of iodine deficiency disorders.

RESULTS

The prevalences of goitre, deaf-mutism and cretinism were 21%, 1.3% and 0.5% respectively (compared to 92%, 4.7% and 5.9% in 1966). No cretins had been born since 1966. The median urine iodine concentration was 35 microg/L. Most people preferred uniodised Tibetan rock salt, although 44% regularly consumed iodised salt. All granulated salt tested from the local market contained adequate amounts of iodine. Only 11% of those surveyed knew that goitre was caused by iodine deficiency

CONCLUSIONS

Although prevalences of iodine deficiency disorders are much less than 30 years ago, iodine deficiency continues to be a major problem in Khumbu and demands a clear control strategy, combining ongoing iodine supplementation and education. Iodised salt is usually the best approach to control of iodine deficiency disorders for most regions of the world but the Khumbu experience shows that local cultural and commercial factors can severely limit its impact. To be successful, control programme for iodine deficiency disorders also needs assessment of the salt trade, monitoring, education and occasional targeted interventions with iodised oil or other supplements.

[Efficacy and safety of iodine prophylaxis]

Iodine deficiency and iodine deficiency disorders (IDD) are still present in developing countries as well as in some European areas. It is well known that iodine deficiency correction prevents endemic goiter and other IDD. Iodized oil has been shown to reduce goiter prevalence and cretinism in African countries. In countries where iodine prophylaxis is performed since many years (USA, Switzerland, Scandinavian countries) IDD are dramatically reduced. One example of the efficacy of iodine prophylaxis through iodized salt was reported in a Tuscan village were urinary iodine excretion increased from 47 micrograms/l in 1981 to 130 micrograms/l in 1991. Goiter prevalence in schoolchildren dropped from 60% in 1981 to 8.1% in 1991. In the same children neuropsychological performances were evaluated showing a reduction of motor response to perceptive stimuli assessed by measurement of reaction times in children born before the beginning of iodine prophylaxis. Iodine prophylaxis has no side effects, although a transitory increase of hyperthyroidism has been reported in the past and recently in African countries. A reevaluation by the experts of the International Council for the Control of Iodine Deficiency Disorders (ICCIDD) has pointed out that this phenomenon is not relevant with respect to the efficacy of iodine prophylaxis. In conclusion, universal iodine prophylaxis prevents endemic goiter and other IDD, without side effects.

Alterations of neonatal thyroid function

Recent progress has been made in understanding the pathogenesis of neonatal thyroid disorders. Autosomal recessive inheritance of mutations of the thyroid peroxidase and thyroglobulin genes has been described in some patients with congenital hypothyroidism (CH) and a family history of CH. Autosomal recessive inheritance of mutations of the thyrotrophin (TSH) receptor gene has also been reported in patients with CH and thyroid hypoplasia, and autosomal dominant mutations of the PAX8 gene have been described in patients with different forms of thyroid dysgenesis. These discoveries are important for patients with CH diagnosed by neonatal screening, as these patients will have normal fertility. The molecular genetic analysis of mutations of the TSH gene in patients with familial and sporadic cases of isolated central CH, who are missed by TSH screening programmes, now enables rapid diagnosis and appropriate therapy in the neonate. In newborn infants with severe non-autoimmune hyperthyroidism, autosomal dominant gain-of-function mutations in the TSH receptor gene have been demonstrated. In these patients, molecular genetic studies are extremely helpful in therapeutic decision making, as early thyroid ablation is the only effective treatment that avoids the sequelae of long-term hyperthyroidism. Molecular genetic studies are therefore useful in the diagnostic work-up of neonatal thyroid alterations.

Newborn screening for certain treatable inborn errors of metabolism in Alexandria

The study was conducted on two groups of newborn infants: Group A; a random sample of 3000 infants attending different Health offices in Alexandria for BCG vaccination. Their ages ranged from 5-120 days with a mean age of 39.9 days. Group B; included all the infants born to high risk families attending the clinic of Human Genetics Department, Medical Research Institute (9 infants; 7 with family history of PKU and 2 with family history of congenital hypothyroidism). Their ages ranged from 7 to 60 days with a mean age of 18 days. The newborn infants of the two groups were screened for three treatable inborn errors of metabolism, phenylketonuria "PKU", galactosemia and congenital hypothyroidism with the aim of early detection and therapy to prevent mental retardation. In group A; one baby with transient hyperphenylalaninemia (HPA) (0.33%) and one presumptive case of galactosemia (0.33%) were found. Initial positive results were found in eleven infants they had high levels of thyroid stimulating hormone (TSH). On reevaluation of nine infants of them they were all euthyroids. In Group B, four infants were detected among the infants of PKU families. After confirmation of these results breast feeding was stopped at once and the infants started their dietary management and were kept on it with follow up and periodic evaluation of the adequacy of treatment.

Administration of iodized oil during pregnancy: a summary of the published evidence

This brief review of the available studies confirms that the administration of iodized oil before or during pregnancy prevents endemic cretinism and brain damage by correcting iodine deficiency and thyroid function in pregnant women, fetuses, neonates, infants and children. The potential benefits derived from using iodized oil immediately before or during pregnancy greatly outweigh the potential risks in areas of moderate and severe prevalence of iodine-deficiency disorders, where iodized salt is not yet available.