The finding raises the tantalising possibility that preventing this accumulation could be a way to fight the addiction, for which there is currently no medical treatment.
The research, led by Karen Ersche from the University of Cambridge, saw 41 chronic cocaine users and 43 healthy non-users submit themselves to a magnetic resonance brain scan. The team then compared the levels of iron by analysing differences in the brains’ magnetic properties.
In cocaine addicts, iron had accumulated in the globus pallidus, a structure nestled deep in each of the brain hemispheres. The globus pallidus is implicated in habit formation and acts as a “brake” on repetitive behaviours. Damage it and obsessive-compulsive disorder can result.
The amount of iron was directly related to the length of cocaine use – the longer the person had used the drug, the greater the iron stockpile. This could make the mineral an important biological marker for assessing cocaine addiction.
Iron accumulation in the brain went hand-in-hand with mild iron deficiency in the rest of the body, suggesting that iron regulation in general is out of whack in chronic cocaine users.
Given iron’s important biological roles – without it, red blood cells can’t ferry oxygen around the body, for instance – its metabolism is usually tightly regulated, says Ersche. “Long-term cocaine use, however, seems to disrupt this regulation, which may cause significant harm.”
Too little iron in the blood means organs and tissues become starved of oxygen. On the flipside, too much iron in the brain can lead to cell death and neurodegeneration.
The researchers are yet to figure out what causes the iron to accumulate in the brain of cocaine users. One possibility is that cocaine damages the delicate blood-brain-barrier that polices what substances reach the brain. But inflammation in the rest of the body could also play a role.
The researchers also have their eye set on ways to slow down or reverse the iron imbalances, which could ultimately help to wean users off the addictive drug.
Dyani Lewis is a freelance science journalist based in Melbourne, Australia.