Researchers from Dartmouth College in Hanover, New Hampshire, have just presented another reason why breastfeeding is so beneficial to babies: it lowers babies’ exposure to arsenic, a toxic chemical associated with fetal death, low birth weight, and impaired cognitive function. Numerous studies indicate that, where arsenic levels are naturally high, breastfed babies have a relatively low level of arsenic in their urine. Formula-fed babies in these same areas exhibit higher urinary levels of the chemical.

Arsenic is a chemical element (atomic number 33, symbol As) known since ancient times to be toxic. It has been linked to diseases throughout the human lifespan that include cancer and gastrointestinal disorders.

Arsenic is a naturally occurring element in air, rocks, soil, and water. Plants and animals that consume arsenic-tainted water and feed on foods grown in arsenic-rich soil pass their exposure along to other animals, including humans, that eat these plants and animals.

Well water is a common natural source of arsenic exposure in the United States but the chemical is widely used in the pork and poultry industries to prevent disease and induce rapid weight gain. Industrial-scale farmers use the toxin to control infestations of fungi, bacteria, insects, and rodents.

In the human food supply, arsenic levels are usually highest in rice but other crops that also require great quantities of water have high levels of the chemical, too. Apple and grape juice, leafy green vegetables, and seafood are some foods most likely to contain arsenic.

Coal-fired power plants and landfills holding arsenic-treated lumber are two major sources for arsenic exposure in the air and soil.

Professor Kathryn Cottingham, of the Children’s Environmental Health and Diseases Prevention Research Center at Dartmouth, tested arsenic levels from various sources across the state:

  • The tap water supply in 874 households was tested; some used well water as their primary source of water and others used water from a public supply.
  • Urine from 72 six-week-old babies.
  • Breast milk from 9 mothers, aged 18 to 45.

Cottingham’s research team discovered relatively low levels of arsenic contamination overall but:

  • Urinary arsenic levels in babies fed exclusively on formula were 7.5 times higher than babies breastfed exclusively.
  • Arsenic intake/consumption was 5.5 times higher in babies fed only on formula.

The research team discovered arsenic in powdered baby formula as well as in the tap water used to liquify it for consumption. The more formula a baby consumed, the higher its level of urinary arsenic. The researchers suggest the formula “may be the primary source of exposure” for formula-fed infants, “specifically, formula powder accounted for 71% of median estimated exposure” for the infants in the study.

The researchers noted an interesting sequence of events in the urinary arsenic levels of babies fed with formula some of the time and breast milk at other times. The babies’ urinary arsenic levels changed within minutes of feeding, with higher concentrations of the chemical following a formula feeding and dropping within minutes of breastfeeding.


  1. Cottingham, Kathryn L., et al. "Estimated Exposure to Arsenic in Breastfed and Formula-Fed Infants in a United States Cohort (.pdf)." EHP / Environmental Health Perspectives. National Institute of Environmental Health Sciences, 15 Feb. 2015. Web. 10 Mar. 2015.
  2. "Arsenic Toxicity / Who is at Risk of Overexposure to Arsenic?" ATSDR / Agency for Toxic Substances & Disease Registry: Environmental Health and Medicine Education. US Centers for Disease Control and Prevention, 15 Jan. 2010. Web. 10 Mar. 2015.