What's the science?
A diet high in salt has been linked to altered brain blood supply, stroke and cognitive impairment. Evidence suggests that the immune system becomes activated in response to salt, and may be involved. Recently in Nature Neuroscience, Faraco and colleagues report a mechanism linking salt in the gut to immune system activation and reduced blood flow in the brain.
How did they do it?
They fed mice high salt diets and measured immune system markers in the blood and the function of cells lining brain blood vessels (endothelial cells which work to allow blood flow) at set time intervals over a 24 week period. They also measured resting brain blood flow using magnetic resonance imaging (MRI) with arterial spin labelling.
What did they find?
Mice fed a high salt diet had lower brain blood flow and dysfunctional endothelial cells. Additionally, they had worsened memory function, and a reduced ability to perform daily activities. Mice fed a high salt diet also had higher levels of immune cells (lymphocytes) in the gut, which resulted in higher inflammatory markers (IL-17) in the blood. Importantly, the lowered brain blood flow and cognitive problems were dependent on this immune system response.
What's the impact?
This study confirms previous theories that the immune system plays a role in linking dietary salt with brain function. Importantly, it reveals a specific immune system pathway linking the gut and the brain. This gut-brain pathway could be targeted with therapies to prevent harmful effects of salt on the brain.
G. Faraco et al., Dietary salt promotes neurovascular and cognitive dysfunction through a gut-initiated TH17 response. Nat. Neurosci. (2018)