Does glutamine help against inflammation in the brain?
In people with severe brain injury and in specific forms of brain inflammation, there are preliminary signals that glutamine may play a role. In healthy people, this has not yet been studied.
Taking glutamine as a supplement for brain inflammation is not the same as glutamine appearing as a sign that something is going wrong. That distinction is crucial for the three available studies.
In animal studies and experiments with cells, glutamine reduces brain inflammation caused by lead poisoning. It does so by dampening the activation of inflammation-related genes through a specific biological process. This is promising, but it concerns a very specific cause of brain inflammation, not brain inflammation in general. Whether this effect occurs in people has not yet been tested.
In people with severe traumatic brain injury, researchers looked at a combination of nutrients: glutamine together with omega-3 fatty acids and arginine. That package led to lower measurable inflammation markers and fewer infections in hospital. Death rates were slightly lower and hospital stays shorter, but those differences were not statistically convincing. On top of that, it is impossible to say how much glutamine itself contributed, because it was never given on its own.
A third finding turns things around: in research into damage to the barrier between the blood and the brain, raised glutamine and glutamate levels in the blood turned out to be a sign of brain inflammation, not a remedy for it. High glutamine here points to damage, not recovery. This says nothing about the effect of glutamine supplements, but it does show that glutamine's role in the brain is complex and works both ways.
In short, there are preliminary signs that glutamine may do something in specific forms of brain inflammation, but solid evidence in people is largely absent. If you take glutamine as a healthy person to prevent brain inflammation, there is no research at all that supports that. If you are a patient with brain injury, always discuss nutritional supplements with your treating doctor.
This answer draws on two overview studies that combined many smaller studies, and one combined study involving people, animals, and experiments with cells. The overviews are small: one combined analysis included five studies, and the metabolomics overview included eight studies with large methodological differences. None of the studies tested glutamine on its own in people as a treatment for brain inflammation. The researchers themselves rate the strength of the evidence as limited, partly because of the small number of studies and the considerable variation between them.