A new study suggests that the female hormones estrogen and estradiol may protect the brain against the toxic effects of lead. It found that young boys with higher levels of lead in their blood performed worse on cognition tests than those with lower levels, while this was not the case for girls, who appeared hardly affected by the chemical element.

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In a group of young children with higher blood levels of lead, boys performed worse than girls on tests of memory, attention and reading readiness.

The study - which is published in the Journal of Environmental Health - is the work of Maya Khanna, a psychology professor in the College of Arts and Sciences at Creighton University in Omaha, NE.

Estrogen is an umbrella term for a large class of female sex hormones, the most well-known being estrone, estradiol and estriol.

Estrogens are essential for growth and development of female secondary sexual characteristics, such as breasts and pubic hair, as well as development and regulation of the menstrual cycle and the reproductive system.

Estrogens are also important for bone formation, and estrogen receptors - proteins on cell membranes that respond to the hormones - are found nearly everywhere in the human body, including the brain.

Study enrolled children from the largest lead clean-up area in the US

For the study, Prof. Khanna enrolled 40 young children aged 3-6 years who were living within an area of Omaha that is designated by the Environmental Protection Agency (EPA) as a Lead Superfund Site.

The lead pollution at the Omaha site is the result of a lead refinery that was operational from the 1870s to the late 1990s. It is now the largest lead clean-up area in the US. EPA figures show the area of impact extends to 27 square miles and is home to nearly 126,000 people, including more than 14,000 children under the age of 7.

When it was operational, the Omaha lead-refining plant emitted lead and other heavy metals into the atmosphere. These were then transported downwind in various directions and deposited on the ground surface. Today, the pollutants can be found in surface soils at residential properties, child care facilities, schools and other residential-type properties, note the EPA.

Another source of lead pollution is lead-based paint, which can still be found on the walls of many old houses in the area.

Prof. Khanna notes that 23 of the 40 children had blood lead levels equal to or higher than 10 micrograms per deciliter (µg/dL), and 17 did not. The children all completed tests of executive function - including memory and attention - and reading readiness.

Of those with high lead levels, boys' cognitive results were worse than girls'

The results showed that of the children with higher blood levels of lead, the boys performed worse than the girls on executive function tests. However, this effect was not so pronounced in the reading readiness tests.

The study is thought to be the first to show that lead can affect the cognitive development of even very young children and that the consequences appear to be worse for boys than girls.

Prof. Khanna says the study reinforces previous findings that suggest estrogen and estradiol in females may protect the brain against the negative effect of neurotoxins. He adds:

"The findings also add to the evidence that lead exposure has a negative impact on cognitive functioning, especially those functions housed within frontal areas of the brain. Executive functions are controlled largely by the prefrontal cortex, while reading skills rely more heavily on the temporal or parietal areas of the cerebral cortex."

According to the Centers for Disease Control and Prevention (CDC), at least 4 million US households have children living in them that are being exposed to high levels of lead.

The CDC note that among children aged 1-5, there are around half a million with blood lead levels above 5 µg/dL, the reference level at which they recommend public health actions be initiated.

In August 2014, Medical News Today learned how in a study of mice, researchers at the University of Michigan discovered that fetal exposure to lead may be linked to obesity. Specifically, they found male mice exposed to lead while in the womb had an 8-10% increase in weight.