Low, high manganese levels may affect the infant brain

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 2 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 email.

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 1 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 3. 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.