Babies with either relatively high or relatively low levels of manganese in their blood may be slower to hit certain developmental milestones in their first year than other infants, a new study suggests.
The findings do not prove that manganese — which is present in food, water, air and soil — is the reason for the slower development. But they are in line with the general understanding of manganese — that small amounts in the diet are necessary for normal nervous system function, while high amounts can be harmful.
What's new in this study is that it focused on manganese levels in the first few years of life, and whether there might be any effects of relatively low-level environmental exposure on the still-developing brain.
Most of what's been known about the health effects of elevated manganese levels has come from studies of workers heavily exposed to the element on the job, explained lead researcher Dr. Birgit Claus Henn, of the Harvard School of Public Health in Boston.
In their study, Henn and her colleagues found that at the age of 12 months, children in either the bottom 20 percent or the top 20 percent for blood manganese levels had lower scores on a standard test of mental development than those whose manganese levels fell in between.
On the other hand, blood manganese at age two was not related to mental development scores. And while there was still a relationship between manganese levels at age 12 months and mental-development scores at older ages, the connection was weaker, the researchers report in the journal Epidemiology.
Because the study is the first to look at blood manganese levels and brain development in children this age, the findings should be "interpreted cautiously," Henn told Reuters Health in an e-mail.
However, she said, "if our findings are confirmed in other studies, the results suggest that both low and high manganese levels may have adverse effects on neurodevelopment among young children, especially at one year of age, which may be a sensitive time point."
Manganese is a natural component of rock and soil, and people are routinely exposed to it through air, water and food, including grains, fruits and vegetables. It is also used in industry, mainly in steel production, and heavy occupational exposure to manganese can be toxic to nerve cells — leading to symptoms such as difficulty concentrating and Parkinson-like problems like slowed movement and coordination problems.
For the current study, Henn and her colleagues followed 448 Mexican children from birth to age three. Every six months, the children were given standard tests of mental development, including measures of vocalization and communication, memory and problem-solving — such as tackling simple goals like reaching a toy.
In general, children in the bottom and top 20 percent for blood manganese at the age of 12 months scored about three points lower than their peers on the mental development.
According to Henn, that difference is akin to what has been seen when young children's blood levels of lead — which is known to harm early brain development — rise from 10 micrograms per deciliter of blood (mcg/dL) to 30 mcg/dL (Lead levels of 10 mcg/dL or higher are considered to be potentially dangerous in young children).
According to U.S. health officials, the "normal" range of manganese levels in the blood is between four and 14 micrograms per liter (mcg/L) of blood. However, that range is not age-specific, Henn and her colleagues point out, and there is currently no clear "normal" for young children.
In this study, children in the bottom 20 percent for manganese at the age of 12 months had levels below roughly 20 mcg/L. In the top 20 percent, levels were higher than 28 mcg/L.
It is not certain that the manganese levels themselves were responsible for the relatively lower mental-development scores. The researchers did account for a number of other factors — including blood lead levels and mothers' IQ and education levels — and the connection remained.
However, Henn said that it is still possible that other factors, such as exposures to other environmental toxins, could explain the findings.
For now, she said, there are some steps parents can take to limit young children's exposure to manganese while ensuring that they also get enough of it. Manganese is present in some fertilizers and fungicides, for instance, so parents can try to limit their children's exposure to those products.
Henn also noted that while manganese levels in public drinking water are regulated, there can be high levels in well water. So avoiding that water source may be helpful.
On the other hand, Henn said, it is rare for people to be overexposed to manganese through food. So parents should make sure that their children get the healthful foods — including whole grains and green, leafy vegetables — that contain manganese.