Arsenic is poisonous. But scientists are still trying to figure out what it does to us at very low doses.
A research team has found breastfed infants have lower exposure to arsenic than babies who exclusively drink formula.
Kathy Cottingham is a professor of biological sciences at Dartmouth and an author of the paper in the journal Environmental Health Perspectives. She says that they measured arsenic levels in 6-week-old babies and found that for all the babies, the levels were low. But the formula-fed babies had arsenic levels 7.5 times higher than breastfed babies.
"We think that's associated with the fact that some of the arsenic exposure comes from formula powder and that's relatively low, and the rest of the exposure is from the water that's used to mix the formula," she says. "And because our [study] population comes from a group of families that drink private tap water, which can have arsenic concentrations that vary considerably, the babies also have varied exposures from that water."
Homes that are on private wells don't have to meet federal standards for drinking water so their arsenic levels are unregulated.
Why would arsenic show up in infant formula at all?
Cottingham explains that arsenic is a naturally occurring element that's found pretty much everywhere. There are some parts of the U.S., like New Hampshire and Michigan, where arsenic occurs in unusually high concentrations in groundwater.
"And similar things happen with the products that are used to make formula. So anything that's not completely manufactured in the lab is going to have some potential arsenic in it," she says.
In 2012, Cottingham and her colleagues published a study on formula. They found those formulas containing brown rice syrup had high levels of arsenic.
"At the time we did the study, there were baby formulas that were made with organic brown rice syrup and brown rice syrup, and those products had very high levels of arsenic. The companies that make those formulas have since cleaned up the formula, and so the arsenic concentrations are down within the range of the other powders, is our understanding," says Cottingham.
How concerned should parents be?
She says the levels of arsenic in formula are low, so she says it's more important to know the amount of arsenic in your water. If you're on city water, your water has to meet a federal limit of 10 mg/L.
But if you're on a private well, Cottingham says you should have your water tested.
"If I were feeding an infant right now, I'd want to know about the water I was using to mix the formula with; how much arsenic was in there. And I'd want to act accordingly if my arsenic in my water was high."
However, she says previous studies have found that breastfeeding mothers who are drinking private well water with arsenic levels above federal limits did not pass much of it along to their babies.
"The amazing thing is that there's something about human physiology where even if the moms are drinking water in the 100 to 200 mg/L range, what's coming out in breast milk is very low," Cottingham says.
Even though studies show not much of that arsenic is getting into breast milk, high levels of arsenic are still not good for the mom.
Arsenic can cause cancer and a range of other serious health problems. Cottingham says her research group has found that pregnant moms who are exposed to high concentrations of arsenic can give birth to low-weight babies.
But the levels in this study were low.
"Exposure at the levels we're talking about here, we don't know what, if any, health effects there are. That's part of the reason why we are doing this study is to try to figure out what exposures in these different time windows could mean for long-term outcomes for these children."
Avoiding arsenic in baby food
Federal standards limit arsenic in public sources of drinking water but not in food. Cottingham says that parents concerned about the levels of arsenic their children are exposed to should choose foods that are known to be lower in arsenic.
She cautions concerned parents to limit their babies' consumption of rice cereal, which can have higher levels of arsenic than other grains.
"Lots of people have been counseled to use rice cereal as their [baby's] first source of food and for a very small set of babies that's sort of their best option. But for many babies, pureed fruits and vegetables are just as good."
She says oatmeal and other grains are also a good alternative.
The American Academy of Pediatrics recommends serving your baby a wide variety of foods to decrease their exposure to arsenic.
Arsenic recently has been reported to be present in rice. The reports have raised concern in the press and in the literature that exposure to high levels may increase the risk of bladder and lung cancer. It also is noted that the potential effect on the developing brain is unknown.
In response to these concerns, the Food and Drug Administration (FDA) has convened an advisory group to conduct a risk assessment and update recommendations regarding acceptable levels of arsenic in drinking water and in our diets. Currently, the recommendation from the FDA and the Academy is that children eat a wide variety of foods, including other grains such as oats, wheat and barley, which will decrease their exposure to arsenic from rice.
Consumer Reports investigated arsenic in food in 2012. You can learn more here.
*This story has been updated.