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Category: children

Published on Leave a comment on Early Childhood Experiences Key to Preventing Allergies

It's official - the medical community has accepted that a key element in preventing allergies and asthma is early childhood exposure to allergens - whether peanuts, dust, or pets. Instead of avoiding the allergens (which was the medical advice for decades) - getting early exposure to them is key to preventing allergies. Apparently growing up on a farm is best (with exposure to farm dirt and dust), especially a dairy farm with animals and raw milk (a number of studies have found that unprocessed raw milk and its microbes also helps health). But if one doesn't live on a farm, then having furry pets in early childhood is also beneficial in reducing the incidence of allergies. The following study shows that microbes are involved - pet microbes were found in the guts of many of those children who did not develop early allergies! From Medscape:

Furry Pets 'Enrich' Gut Bacteria of Infants at Risk for Allergies

In a small, preliminary study, infants in households with furry pets were found to share some of the animals' gut bacteria - possibly explaining why early animal exposure may protect against some allergies, researchers say. The infants' mothers had a history of allergy, so the babies were at increased risk. It was once thought that pets might be a trigger for allergies in such children, the authors pointed out online September 3 in the Journal of Allergy and Clinical Immunology.

"Earlier it was thought that exposure to pets early in childhood was a risk factor for developing allergic disease," coauthor Dr. Merja Nermes, of the University of Turku in Finland, told Reuters Health by email. "Later epidemiologic studies have given contradictory results and even suggested that early exposure to pets may be protective against allergies, though the mechanisms of this protective effect have remained elusive."Adding pet microbes to the infant intestinal biome may strengthen the immune system, she said.  ...continue reading "Early Childhood Experiences Key to Preventing Allergies"

Published on Leave a comment on Time Spent Outside and Nearsightedness

Another study found that young children who more time spent outside in natural light for 3 years resulted in fewer cases of myopia (near-sightedness). Specifically, the good results were found from one additional 40-minute class of outdoor activities each school day, as well as parents encouraging their children to play outdoors after school hours, especially during weekends and holidays. So....those of you who are parents of children huddled inside - get them outside daily in the sunlight to soak up sunshine for vitamin D and to help their vision. From Science Daily:

Additional time spent outdoors by children results in decreased rate of nearsightedness

The addition of a daily outdoor activity class at school for three years for children in Guangzhou, China, resulted in a reduction in the rate of myopia (nearsightedness, the ability to see close objects more clearly than distant objects), according to a study in the September 15 issue of JAMA.

Myopia has reached epidemic levels in young adults in some urban areas of East and Southeast Asia. In these areas, 80 percent to 90 percent of high school graduates now have myopia. Myopia also appears to be increasing, more slowly, in populations of European and Middle Eastern origin. Currently, there is no effective intervention for preventing onset. Recent studies have suggested that time spent outdoors may prevent the development of myopia, according to background information in the article.

Mingguang He, M.D., Ph.D., of Sun Yat-sen University, Guangzhou, China, and colleagues conducted a study in which children in grade 1 from 12 primary schools in Guangzhou, China (six intervention schools [n = 952 students]; six control schools [n = 951 students], were assigned to 1 additional 40-minute class of outdoor activities, added to each school day, and parents were encouraged to engage their children in outdoor activities after school hours, especially during weekends and holidays (intervention schools); or children and parents continued their usual pattern of activity (control schools). The average age of the children was 6.6 years.

The 3-year cumulative incidence rate of myopia was 30.4 percent (259 cases among 853 eligible participants) in the intervention group and 39.5 percent (287 cases among 726 eligible participants) in the control group. Cumulative change in spherical equivalent refraction (myopic shift) after 3 years was significantly less in the intervention group than in the control group.

"Our study achieved an absolute difference of 9.1 percent in the incidence rate of myopia, representing a 23 percent relative reduction in incident myopia after 3 years, which was less than the anticipated reduction. However, this is clinically important because small children who develop myopia early are most likely to progress to high myopia, which increases the risk of pathological myopia. Thus a delay in the onset of myopia in young children, who tend to have a higher rate of progression, could provide disproportionate long-term eye health benefits," the authors write.

Published on Leave a comment on Viruses Live in The Guts of Healthy Babies

Yes, even healthy newborns have a diversity of viruses in the gut - this is their virome (community of viruses), and it undergoes changes over time. In fact, the entire infant microbiome (community of microbes) is highly dynamic and the composition of bacteria, viruses and bacteriophages changes with age. One interesting finding is that initially newborn babies have a lot of bacteriophages (viruses that infect bacteria), but that these decline over the first two years of age. From Medical Xpress:

Viruses flourish in guts of healthy babies

Bacteria aren't the only nonhuman invaders to colonize the gut shortly after a baby's birth. Viruses also set up house there, according to new research at Washington University School of Medicine in St. Louis. All together, these invisible residents are thought to play important roles in human health.The study, published online Sept. 14 in Nature Medicine, reports data from eight healthy infants and is one of the first surveys of viruses that reside in the intestine. The investigators analyzed stool samples to track how the babies' bacterial gut microbiomes and viromes changed over the first two years of life.

"We are just beginning to understand the interplay between all the different types of life within our gut," said senior author Lori R. Holtz, MD, assistant professor of pediatrics. "They are not stand-alone communities. We also are seeing that the environment of the infant gut is extremely dynamic, which differs from the relative stability that has been shown in adults."The earliest stool samples were taken at 1-4 days of life, and even at this early time point, Holtz noted, viruses were present.  ...continue reading "Viruses Live in The Guts of Healthy Babies"

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Several recent studies have found that constant exposure to high levels of air pollution has negative effects on the brain. The last post described negative effects on the gray matter in brains (resulting in smaller brain volumes) of elderly women from air pollution, but this study found negative effects (lower grade point averages) in young children from high air pollution. From Environmental Health News:

Bad air means lower grade point averages in Texas

Fourth and fifth graders in El Paso, Texas, are more likely to have lower grade point averages if heavily exposed to contaminated air at home, according to a new study.It bolsters a growing body of evidence that air pollution can impair success in school.

They found that for all types of air pollution sources, more exposure corresponded with lower grade point averages. Only one type of pollution—point sources such as factories—was not significantly linked to lower grade point averages.University of Texas at El Paso researchers analyzed the grade point averages of 1,895 children and, using their home location, estimated their exposure to air toxics—such as benzene, arsenic, lead, mercury, hydrochloric acid, toluene, vinyl bromide, xylenes, and diesel particulate matter—using federal data.

“Effects appear to be insidious, since they are mild, unlikely to be perceived, and, hence, unlikely to be addressed in any way … seemingly trivial effects on children’s development may translate into substantial impacts throughout the life course in terms of physical and mental health and personal success,” the authors wrote.The researchers did control for some other things that can affect children’s grades such as poverty, mother’s age, education and ability to speak English, and the child’s race and sex.

Still, the study doesn’t prove that dirty air makes kids do worse in school. It does, however, suggest children’s developing bodies are more susceptible to air pollution, which can harm their respiratory systems and brain.Air pollution might hamper kids’ grades via two primary ways: Illnesses, mostly respiratory, that would make them miss school, and developmental problems resulting from long-term exposure, said Sara Grineski, an associate professor of sociology at The University of Texas at El Paso and co-author of the new study.

Others have found similar links between air pollution and academic performance. Three months ago Columbia University's Perera and colleagues reported that New York City children born to mothers in poverty and exposed to certain air toxics during pregnancy had lower IQs.  Perera, tracking the mothers and children since before birth, said the pollution exposure prior to birth is more strongly linked to learning and behavioral problems. 

In the current study it’s unclear if the children were exposed in their mothers’ womb—an exposure window that is critical to brain development, Perera said....Other studies support this—in February Calderón-Garcidueñas and colleagues reported Mexico City smog was linked to impaired short-term memory and IQ in children.

The city is more than 80 percent Hispanic....Previous studies have shown that El Paso’s minorities are disproportionately impacted by toxics, Grineski said. The city of 675,000 is one of the worst when it comes to particulate matter—a mix of substances emitted by combustion sources, including cars, trucks, industrial plants and wood burning—especially coarse particulates, PM10, those between 2.5 and 10 micrometers (from about 25 to 100 times thinner than a human hair, according to the EPA). El Paso’s 24-hour PM10 average is about 233 micrograms per cubic meter of air, according to the latest EPA data from 2013, which was eighth highest among more than 500 U.S. cities. El Paso, along with Laredo, has the highest carbon monoxide levels in Texas.

Published on Leave a comment on Why Breastfeeding Is So Important

There has been much discussion recently about breastfeeding - why is it so important? Is it really better than formula? The answer is: YES, breastfeeding is the BEST food for the baby, and for a number of reasons. Not only is it nature's perfect food for the baby, but it also helps the development of the baby's microbiome or microbiota (the community of microbes that live within and on humans).

Specifically, breast milk transmits about 700 species of bacteria to the baby - bacteria that are important in developing the baby's microbiota, bacteria that are important for the baby's development and health in many ways (including the immune system). No formula does that. Not even close.

There is obviously much we don't know or understand yet, but finding 700 species in breast milk is a big deal. The most variety was in colostrum (the first milk), but even after 6 months (mature milk) they found hundreds of species of bacteria. What was also interesting was that the bacteria species in the breast milk varied whether the baby was born by vaginal birth, unplanned cesarean, or planned cesarean (this last had a somewhat different bacterial community which persisted through the 6 months of the study).

By the way, in the original study, the authors made a point of saying that the 700 bacteria species are NOT bacterial contaminants, but meant to be there! (for those who want to sterilize and pasteurize everything because they think that all bacteria are bad).

This study is from 2013, but well worth reading. From Science Daily: Breast milk contains more than 700 species of bacteria, Spanish researchers find

Researchers have traced the bacterial microbiota map in breast milk and identified the species of microbes taken from breast milk by infants. The study has revealed a larger microbial diversity than originally thought: more than 700 species. The breast milk received from the mother is one of the factors determining how the bacterial flora will develop in the newborn baby.

A group of Spanish scientists have now used a technique based on massive DNA sequencing to identify the set of bacteria contained within breast milk called microbiome.  Colostrum is the first secretion of the mammary glands after giving birth. In some of the samples taken of this liquid, more than 700 species of these microorganisms were found, which is more than originally expected by experts.

"This is one of the first studies to document such diversity using the pyrosequencing technique (a large scale DNA sequencing determination technique) on colostrum samples on the one hand, and breast milk on the other, the latter being collected after one and six months of breastfeeding," explain the coauthors, María Carmen Collado, researcher at the Institute of Agrochemistry and Food Technology (IATA-CSIC) and Alex Mira, researcher at the Higher Public Health Research Centre (CSISP-GVA).

The most common bacterial genera in the colostrum samples were Weissella, Leuconostoc, Staphylococcus, Streptococcus and Lactococcus. In the fluid developed between the first and sixth month of breastfeeding, bacteria typical of the oral cavity were observed, such as Veillonella, Leptotrichia and Prevotella....The study also reveals that the milk of overweight mothers or those who put on more weight than recommended during pregnancy contains a lesser diversity of species.

The type of labour also affects the microbiome within the breast milk: that of mothers who underwent a planned caesarean is different and not as rich in microorganisms as that of mothers who had a vaginal birth. However, when the caesarean is unplanned (intrapartum), milk composition is very similar to that of mothers who have a vaginal birth.

These results suggest that the hormonal state of the mother at the time of labour also plays a role: "The lack of signals of physiological stress, as well as hormonal signals specific to labour, could influence the microbial composition and diversity of breast milk," state the authors.

And yes, what you eat while breastfeeding has an effect on the breast milk. From Science Daily:  Carotenoid levels in breast milk vary by country, diet

A Purdue University-led analysis of breast milk concludes that levels of health-promoting compounds known as carotenoids differ by country, with the U.S. lagging behind China and Mexico, a reflection of regional dietary habits. Carotenoids are plant pigments that potentially play functional roles in human development and are key sources of vitamin A, an essential component of eye health and the immune system.

The carotenoid content of a woman's breast milk is determined by her consumption of fruits and vegetables such as squash, citrus, sweet potatoes and dark, leafy greens.

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Recently I've seen a number of published studies that found benefits to someone being bilingual or benefits in learning a new language. Some benefits recently found in bilinguals (or the "billngual advantage"): more gray matter in the executive control area of the brain, 4 to 5 year delay in onset of Alzheimer's symptoms, processing of information more efficiently and more easily, and young bilingual children are more likely to think that everything is learned (while monolinguals more likely to think things are innate). From Science Daily:

Bilinguals of two spoken languages have more gray matter than monolinguals

A new study published in the journal Cerebral Cortex suggests people who speak two languages have more gray matter in the executive control region of the brain...Early on, bilingualism was thought to be a disadvantage because the presence of two vocabularies would lead to delayed language development in children. However, it has since been demonstrated that bilingual individuals perform better, compared with monolinguals, on tasks that require attention, inhibition and short-term memory, collectively termed "executive control."

This "bilingual advantage" is believed to come about because of bilinguals' long-term use and management of two spoken languages. But skepticism still remains about whether these advantages are present, as they are not observed in all studies...."Given this concern, we took a different approach and instead compared gray matter volume between adult bilinguals and monolinguals. We reasoned that the experience with two languages and the increased need for cognitive control to use them appropriately would result in brain changes in Spanish-English bilinguals when compared with English-speaking monolinguals. And in fact greater gray matter for bilinguals was observed in frontal and parietal brain regions that are involved in executive control."

Gray matter of the brain has been shown to differ in volume as a function of people's experiences. A prominent finding of this type was a report that London taxi drivers have more gray matter in brain areas involved in spatial navigation.

What about being bilingual leads to these advantages?....The researchers compared gray matter in bilinguals of American Sign Language (ASL) and spoken English with monolingual users of English...."Unlike the findings for the Spanish-English bilinguals, we found no evidence for greater gray matter in the ASL-English bilinguals," Olulade says. "Thus we conclude that the management of two spoken languages in the same modality, rather than simply a larger vocabulary, leads to the differences we observed in the Spanish-English bilinguals."

Science Daily: Bilingualism delays Alzheimer's manifestation by more than four years

The symptoms of Alzheimer disease (AD) manifest themselves about four to five years later in bilinguals as opposed to monolinguals. In bilinguals, the disease onset was estimated at the age of 77, while in monolinguals, this was at the age of 73.

From Science Daily:  Bilingual brains better equipped to process information

Speaking more than one language is good for the brain, according to new research that indicates bilingual speakers process information more efficiently and more easily than those who know a single language. The benefits occur because the bilingual brain is constantly activating both languages and choosing which language to use and which to ignore, said a researcher.

From Science daily:  Bilingualism changes children's beliefs

Most young children are essentialists: They believe that human and animal characteristics are innate. That kind of reasoning can lead them to think that traits like native language and clothing preference are intrinsic rather than acquired. But a new study suggests that certain bilingual kids are more likely to understand that it's what one learns, rather than what one is born with, that makes up a person's psychological attributes.

White and gray matter of the human brain. Credit: Medline Plus, US National Library of Medicine

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Huh - all that talk and research for years about the first born being the smartest and most responsible. Yes...but according to this large study comparing 377,00 high school students from different families, the differences are so small as to be meaningless (1 IQ point!). Researchers looking within-families (studying siblings within families) say that the effects are larger. Depends on who you want to believe. And this study did not look at the siblings later in life - at achievements, etc. From Medical Xpress:

Birth order has no meaningful effect on personality or IQ, massive study reports

For those who believe that birth order influences traits like personality and intelligence, a study of 377,000 high school students offers some good news: Yes, the study found, first-borns do have higher IQs and consistently different personality traits than those born later in the family chronology. However, researchers say, the differences between first-borns and "later-borns" are so small that they have no practical relevance to people's lives. The analysis found - as a previous large-scale study did - that first-borns enjoy a one-IQ-point advantage over later-borns, Damian said. The difference is statistically significant but meaningless, she said.

The analysis also revealed consistent differences in personality traits between first-borns and later-borns - first-borns tended to be more extroverted, agreeable and conscientious, and had less anxiety than later-borns, for example - but those differences were "infinitesimally small," amounting to a correlation of 0.02, Roberts said. "But in terms of personality traits and how you rate them, a 0.02 correlation doesn't get you anything of note. You are not going to be able to see it with the naked eye. You're not going to be able to sit two people down next to each other and see the differences between them.."

The study controlled for potentially confounding factors - such as a family's economic status, the number of children and the relative age of the siblings at the time of the analysis - that might skew the results, Damian said. For example, wealthier families tend to have fewer children than other families, and so have a higher proportion of first-borns who also have access to more resources that may influence their IQ or personality, she said.

Many previous studies of birth order suffered from small sample sizes, Damian said. Many compared children with their siblings - a "within-family" design that some assert is better than comparing children from different families, as the new analysis did.

The team also evaluated a subset of the children in the study - those with exactly two siblings and living with two parents. This allowed the researchers to look for specific differences between first- and second-borns, or second- and third-borns. The findings confirmed those seen in the larger study, with specific differences between the oldest and a second child, and between second and third children. But the magnitude of the differences was, again, "minuscule," Roberts said.

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The key finding in this research (they studied mice, but this process would also happen in humans) is that: the presence of microbes specifically blocks the immune cells responsible for triggering allergies. Once again we see the importance of a healthy and diverse microbiota (the community of microbes within us), and the need to nurture it from birth. Studies have shown the importance of the first year of life in establishing a healthy microbiome and the development of the immune system. A number of studies have shown that the presence of pets or animals (e.g., living on a farm) reduces the incidence of allergies in children.From Science Daily:

Role of microbiota in preventing allergies

The human body is inhabited by billions of symbiotic bacteria, carrying a diversity that is unique to each individual. The microbiota is involved in many mechanisms, including digestion, vitamin synthesis and host defense. It is well established that a loss of bacterial symbionts promotes the development of allergies. Scientists at the Institut Pasteur have succeeded in explaining this phenomenon, and demonstrate how the microbiota acts on the balance of the immune system: the presence of microbes specifically blocks the immune cells responsible for triggering allergies. 

The hygiene hypothesis suggests a link between the decline in infectious diseases and the increase in allergic diseases in industrialized countries. Improvements in hygiene levels necessarily lead to reduced contact with microbes that is paralleled by an increased incidence in allergic and autoimmune diseases, such as type 1 diabetes.

Epidemiological studies have substantiated this hypothesis, by showing that children living in contact with farm animals -- and therefore with more microbial agents -- develop fewer allergies during their lifetime. Conversely, experimental studies have shown that administering antibiotics to mice within the first days of life results in a loss of microbiota, and subsequently, in an increased incidence in allergy.

However, until now, the biological mechanisms underlying this phenomenon remained unclear. In this study published in Science, the team led by Gérard Eberl (head of the Microenvironment and Immunity Unit at the Institut Pasteur) shows that, in mice, symbiotic intestinal microbes act on the immune system by blocking allergic reactions.

Several types of immune response can be generated in order to defend the organism. The presence of bacterial or fungal microbes provokes a response from immune cells known as type 3 cells. These immune cells coordinate the phagocytosis and killing of the microbes. However, in the case of infection by pathogenic agents that are too large to be handled by type 3 cells (such as parasitic worms and certain allergens), the cells that organize the elimination of the pathogen, but also allergic reactions, are known as type 2 cells.

In this study, scientists at the Institut Pasteur have shown that type 3 cells activated during a microbial aggression act directly on type 2 cells and block their activity. Type 2 cells are consequently unable to generate allergic immune responses. This work demonstrates that the microbiota indirectly regulates type 2 immune responses by inducing type 3 cells.

These results explain how an imbalance in microbiota triggers an exaggerated type 2 immune response normally used to fight large parasites, but that also leads to allergic responses....In terms of allergy treatment, a hitherto unexplored therapeutic approach consists therefore in stimulating type 3 cells by mimicking a microbial antigen in order to block allergy-causing type 2 cells.

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There is growing evidence that women around a lot of endocrine disrupting chemicals at home or in jobs such as cleaners, hairdressers and laboratory workers during pregnancy are more likely to have baby boys with a genital defect called hypospadias (a condition where the opening of the urethra is on the underside of the penis rather than at the tip). From Environmental Health News:

Genital defect in baby boys linked to moms’ chemical exposure

Mothers around a lot of endocrine disrupting chemicals at home or in jobs such as cleaners, hairdressers and laboratory workers during pregnancy are more likely to have baby boys with a genital defect, according to a new study in the south of France.The study adds to mounting evidence that fetal exposure to chemicals that mimic people’s natural hormones may cause hypospadias, a condition where the opening of the urethra is on the underside of the penis rather than at the tip.

French researchers examined more than 600 children in the south of France and found that babies exposed to endocrine disrupting chemicals while their genitals were developing were more likely to suffer from hypospadias. Half the boys had hypospadias and half did not. The risk for those exposed was 68 percent higher than the unexposed boys. The researchers ruled out baby boys with known genetic risks for such defects.

The defect, which can be minor or quite severe depending on how far the opening is from the tip, can lead to problems with urination and, later in life, sexual difficulty....It is one of the most common genital defects in baby boys, and most cases require surgery, often done before they reach two years old. In the United States, an estimated five out of 1,000 boys are born annually with hypospadias, while Europe’s rate is slightly less than two out of 1,000.

The researchers estimated the unborn babies’ exposure by looking at their parents’ jobs and where they lived. Working with hormone disrupting chemicals and living in homes near heavy polluters were both linked to more baby boys having the defect. However, the researchers did say a limit of the study was attempting to estimate fetal exposure to such chemicals.Mothers were most likely to have boys with hypospadias if they worked as a cleaner, hairdresser or beautician.  

Some of the endocrine disrupting chemicals linked to the professions involved in the study were bisphenol-A (BPA), phthalates, polychlorinated compounds, alkylphenolic compounds and organic solvents. Most exposures—78 percent—occurred in the window of development when babies’ genitals are forming.... but detergents, pesticides, and cosmetics accounted for 75 percent of the cases,” the authors wrote in the study published in the European Urology journal this month.

Other possible causes of the birth defect include older, obese mothers, and fertility or hormone treatments during pregnancy, according to the U.S. Centers for Disease Control and Prevention.

This wasn’t the first time scientists have found a link between certain chemicals and hypospadias. Mothers in southeast England who were heavily exposed to endocrine disrupting phthalates on the job were about three times as likely to have a baby boy with hypospadias. Phthalates are used in some cosmetics, fragrances, food packaging and PVC plastics.

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Two studies showing detrimental effects on children from pyrethroids in 2 weeks! The June 3 post was about research linking household pyrethroid exposure to ADHD in children and young teens. The second study found that low level childhood exposures to pyrethroid insecticides was linked to lower scores on an IQ test (Wechsler Intelligence Scale for Children - verbal comprehension and working memory) in 6 year old children. The researchers viewed this as evidence that pyrethroid insecticides may "negatively affect neurocognitive development".

Bottom line: even though pyrethroid pesticides are considered safer than many other pesticides, they still can have undesirable effects on humans, especially developing children. To be safe, use least toxic pest control that uses non-toxic, safe "alternative" or "natural" methods rather than just "spraying a chemical". Another possibility is looking for "organic pest control" or"least-toxic Integrated Pest Management" (IPM) that looks to deal with pest problems with non-toxic methods (which may include sealing holes, heat, caulking, trapping, using sticky traps, and even vacuuming up insects). From Science Daily:

Impact of insecticides on the cognitive development of 6-year-old children

Researchers have provided new evidence of neurotoxicity in humans from pyrethroid insecticides, which are found in a wide variety of products and uses. An increase in the urinary levels of two pyrethroid metabolites (3-PBA and cis-DBCA) in children is associated with a significant decrease in their cognitive performances , particularly verbal comprehension and working memory. This study was carried out on nearly 300 mother and child pairs from the PELAGIE cohort (Brittany).

Pyrethroids constitute a family of insecticides widely used in a variety of sectors: agriculture (various crops), veterinary (antiparasitics) and domestic (lice shampoo, mosquito products). Their mode of action involves blocking neurotransmission in insects, leading to paralysis. Because of their efficacy and relative safety for humans and mammals, they have replaced older compounds (organochlorides, organophosphates, carbamate) considered more toxic.

Exposure of children to pyrethroids is common. It is different to adult exposure, due to the closer proximity of children to ground-level dust (which stores pollutants), more frequent hand-to-mouth contact, lice shampoos, etc. In children, pyrethroids are mainly absorbed via the digestive system, but are also absorbed through the skin. They are rapidly metabolised in the liver, and mainly eliminated in the urine as metabolites within 48 hours.

Pregnancy is also an important period of life for the future health of the child. For this reason, the researchers studied the PELAGIE mother-child cohort established between 2002 and 2006, which monitors 3,500 mother-child pairs. This cohort simultaneously considers exposure to pyrethroid insecticides during fetal life and childhood. A total of 287 women, randomly selected from the PELAGIE cohort and contacted successfully on their child's sixth birthday, agreed to participate in this study.

Two psychologists visited them at home. One assessed the child's neurocognitive performances using the WISC scale (verbal comprehension index, VCI, and working memory index, WMI). The other psychologist characterised the family environment and stimuli that might have had a role on the child's intellectual development, collected a urine sample from the child, and collected dust samples. Exposure to pyrethroid insecticides was estimated by measuring levels of five metabolites (3-PBA, 4-F-3-PBA, cis-DCCA, trans-DCCA and cis-DBCA) in urine from the mother (collected between the 6th and 19th weeks of pregnancy) and from the child (collected on his/her 6th birthday).

Results show that an increase in children's urinary levels of two metabolites (3 PBA and cis-DBCA) was associated with a significant decrease in cognitive performances, whereas no association was observed for the other three metabolites (4-F-3-PBA, cis-DCCA and trans-DCCA). With respect to metabolite concentrations during pregnancy, there was no demonstrable association with neurocognitive scores.