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According to a study conducted among people who grew up in the leaded gasoline era, lead exposure in childhood appears to have lasting negative effects on mental health and personality. in adulthood.
Previous studies have identified a link between lead and intelligence, but this study examined changes in personality and mental health resulting from heavy metal exposure.
The results, which will be published on January 23 in JAMA Psychiatry, reveal that the higher the blood lead level at 11 years, the more likely it is to show signs of mental illness and difficult personality traits at age 38.
The link between mental health and lead exposure is modest, according to the study's coauthor, Aaron Reuben, a postgraduate student in clinical psychology at Duke University. But "it's potentially important because it's a modifiable risk factor to which everyone has been exposed at one point, and now some people in certain cities and countries are still exposed," she said. he declared.
In a previous study, Reuben and his colleagues showed that higher levels of lead in childhood were badociated with lower IQ and lower social status in adulthood.
Both sets of results suggest that the "effects of lead can last a very long time, in this case three to four decades," said co-author Jonathan Schaefer, also a graduate student in clinical psychology at Duke. "Exposure to lead decades ago could be detrimental to the mental health of people aged 40 to 50 years."
Since gasoline was treated with high levels of lead from the mid-1960s to the late 1980s, most adults in their thirties, forties, and fifties were exposed while they were children . Lead from the exhaust gases of motor vehicles has been released into the atmosphere and soils. Today, high exposures to lead are rarer and are most common in children who live in older buildings with plumbing and lead paint.
The topics in this study are part of a group of more than 1,000 people born in 1972 and 1973 in Dunedin, New Zealand, at a time when New Zealand's petrol and lead levels were among the highest in the world. They have regularly participated in badessments of physical and mental health at the local Otago University.
The researchers measured blood lead levels – in micrograms per deciliter of blood (μg / dL) – when participants were 11 years old. Today, a blood lead level above 5 μg / dL will trigger additional clinical follow-up in children. At the age of 11, 94% of Dunedin study participants had blood lead levels above this threshold.
"These are historical data from a time when lead levels of this type were considered normal and not dangerous to children, so most of the participants in our study have never received treatment for the toxicity of lead, "said Terrie Moffitt, lead author of the study. Duke's Nannerl O. Keohane University Professor of Psychology and Neuroscience and Psychiatry and Behavioral Sciences.
Duke's research team also evaluated participants' mental health and personality at different times in their lives, most recently at the age of 38. Diagnostic criteria or symptoms badociated with eleven different psychiatric disorders – dependence on alcohol, cannabis, tobacco or hard drugs; Conduct disorder, major depression, generalized anxiety disorder, fears and phobias, obsessive-compulsive disorder, mania and schizophrenia – were used to calculate a single measure of mental health, called psychopathological factor, or "p factor".
The higher the individual's p-factor score, the greater the number and severity of psychiatric symptoms. The effects of lead on mental health, measured by the factor p, are about as strong as those on IQ, explained the co-author, Avshalom Caspi, professor of psychology and neuroscience, Edward M. Arnett in Duke . "If you're worried about the impact of lead exposure on IQ, our study suggests that you should also worry about mental health," Caspi said.
The research team also determined that members exposed to higher levels of lead in children had been described by family members and friends as more difficult adults. Specifically, they found that study members with higher lead exposure were considered more neurotic, less pleasant and less conscientious than their less exposed peers.
These findings confirm personality traits that were previously related to a number of issues, including physical and mental health impairment, reduced job satisfaction, and distressed interpersonal relationships.
"For people who are interested in intervention and prevention, the study suggests that if you intervene with a group of children or young adults exposed to lead you may need to think very long-term care, "said Schaefer.
In the future, the Dunedin study team is investigating whether lead exposure may be related to the development of later diseases such as dementia or cardiovascular disease.
Reuben said the results are also relevant for other developed countries. "When we observe changes that may result from lead exposures in New Zealand, it is very likely that you have seen the same effects in America, Europe, and other countries that used leaded gasoline. at the same levels at the same time. " "
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