Eating ice

Do you like to eat ice?

Do you feel like you need to eat ice?

Enough to wolf down a tray of ice every day for at least two months?

If you answered yes to that last question, you might want to get your iron level checked. Because apparently iron deficiency is highly correlated with a compulsion to eat ice.

It’s more than highly correlated, actually. Iron deficiency, the most common nutritional deficit in the world, pretty much definitely causes pagophagy. Almost one quarter of iron-deficient people in the US report this craving (and that number has been reported as high as 55% in other studies), and as soon as iron-deficient people start to take supplements, the compulsion goes away. Even before their haemoglobin levels go back to normal.

When your body doesn’t have enough iron, eating ice is a weird thing to do. Ice doesn’t have any iron. And any trace amounts of minerals in ice would be present in water too, but there’s no compulsion for liquid water, just the solid stuff.

So what’s going on?

We don’t really know. The closest I’ve come to an answer is from a decent randomized control trial in 2014, which showed that, in iron-deficient people, eating ice boosted brain processing speeds.

This was the set up: A group of iron-deficient people and a group of normal-iron people were given a series of tests usually used to screen for AD/HD and either some tepid water or some ice to chew. The iron-deficient who got ice massively outperformed the suckers left without their ice fix. Here’s the kicker though: the people with normal iron all did fine on the test whether they had ice or water. And their scores were the same as the ice-eating iron-deficient people.

Iron in the blood is used by red blood cells to carry oxygen around, so if you don’t have enough iron, you won’t have enough oxygen. This leads to fatigue and lethargy, which is why iron-deficient people generally won’t score well on neuropsychological tests. Until they have ice.

The leading theory about why ice might temporarily alleviate fatigue (like a cup of a coffee) is to do with the diving reflex. When a mammal’s face is submerged in water, cold receptors in the nose tell the body to go into submarine mode. Blood vessels in the extremities contract, sending more blood to the heart and brain. The heart rate slows, meaning the heart muscle needs less oxygen, and the spleen contracts, pushing more red blood cells into the system. It’s like your body is in full-on oxygen conservation mode.

The authors of the 2014 study theorize that ice provides a jolt of cold to the mouth, stimulating this diving reflex and forcing more oxygen to the brain. While that sounds reasonable, my problem is that it doesn’t explain why only the iron deficient would get a brain boost from ice.

So pagophagy remains a medical mystery.

Weird.