PCBs can damage the thyroid gland.  This may cause hypothyroidism or hyperthyroidism.
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thyroid, hypothyroid, thyroid hormones, thyroid diseases, hyperthyroid, thyroid problems, thyroid disorders, hypothyroidism, hyperthyroidism, thyroid condition, thyroid gland, thyroids, thyroiditis, thyroid health
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Thyroid Function, PCBs, and Brain Damage

thyroid, hyprothyroid, thyroid hormones, thyroid diseases, hyperthyroid, thyroid problems, thyroid disorders, hypothyroidism, hyperthyroidism, thyroid condition, thyroid gland, thyroids, thyroiditis, thyroid health
Introduction

Scientists generally agree that PCBs alter thyroid hormones in the human body. The following 18 human studies and 42 study reviews bear this out. (More than 100 additional thyroid studies of animals, birds and fish will be added to this website in the near future.) 

PCBs have a shape very similar to thyroid hormones, which allows them to interfere or compete with normal hormones. Certain types of PCBs are more potent than others.

The thyroid is a butterfly shaped gland which wraps around the front part of the windpipe just below the Adam's apple. It produces hormones which influence essentially every organ, every tissue and every cell in the body. Thyroid hormones regulate the body's metabolism and organ function, affecting heart rate, cholesterol level, body weight, energy level, muscle strength, skin condition, menstrual regularity, memory and many other conditions.
 

When a mother has thyroid abnormalities during pregnancy, it can have serious consequences for the child. Thyroid hormones provide chemical signals which direct the development of the egg from one cell as it divides to become every different organ in the child’s body.  In particular, a normal mix of thyroid hormones is essential for healthy behavioral, intellectual, and neurological development in the child’s brain. Evidence is increasing that PCB exposures to children in the womb are neurotoxic --- toxic to the developing brain. (see PCB Baby Studies)

Adults can also suffer serious health problems. Currently, 13 million Americans suffer from a thyroid disorder, but 8 million of them don't know it. Approximately 1 in 8 women will develop a thyroid disorder during her lifetime. More than half of American women over 40 experience three or more common symptoms of thyroid disorder (but 75% haven't discussed this with a doctor.)
 
The most common thyroid disorder is an underactive thyroid gland, or hypothyroidism. This results when the thyroid fails to produce enough hormones. Less frequently, an overactive thyroid condition, or hyperthyroidism, occurs when the thyroid produces more thyroid hormone than is needed. If properly treated, patients with thyroid disorders can lead normal, active lives. Thyroid disorders can be detected with a simple blood test. If you are experiencing any of the symptoms related to thyroid disorders, ask a physician about getting a TSH test to ensure that your thyroid gland is operating efficiently. (For more information, visit the Links in this section.)

The epidemic of thyroid disorders in this country raises serious questions. Could the high rates be linked partly to the widespread contamination of the American food supply over the past 50 years with PCBs and other toxic chemicals? Is it possible that many of our children who suffer from increased rates of behavioral problems and learning disabilities (such as Attention Deficit Hyperactivity Disorder or Autism) are damaged as a result of PCB exposure?

Thyroid Disorders, Hypothyroidism and Hyperthyroidism

One of the most disturbing findings of the studies listed below is that even background levels of PCBs in the general population have been found to influence thyroid hormone levels. This means that those of us who reside in Northeast Wisconsin, and Upper Michigan along Lake Michigan, and who receive additional exposures to PCBs through fish-eating, duck-eating, breathing, or skin contact, are being dosed above background PCB levels which could increase the likelihood of thyroid effects on ourselves and our children. However, no local studies have been conducted to determine the rates of thyroid disorder in our region relative to PCB exposures. Such studies are clearly needed.

Warnings are Needed --- Local People Need Thyroid Tests!

Our government health agencies should be encouraging PCB exposed residents to get tested for thyroid disorder, so they can be treated and not suffer needlessly. Such warnings should have been issued 20 years ago, as medical evidence became clearer.

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Symptoms of Untreated Hypothyroidism in Adults

  • Cardiovascular System (slowed heart rate, increased diastolic blood pressure)
  • Central Nervous System (decreased concentration, loss of interest and/or pleasure, depression)
  • Gastrointestinal Tract (decreased secretion of digestive juices, constipation)
  • Musculoskeletal System (muscle stiffness, cramps, weakness, pain, muscle stretch reflexes, muscle enlargement, atrophy, joint pain and stiffness)
  • Kidneys (fluid retention and edema)
  • Liver (increased LDL cholesterol in the blood, elevated triglycerides in the blood)
  • Reproductive System (abnormally heavy menstrual bleeding, missed ovulation, decreased fertility, missed menstrual periods)
  • Skin and Hair (thickening and dryness of the skin, dry, coarse hair and/or loss of hair, loss of lateral eyebrow hair)
thyroid, hyprothyroid, thyroid hormones, thyroid diseases, hyperthyroid, thyroid problems, thyroid disorders, hypothyroidism, hyperthyroidism, thyroid condition, thyroid gland, thyroids, thyroiditis, thyroid health
Symptoms of Untreated Hyperthyroidism in Adults
  • Cardiovascular System (increased heart rate, increased diastolic blood pressure, heart flutter - atrial fibrillation)
  • Central Nervous System (difficulty sleeping, difficulty concentrating, nervousness, irritability, changes in vision)
  • Gastrointestinal Tract (increased frequency of bowel movements, increased appetite, weight loss)
  • Musculoskeletal System (fatigue and muscle weakness)
  • Kidneys (leg edema)
  • Reproductive System (decreased menstrual flow, reduced fertility)
  • Endocrine System (enlarged thyroid)
  • Other (intolerance to heat, increased sweating, enlargement and protruding of the eyes)
thyroid, hyprothyroid, thyroid hormones, thyroid diseases, hyperthyroid, thyroid problems, thyroid disorders, hypothyroidism, hyperthyroidism, thyroid condition, thyroid gland, thyroids, thyroiditis, thyroid health

Summary of Results --- 18 Human Thyroid PCB Studies

(each entry represents a finding in a study --- some studies had multiple findings)

Keep in mind that not all studies are equal in size or quality. Some examine the effects of old PCB commercial mixtures (which had variable composition), or just one or two individual types of PCBs (out of 209 possible.) Some of the studies are from the 1970s when scientists were just learning about thyroid effects. Some studies use high and some use low doses of PCBs. In some cases, the exact PCB dose was unknown. The types of PCBs which have lingered in our area and accumulated in Fox River and Green Bay fish are likely to be the more toxic and persistent PCB types (which are most similar to thyroid hormones.)

  • PCB exposure during adulthood was associated with impairments in memory and learning
  • executive and visual-spatial function were unaffected
  • PCBs and dioxins as found in the normal population have an effect on thyroid metabolism in humans.
  • TT3 and TT4 levels decreased with increasing levels of PCBs and dioxin
  • TSH levels were significantly elevated in newborns with higher PCB and dioxin levels
  • decrease in TT4 and FT4 levels in human infants
  • increase in TSH levels
  • psychomotor development was negatively influenced
  • increasing PCB and dioxin doses correlate with decreasing thyroid hormones in mothers’ milk and blood plasma
  • increasing dioxin exposure correlates with higher thyroid stimulating hormone (TSH) in newborn infants
  • background levels of PCBs are only slightly related to serum concentration of total thyroxine, free thyroxine, and thyroid stimulating hormone at birth
  • dioxin linked to increased total thyroxine (tT4) --- (certain PCBs are dioxin-like)
  • dioxin linked to increased thyroxine-binding globulin
  • dioxin linked to increased thyrotropin (TSH)
  • increased dioxins (& related compounds) correlate with reduced thyroxine (T4) levels (certain PCBs are dioxin-like)
  • slight alteration of the thyroid metabolism (still within normal limits) after increased exposure to dioxides and PCB
  • no grounds to advise against breast feeding
  • no impaired thyroid function, as revealed by plasma levels of TSH and thyroxine
  • serum triiodothyronine (T3) and thyroxine (T4) levels were significantly higher
  • hyperthyroxinemia
  • T4 ratio was significantly higher
  • thyroglobulin antibody in Yusho patients is not frequent and it may be associated with blood PCB concentration
  • 8.6% had elevated TSH levels
  • increased levels of PCBs, dioxins and furans in breastmilk correlated with decreased thyroxine (T4) and triiodothyronine (T3)
  • background levels of PCBs, dioxins and furans may affect thyroid hormone status in infants
  • enlarged thyroids
  • no relation between PCB and thyroid hormone or creatine kinase and thyroid hormone was observed
  • significant differences in thyroxine (T4) and T4-RT3 index, correlated with PCB exposure
  • thyroid function was normal.
  • thyroid changes occurred, consistent with PCB exposure
  • more research is needed, to include thyroid status
thyroid, hyprothyroid, thyroid hormones, thyroid diseases, hyperthyroid, thyroid problems, thyroid disorders, hypothyroidism, hyperthyroidism, thyroid condition, thyroid gland, thyroids, thyroiditis, thyroid health

Summaries of 40 Study Reviews

(each entry represents a finding in a study --- some studies had multiple findings)

  • altered thyroid hormones have been consistently seen in human populations at background levels of PCB exposure
  • PCBs bear a striking structural resemblance to thyroid hormones
  • PCBs act as agonists, antagonists, and partial agonists to thyroid hormones (ie: PCBs interfere)
  • inappropriate levels of thyroid hormones at key moments can produce permanent brain damage
  • PCBs and dioxins are structurally similar to thyroid hormones
  • PCBs and dioxins have binding characteristics similar to thyroid hormones
  • PCBs and dioxins can either decrease or mimic the biological action of thyroid hormones
  • deficient or excessive thyroid hormones can cause irreversible neurological damage in the womb or infancy
  • mothers or children with existing thyroid disorders could experience greater harm even at low PCB levels which leave other people unharmed
  • PCB exposed adults with existing thyroid disorders may face greater risk of developing brain, motor, or metabolic dysfunction
  • evidence is increasing that PCBs impair learning, memory and attentional processes in children
  • such neurodevelopmental effects may be linked to alterations in hormone binding to the thyroid hormone receptor
  • thyroid hormones are essential for normal behavioral, intellectual, and neurological development
  • PCBs alter serum thyroid hormone levels in humans
  • hydroxylated PCBs (metabolized in the body) compete with thyroid hormones for binding sites
  • PCBs and dioxins can alter human thyroid hormone status
  • thyroid hormone alterations have been observed in mothers and infants exposed to background levels of PCBs
  • thyroid hormones stimulate development of the central nervous system in embryos
  • the thyroid system is linked to other important body systems that use similar biochemical signals
  • PHAHs [which include PCBs] can disrupt the thyroid hormone system at a multitude of interaction sites, which may have a profound impact on normal brain development
  • adverse effects may occur within the range of current background human body levels of PCBs in the general population
  • use of the dioxin Toxic Equivalency Factor (TEF) may underestimate risk of neurodevelopmental effects
  • hyper- and hypothyroidism can be caused by PCBs and dioxins
  • the hypothalamic-pituitary-ovarian-axis can be damaged directly by contaminants, but also indirectly through changes in thyroid hormone secretion.
  • thyroid effects can be highly relevant to prenatal and postnatal development
  • Toxic Equivalency Factors (TEFs) are inappropriate for estimating PCB thyroid effects
  • only certain types of PCBs affect thyroid hormone levels
  • PCBs in concentrations commonly found in humans can induce significant increases in the levels of free thyroxine in the serum by competing with the thyroid hormone binding proteins present in the serum --- leading to hypothyroidism
  • PCB commercial mixtures (Aroclors) have been shown to produce thyroid alterations
  • even low doses of PCBs interact with the thyroid system
  • dioxins are linked to subcutaneous sarcomas and tumors of the thyroid (cancer) --- (certain PCBs are dioxin-like)
  • PCBs exhibit hormonal activity and bind transthyretin, a thyroid hormone binding protein
  • PCBs are thyroid disrupting
  • PBBs (polybrominated biphenyls) may also affect thyroid hormone status
  • hydroxylation (metabolic conversion) of PCBs or PBBs may play an important role
  • hydroxylated PCBs (metabolized) are potent inhibitors of T2 (diiodothyronine) and probably T3 (triiodothyronine)
  • inhibition of T3 (a thyroid hormone) may cause developmental neurotoxicity (brain damage)
  • two models indicate a structural relationship between some PCBs and thyroid hormones
  • PCBs are reactive with thyroxine (T4)
  • PCBs are accumulated in the thyroid gland
  • hydroxylated PCBs may decrease thyroid hormone levels
  • 60% of 65 other industrial chemicals (mostly pesticides) also interfered with thyroid hormones (therefore, humans face combined impacts)
  • subclinical effects may be present in the background population of humans
  • organochlorine compounds (such as PCBs) are associated with abnormal thyroid function
  • PCBs, dioxins and furans are associated with disease of the thyroid
  • thyroid hormones may play a role in oxidative DNA damage which leads to cancer
  • PCBs are implicated in tumor (cancer) induction as an indirect result of oxidative DNA damage
  • common food poisoning symptoms include thyroid function changes
  • dioxin in breast milk may affect infants’ thyroid function
  • more studies of thyroid functionality are needed, because human exposure to PCBs is inevitable
  • alterations in neurotransmitter systems and thyroid function may underlie behavioral dysfunction
  • hexachlorobenzene correlates with thyroid cancer --- [hexachlorobenzene is closely related to certain PCBs]
  • PCBs and dioxins reduce circulating thyroid hormone levels
  • PCBs cause blood-level alterations and affect the circadian rhythm
  • thyroid function is detrimentally impacted by chemical exposures
  • thyroid function is adversely affected by certain man-made chemicals
  • PCBs have known or suspected adverse effects on the human thyroid
  • need to investigate the potential harm posed by these factors in the quantities commonly encountered
  • more research is needed
  • new legislation requires EPA to test chemicals for anti-thyroid activities and effects on steroid/thyroid hormone synthesis
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Human Thyroid PCB Studies

This is not a complete list of all studies on this topic. For more studies, visit the TOXNET database operated by the National Library of Medicine (the source of these abstracts). 

Study #1

  • PCB exposure during adulthood was associated with impairments in memory and learning
  • executive and visual-spatial function were unaffected
An association between in utero polychlorinated biphenyl (PCB) exposure and impaired childhood intellectual functioning has been reported, but the potential impact of PCB exposure during adulthood on intellectual functioning has received little attention. We assessed the impact of PCBs and other fish-borne contaminants on intellectual functioning in older adults. The subjects were 49- to 86-year-old Michigan residents recruited from an existing cohort. Fish eaters ate > 24 lb of sport-caught Lake Michigan fish per year and non-fish eaters ate < 6 lb of Lake Michigan fish per year. A battery of cognitive tests including tests of memory and learning, executive function, and visual-spatial function was administered to 180 subjects (101 fish eaters and 79 non-fish eaters). Blood samples were analyzed for PCBs and 10 other contaminants. We evaluated cognitive outcomes using multiple regression. PCBs and dichlorodiphenyl dichloroethene (DDE) were markedly elevated in fish eaters. After controlling for potential confounders PCB, but not
DDE, exposure was associated with lower scores on several measures of memory and learning. These included the Weschler Memory Scale verbal delayed recall (p = 0.001), the semantic cluster ratio (p = 0.006), and list A, trial 1 (p = 0.037), from the California Verbal Learning Test. In contrast, executive and visual-spatial function were not impaired by exposure to either PCBs or DDE. In conclusion, PCB exposure during adulthood was associated with impairments in memory and learning, whereas executive and visual-spatial function were unaffected. These results are consistent with previous research showing an association between in utero PCB exposure and impairments of memory during infancy and childhood.  (Schantz et al, 2001)

Study #2

  • PCBs and dioxins as found in the normal population have an effect on thyroid metabolism in humans.
  • TT3 and TT4 levels decreased with increasing levels of PCBs and dioxin
  • TSH levels were significantly elevated in newborns with higher PCB and dioxin levels
  • mothers and 418 children studied
Dioxins and polychlorinated biphenyls (PCBs) are potentially hazardous compounds that can alter the thyroid hormone homeostasis as shown in animal studies. We investigated thyroid hormone levels in women around delivery and in their infants just after delivery, at 2 wks and 3 months of age. Dioxin and PCB levels were measured in human milk and in maternal and umbilical cord plasma. (Table: see text). Conclusions: 1) TT3 and TT4 levels are negatively correlated to PCB and dioxin levels as can be found in the Dutch population. 2) TSH levels in newborns are significantly elevated at higher PCB and dioxin exposure. 3) These results indicate that PCBs and dioxins as found in the normal population have an effect on thyroid metabolism in humans. (Koopman-Esseboom et al, 1994)

Study #3

  • decrease in TT4 and FT4 levels in human infants
  • increase in TSH levels
  • psychomotor development was negatively influenced
  • mothers and 418 children studied
A prospective longitudinal follow-up study assessing neurodevelopment (according to Prechtl) was done in a cohort of 418 Dutch Caucasian full-term infants in the second week after birth and at 18 months of age. PCB levels were measured in maternal plasma in the last month of pregnancy and in umbilical cordblood. Dioxins were measured in breastmilk and formula samples. Half of the infants were breast-fed, the other half formula-fed. In the second week after birth, exposure to higher levels of PCBs and dioxins was related to reduced neonatal neurological optimality scores and to a higher incidence of hypotonia. At 18 months of age higher transplacental exposure to PCBs was related to reduced neonatal neurological optimality scores. There was no relation with clinical relevant neurological abnormalities. In the Rotterdam cohort, thyroid hormone levels were measured. Higher exposure to PCBs and dioxins was related to a decrease in TT4 and FT4 levels and an increase in TSH levels in the infants. Mental development was not negatively influenced. However, psychomotor development was negatively influenced by a higher exposure to PCBs and dioxins. (Koopman-Esseboom et al, 1995)

Study #4

  • increasing PCB and dioxin doses correlate with decreasing thyroid hormones in mothers’ milk and blood plasma
  • increasing dioxin exposure correlates with higher thyroid stimulating hormone (TSH) in newborn infants
  • studied 400 mother-infant pairs
Polychlorinated biphenyls (PCBs) and dioxins are potentially toxic compounds which occur widely in the environment. Their effects on the growth and development of infants at the levels currently found in highly industrialised western countries is not well known. This Dutch multicenter study, combining animal and human studies, tries to answer this question. Animal studies showed that PCB 169, given once during pregnancy at a dose of 1.8 g kg-1 bodyweight, has an effect on developmental parameters, dopamine regulation and fertility. Effects on thyroid hormones were also found in animals, probably due to both a competitive binding of PCB metabolites to the thyroxine binding protein and increased glucuronidation. Perhaps to compensate for this, an increased diodase activity in the brain was found. Human studies involved 400 mother-infant pairs, half of them being breast-fed, the other half were fed a formula devoid of PCBs and dioxins. PCB levels were measured in serum and dioxin and PCB levels in breastmilk. Levels were found to be as high as previously found in highly industrialised countries. Growth and development were carefully documented, but no data are as yet available. In pregnant women, a significant negative correlation was found between some dioxin and PCB congeners in milk and plasma thyroid hormones, while newborn infants showed higher thyroid stimulating hormone (TSH) at higher levels of dioxin exposure. In summary, data from this combined multicenter study involving animals and humans increases our insight into the potentially negative effects of PCBs and dioxins on growth and development. (Sauer et al, 1994)

Study #5

  • background levels of PCBs are only slightly related to serum concentration of total thyroxine, free thyroxine, and thyroid stimulating hormone at birth
  • studied 160 children
Polychlorinated biphenyls (PCBs) are industrially produced environmentally persistent compounds. In developed countries all humans have detectable levels in blood and other tissues. PCBs alter thyroid hormone metabolism in animal experiments, and human data suggest background-level exposure may have similar effects in neonates. We evaluated this possible effect among 160 North Carolina children whose in utero PCB exposure was estimated on the basis of the mother's PCB levels in milk and blood, in 1978-1982 (estimated median PCB level in milk at birth, 1.8 mg/kg lipid). Their umbilical cord sera were thawed in 1998 and assayed for total thyroxine, free thyroxine, and thyroid stimulating hormone. We found that PCB exposure was not strongly related to any of the thyroid measures. For example, for a one unit change in milk PCB concentration (mg/kg lipid), the associated multivariate-adjusted increase in thyroid stimulating hormone level was 7% (95% confidence limits (CL) = -6, 21). Despite the possibility of sample degradation, these data suggest that within the range of background-level exposure in the United States, in utero PCB exposure is only slightly related to serum concentration of total thyroxine, free thyroxine, and thyroid stimulating hormone at birth. (Longnecker et al, 2000)

Study #6

  • dioxin linked to increased total thyroxine (tT4) --- (certain PCBs are dioxin-like)
  • dioxin linked to increased thyroxine-binding globulin
  • dioxin linked to increased thyrotropin (TSH)
  • studied 38 infants
Animal studies have shown that dioxins influence plasma thyroid hormone concentrations. To investigate the effect of chlorinated dioxins and furans on thyroid hormone concentrations in humans, we studied 38 healthy breast-fed infants. The study population was divided into two groups according to the dioxin concentrations in milk fat of their mothers. Blood samples were taken at birth and at the ages of 1 and 11 weeks. At birth a tendency to higher total thyroxine (tT4) concentrations was found in the high exposure group. At the ages of 1 and 11 weeks the increase of mean tT4 concentrations and tT4/thyroxine-binding globulin ratios in the high exposure group reached significance as compared to the low exposure group. At birth and 1 week after birth, mean thyrotropin (TSH) concentrations were similar in both groups, but at the age of 11 weeks the mean TSH concentrations were significantly higher in the high exposure group. We postulate that the observed plasma tT4 elevation in infants exposed to dioxins before and after birth is the result of an effect on the thyroid hormone regulatory system. (Pluim et al, 1993)

Study #7

  • increased dioxins (& related compounds) correlate with reduced thyroxine (T4) levels (certain PCBs are dioxin-like)
  • mothers and 36 children studied
We investigated PCDDs and related compounds in the blood of young Japanese women, approximately 20 years of age, who had not yet had children, and discussed how the TEQ level of PCDDs and related compounds in their blood may affect the next generation. Means of total TEQ levels were 0.063 pg/g for whole blood basis and 21 pg/g for lipid basis. TEQ of PCDDs, PCDFs and coplanar PCBs accounted for about 43, 34 and 23% of the total TEQ in the whole blood basis, respectively. In the lipid basis, their values were about 44, 34 and 22%, respectively. Previously, we investigated PCDDs and related compounds levels in mother's breast milk, lymphocyte subpopulation and thyroid function of their children, and found negative correlations between the TEQ level of PCDDs and related compounds and CD4+/CD8+, and/or the TEQ level of PCDDs and related compounds and the T4 level in 36 mothers and children. Of these cases, the average age was approximately 28 years. PCDDs and related compounds may be related to immunopathy, such as atopic dermatitis. The effects of PCDDs and related compounds on babies of young Japanese women are important and must be further evaluated. (Iida et al, 1999)

Study #8

  • slight alteration of the thyroid metabolism (still within normal limits) after increased exposure to dioxides and PCB
  • no grounds to advise against breast feeding
As a part of the SGO Health Research Promotion Programme, in collaboration with the Toxicological Research Stimulation Programme, a research programme in the field of toxicology was realized. The study ran from 1990 to 1994 (4 years) and comprised animal and clinical research into the possible adverse effects of exposure of the foetus and the neonate to polychlorobiphenyls (PCBs), polychlorodibenzoparadioxins and polychlorodibenzofurans via the placenta and maternal milk. The clinical studies in neonates revealed a slight alteration of the thyroid metabolism (still within normal limits) after increased exposure to dioxides and PCB (as measured in maternal plasma, cord plasma and maternal milk), while slight neurological abnormalities without clinical relevance were also observed. It is concluded from these study results that there are no grounds to advise against breast feeding. (Petit, 1997)

Study #9

  • no impaired thyroid function, as revealed by plasma levels of TSH and thyroxine
  • studied 12 hospitalized children
It has been shown by others that offspring of mothers who had been exposed to dioxins and polychlorinated biphenyls (PCBs) during pregnancy have elevated plasma levels of thyroid-stimulating hormone (TSH) for at least 3 months after birth and reduced plasma levels of free and total thyroxine during the second week after birth. As elevated levels of dioxins and PCBs can thus alter thyroid hormone status, the relation between the levels of some polychlorinated organic compounds in the blood lipids and growth and thyroid hormone status was studied in 12 hospitalized schoolchildren from the Aral Sea region known to have high exposure to such compounds. Their level of PCBs was two to four times higher than in healthy Stockholm children. Their height was found to be lower than in healthy Swedish children of the same age mean (SDS -0.52) and the body mass index (BMI) was inversely correlated to the total concentrations of PCBs and dichlorodiphenyltrichloroethane (DDT) and its metabolite dichlorophenyldichloroethylene (DDE) in the blood lipids. As the levels of insulin-like growth factor- were reduced to the same extent as the BMI it seems likely that PCBs and DDT cause malnutrition as a result of malabsorption. None of the children had any impairment of thyroid function, as revealed by the plasma levels of TSH and thyroxine. Although the concentrations of beta-hexachlorocyclohexane (beta-HCH) and DDE were extremely high in some of the children there was no relation between thyroid hormone status and the blood lipid levels of PCBs, hexachlorocyclohexane and DDT. However, the concentration of dioxins was not analysed. (Mazhitova et al, 1998)

Study #10

  • serum triiodothyronine (T3) and thyroxine (T4) levels were significantly higher
  • hyperthyroxinemia
  • T4 ratio was significantly higher
  • studied 123 poisoning victims 16 years later
Thyroid function was investigated in 123 yusho patients who were exposed to toxic levels of polychlorinated biphenyls (PCBs) 16 years ago. In yusho patients, compared with the patients without evidence of yusho or normal controls, the serum triiodothyronine (T3) and thyroxine (T4) levels were significantly higher, while thyroid stimulating hormone (TSH) levels measured by sensitive assay were normal. There was no difference in serum levels of albumin, alkaline phosphatase, total cholesterol, and thyroxine binding globulin (TBG) between the two groups and the prevalence of positive antithyroid autoantibodies was almost the same, suggesting that hyperthyroxinemia in yusho patients was not due to increased TBG binding or abnormal autoimmune mechanism. Serum free T4 levels, however, were not elevated, although T4 ratio was significantly higher. The thyroid hormone levels were higher than normal value in 4 of 123 yusho patients but only 1 case had clinical symptoms such as excessive perspiration. Despite (incomplete abstract)  (Murai et al, 1987)

Study #11

  • thyroglobulin antibody in Yusho patients is not frequent and it may be associated with blood PCB concentration
  • 8.6% had elevated TSH levels
  • studied 81 patients, 28 years after accidental PCB poisoning
To evaluate chronic effect of polychlorinated biphenyl (PCB) on thyroid functions, thyroid hormone levels and thyroidal autoantibodies were studied in 81 patients with Yusho in 1996. Serum level of thyroid stimulating hormone (TSH) was elevated in 7 cases (8.6%). All of them showed normal triiodothyronine (T3), thyroxine (T4) and free T4 levels, and regarded as latent hypothyroidism. There were no significant correlations between blood PCB concentrations and TSH levels, T2 levels, T4 levels or free T4 levels. Thyroglobulin antibodies were detected in 8 cases (19.5%) of 41 Yusho patients with high PCB concentration (higher than 3.0 ppb), and in only one case (2.5%) of 40 patients with low PCB concentration (lower than 2.9 ppb). We conclude that thyroglobulin antibody in patients with Yusho is not frequent and it may be associated with blood PCB concentration. (Tsuji et al, 1997)

Study #12

  • increased levels of PCBs, dioxins and furans in breastmilk correlated with decreased thyroxine (T4) and triiodothyronine (T3)
  • background levels of PCBs, dioxins and furans may effect thyroid hormone status in infants
  • studied 36 breast-fed infants
Effects of postnatal exposure to polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and coplanar polychlorinated biphenyls (Co-PCBs) on thyroid hormone status were studied in the peripheral blood of 36 breast-fed Japanese infants. Estimated total intakes of these chemicals in toxic equivalent quantity (TEQ) converted into 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) from the breast milk significantly and negatively correlated with the levels of triiodothyronine (T3) and thyroxine (T4) in the blood of breast-fed babies. Therefore, exposure to background levels of the highly toxic organochlorine chemicals through the breast milk may cause some effects on thyroid hormone status in Japanese infants. (Nagayama et al, 1998)

Study #13

  • enlarged thyroids
  • abstract incomplete --- more effects may have been noted
  • studied 372 women
This review presents the definition of main groups of organic chlorinated pollutants (polychlorinated biphenyls, dibenzodioxines, dibenzofurans, hexachlorobenzene, hexachlorocyclohexane, DDT etc.). Moreover, the similarity of their effects with those of steroid and thyroid hormones either via steroid/thyroid receptor or via specific Ah-receptor is described. Special attention is paid to their effects on the thyroid gland in experimental conditions as well as on professionally and nonprofessionally exposed population. Finally, own preliminary data are presented which were obtained by the examination of 249 employees of the factory Chemko producing polychlorinated biphenyls in 1955-85 as compared with control groups of 218 adults from Moldava, Trebiæsov and Koæsice and 278 women from Orava. In women from Chemko the frequency of thyroid volumes (by ultrasound) over 22,1 ml was 40/202, while that from Moldava was 16/170 (p < 0.001). In the employees of Chemko also significantly higher frequency of thy (incomplete abstract) (Langer et al, 1996)

Study #14

  • no relation between PCB and thyroid hormone or creatine kinase and thyroid hormone was observed
18.9% of the patients with Kanemi Yusho showed an elevation of serum creatine kinase, however, the cause is still unknown. The relation between exercise, dehydration, thyroid hormone and concentration of PCB was studied. Dehydration, hyperexercise and PCB affected the elevation of creatine kinase. No relation between PCB and thyroid hormone or creatine kinase and thyroid hormone was observed. PCB may change the permeability of muscle plasma membrane. (Yoshimura et al, 1997)

Study #15

  • significant differences in thyroxine (T4) and T4-RT3 index, correlated with PCB exposure
  • studied 111 workers, half exposed to PCBs
Thirty-eight transformer repairmen currently exposed to polychlorinated biphenyls (PCBs), 17 former transformer repairmen, and 56 comparison workers not known to be exposed to PCBs were studied. Measurements were made of serum liver function tests, gamma-glutamyl transpeptidase (GGT), lipid profile, thyroid function tests, and other serum biochemistry; hemoglobin; white cell count; 24-hour excretion of delta-aminolevulinic acid, porphyrins, 17-hydroxycorticosteriods and 17-ketosteroids; sperm count; spirometry; and antipyrine half-life to evaluate microsomal mixed function oxidase induction. The total exposed group differed significantly from the comparison group in albumin, LDH, T4, T4-RT3 index, and actual/predicted FEV1. Significant differences among all three exposure groups were seen for albumin, T4, T4-RT3 index, and 17-hydroxycorticosteroid excretion. Differences in FEV1 were attributable to smoking. Significant correlations between serum PCBs and serum lipids were removed by adjustment for co (incomplete abstract) (Emmett et al, 1988)

Study #16

  • thyroid function was normal.
  • studied 182 newborns
To determine whether neonatal neurologic function is adversely affected by seafood contaminants from maternal diet during pregnancy. One hundred eighty-two singleton term births were evaluated in the Faeroe Islands, where marine food includes pilot whale. Maternal serum, hair, and milk and umbilical cord blood were analyzed for contaminants. Levels of essential fatty acids, selenium, and thyroid hormones were determined in cord blood. Each infant's neurologic optimality score was determined at 2 weeks of age adjusted for gestational age, and predictors were assessed by regression analysis. Exposures to methylmercury and polychlorinated biphenyls were increased in relation to maternal seafood intake, as were omega3 fatty acid concentrations in cord serum. Thyroid function was normal. After adjustment for confounders, a 10-fold increase of the cord-blood mercury concentration was associated with a decreased neurologic optimality score of 2.0 (P =. 03). This effect corresponds to a decrease in gestational age of about 3 weeks. Other indicators of the seafood diet had no effect on this outcome. Prenatal exposure to methylmercury from contaminated seafood was associated with an increased risk of neurodevelopmental deficit. Thus in this North Atlantic population, methylmercury constituted an important neurologic risk factor, although effects of other seafood components were not detectable. (Steuerwald et al, 2000)

Study #17

  • thyroid changes occurred, consistent with PCB exposure
  • 2 of 6 workers exposed to PCBs were affected
A walk through survey and medical examinations were conducted to determine exposures to polychlorinated-biphenyls (PCBs) and asbestos at the Babcock Wilcox facility (SIC-3443), Brunswick, Georgia, on May 18, 1982. The evaluation was requested by Boilermakers Union Local 901 for 45 electricians and maintenance workers. Medical examinations were given to 12 employees, 6 of whom had a history of exposure to PCBs. A questionnaire was administered to determine asbestos exposure. Pulmonary function tests were given to eight workers with potential asbestos exposure. For workers with potential PCB exposure, none exhibited typical skin lesions. Blood concentrations of PCB were within normal ranges. In two subjects, thyroid and liver changes occurred that were consistent with PCB exposure. In subjects evaluated for asbestos exposure, four had decreased vital capacity and three of these had chronic bronchitis. Soil samples contained between 4.8 and 110 parts per million PCBs. The authors conclude that it is likely that workers are exposed to soils containing PCBs and there is potential exposure to asbestos at the facility. The authors recommend that transformers be labeled clearly warning about PCBs. Employees with long potential exposure times to PCBs and asbestos should be monitored to determine the cause of the symptoms. (Williams et al, 1983)

Study #18

  • thyroid results not clear (incomplete abstract)
  • studied 224 newborns
Preliminary findings of a cohort study designed to reveal the effect of the in-utero exposure to organochlorines on the health status of Inuit newborns in the Kativik region of Quebec, Canada were presented. Evaluations included birth weight, height, head circumference, and thyroid stimulating hormone blood levels. Breast milk levels were used as an indirect measure of fetal exposure. A total of 224 births occurred between July 1989 and July 1990. Milk analysis was performed for 109 of the mothers. Statistically significant negative associations were found between the height of male Inuit newborns and the concentrations of chlorinated pesticides, polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs). In female newborns, positive associations were found between birth weight and PCBss/PCDFs. In male newborns, the associations remained significant even when controlling for maternal factors such as gestational age. The authors note that the indirect estimation of fetal exposure to contaminants using mother's milk levels is less precise than a direct cord blood measurement even though levels were adjusted on a lipid basis. The authors suggest that studies be made to determine whether these compounds act differently on the intrauterine development of males and females. (Dewailly et al, 1993)

Study #19

  • abstract incomplete
Objective: To evaluate whether long-term exposure to heavy environmental pollution with polychlorinated biphenyls (PCBs) could result in impairment of thyroid status as evaluated by an epidemiological field survey. Methods: Thyroid volume (ThV) was measured by ultrasound in 238 employees of a factory (EMP) which previously produced PCBs and 454 adolescents from the surrounding area polluted by PCBs. Controls (C) were 572 adults and 965 adolescents from much less polluted areas. In the 2 3 8 EMP and various numbers (shown in parentheses) of adult C the levels of thyroid-stimulating hormone (TSH) (n = 498), thyroxine (n = 49 8), thyroglobulin (n = 278) and thyroid antibodies (anti-peroxidase (TPO Ab), n = 517; anti-thyroglobulin (Tg Ab), n = 455; anti-TSH receptor (TSHR Ab), n = 238) were estimated in serum, while only TSH and TPO Ab were measured in 269 and 171 adolescents from polluted and control areas respectively. In several subjects in whom thyroid disease was suspected, total tri-iodothyronine or free t
(abstract incomplete) (Langer et al, 1998)

Study #20

  • more research is needed, to include thyroid status
Half of a cohort of 3683 Michigan residents exposed to polybrominated biphenyls (PBBs) in 1973 and 1974 had 2 serum PBB determinations at a 1- or 2-yr interval. The median decrease in serum PBB levels during both 1- and 2-yr intervals was 1 microgram. The geometric mean serum polychlorinated biphenyl (PCB) level (6.3 microgram/L) exceeded that of PBB (4.1 micrograms/L), although the range of PCB levels (smaller than 1-57 microgram/L) was narrower than that of PBB levels (smaller than 1-3150 micrograms/L). Mean PCB and PBB levels were higher for males, and mean PCB levels increased with age. In a subgroup with higher-than-average PBB levels, serial clinical chemistry tests during 4 different years showed no consistent significant correlation with serum PBB levels. Tests with greater sensitivity and specificity for hepatic microsomal enzyme induction and thyroid status are needed in future evaluations of the most highly exposed subgroup of the cohort. (Kreiss et al, 1982)

Go to 40 Study Reviews linking PCBs and Thyroid Changes

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Thyroid Disorders, Hypothyroidism and Hyperthyroidism