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June 15, 2006 -- Early research in mice shows that being fed iron-fortified formula in infancy may increase the risk of developing Parkinson's diseaseParkinson's disease late in life.
In the study, newborn mice exposed to dietary iron levels similar to those found in infant formula showed evidence of Parkinson's-like neurological degeneration as they aged, the researchers say.
The findings fall far short of proving a link between early life dietary exposure to iron and Parkinson's disease.
And the infant formula industry argues the results have no relevance for formula use -- that mice in the study were actually given much higher levels of iron than an infant would receive from their product.
But the researchers say the study should prompt research in humans to determine if a link with Parkinson's exists.
"This is the first animal study that we know of suggesting that a dietary factor in infancy can impact Parkinson's risk later in life," researcher Julie Andersen, PhD, tells WebMD. "Parkinson's disease is the second most prevalent neurondegenerative disease, after Alzheimer's. This is certainly something that deserves a closer look."
Impact of Early Iron Unknown
It is estimated that 1.5 million Americans have Parkinson's disease, a progressively degenerative brain disorder most common in people over age 65. Symptoms include tremors, slowness of movement, rigidity, and difficulty with balance.
Parkinson's patients have been shown to have higher than normal levels of iron in parts of their brains associated with the disease, but the significance of this has not been well understood.
In earlier animal studies, Florida State University researchers found that mice given a Parkinson's-inducing drug developed Parkinson's-like symptoms and brain changes when fed adequate levels of iron. However, iron-restricted mice seemed to have some protection.
Although iron levels increase in the brain with age, dietary exposures very early in life may have the biggest impact on brain iron levels, Andersen says. That may be because passage of iron into the human brain is at its highest during the first year of life.
"This is why we started looking at infant formulas," Andersen says. "Iron is important early in life and having insufficient amounts can result in catastrophic problems, including mental retardation. But we don't know the impact of early exposure after childhood."
Rethinking Iron Exposure
Andersen and colleagues at the California-based Buck Institute agingaging research center fed young mice the equivalent amount of iron that a formula-fed baby would get in his first year of life, according to the study. They then treated the mice with a Parkinson's-inducing drug and followed them as they aged. The researchers found the mice displayed more Parkinson's-like neurological changes in their brains than mice not fed the additional iron.
The study is published in the June issue of the journal Neurobiology of Aging, and it was funded, in part, by a grant from the National institutes of Health.
The average amount of iron in iron-fortified infant formula is much higher than that found in human breast milk. But the iron in breast milk is more easily absorbed. In addition, iron supplementation is generally recommended for breastfed babies to prevent iron deficiency-related developmental problems.
Andersen says it is clear that iron supplementation is needed early in life. But she adds that if studies in humans also suggest early life iron exposure can increase the risk for neurological disease late in life, infant nutritionnutrition experts may need to rethink how much iron babies should get.
"We recognize that this work is in mice, not humans," she says. "We're not saying not to supplement infant formulas with iron but perhaps the levels need to be adjusted."
J. William Langston, MD, of the Parkinson's Institute, says the new research could prove to be a groundbreaking advance in our understanding of this neurological disease.
"We really have very few models to study early exposure to toxins as a risk factor for late-life diseases such as Parkinson's diseaseParkinson's disease," he says.
Formula Makers Respond
In an interview Thursday, a spokeswoman for the infant formula industry says the new study has little relevance for infant feeding.
Mice in the study consumed much more iron than babies get from formula, despite the researchers' claims to the contrary, says Marisa Salcines, of the International Formula Council.
She notes that the American Academy of Pediatrics recommends iron-fortified infant formula for babies that are not exclusively breastfed.
In 1999, the AAP's Committee on Nutrition even raised the minimum recommended level of iron in infant formulas.
"The extremely high doses of iron fed to the mice in this study are at least 60 times as much as consumed in iron-fortified infant formulas on a weight-adjusted basis, and the form of iron is not the iron used in infant formula," she tells WebMD.
"The study by the Buck Institute is an iron study, and not an infant formula study, and it is not relevant to infant feeding," Salcines says. ... "The AAP continues to recommend iron-fortified infant formula as the only safe and nutritious alternative to mother's milk."
SOURCES: Kaur, D. Neurobiology of Aging, June 15, 2006, online edition. Julie K. Andersen, PhD, Buck Institute for Age Research, Novato, Calif.. William Langston, MD, CEO and scientific director, Parkinson's Institute, Sunnyvale, Calif. Levenson, C, "Role of Dietary Iron Restriction in Mouse Model of Parkinson's Disease," Exp Neurol, December 2004; vol 190: pp 506-514. International Formula Council Statement, June 15, 2006. Marisa Salcines, manager of communications, International Formula Council.