Pagophagia—or a compulsive desire to eat ice—is very common in individuals with iron deficiency anemia, across ages and cultures, even in places where ice is a rare commodity.

The roots of this craving have long been unknown, but a new Penn study sheds light on the mystery, showing that eating ice gives people with anemia a mental boost.

The study was conducted by Melissa Hunt, an associate director of clinical training in the Department of Psychology in the School of Arts & Sciences, along with Samuel Belfer and Brittany Atuahene, former undergraduate students in her research experience course.

Pagophagia has been linked to iron deficiency anemia, a condition marked by low levels of hemoglobin, the component of red blood cells that transports oxygen throughout the body. Previous studies have shown that ice cravings go away when iron levels return to normal, but the mechanism responsible for the connection has remained elusive. Earlier hypotheses that suggested ice was a way of soothing inflammation of the tongue have been systematically disproven.

Hunt came up with a new theory after hearing the same story from several people with anemia.

“They said, ‘It’s like a cup of coffee—I don’t feel awake unless I’m chewing ice,’” she says. “That immediately suggested to me there had to be way of measuring an objective neurocognitive variable that ice was impacting for people with anemia.”    

The team began with a survey study that, for the first time, showed pagophagia is much more prevalent among people with anemia than the general population. With this basic connection between the conditions established, the researchers recruited both anemic and healthy people for an experiment that would test their alertness, vigilance, and reaction time.

Watching a computer screen, participants were shown a series of images in rapid succession. Each time, they would see a big square and small square; they were asked to push a button if the small square was on top, and do nothing if it was on the bottom. Participants saw these shapes flash across the screen, about once a second, for 22 minutes—a long time to focus on such a tedious task.          

Before the test, the researchers gave participants either a cup of ice or an equivalent amount of room-temperature water, to control for the factor hydration might play.

The anemic participants who tried this test without first consuming ice had significantly slower and more inconsistent reaction times, akin to people with moderate to severe attention deficit disorder. Those who had ice beforehand, however, performed about as well as healthy participants, who showed no difference whether they were given ice or water.  

“There is a very clear, functional impact on response time and cognitive processing seen only in anemic individuals,” Hunts says. “We think it has to be the case that ice is triggering some response that is getting more blood—and more oxygen—to the brain. The healthy controls have plenty of oxygen, so by getting a little more, they’re not getting any benefit from it.”