Lower sodium levels linked to higher brain excitability, study finds

A new study, published in the journal Scientific Reports, has revealed that even small fluctuations in blood sodium levels, within the established healthy range, can significantly impact brain activity.

The research investigated 42 healthy adults, aged 18 to 30, to understand the connection between blood electrolytes and cortical excitability. The findings established a strong link: subjects with lower sodium concentrations exhibited higher cortical excitability, meaning their brains were more reactive to electrical impulses.

This discovery challenges the long-held assumption that variations within the “normal” range are insignificant. The human brain’s function relies on a precise “electrolyte homeostasis,” a delicate balance of charged ions (particularly sodium, calcium, and potassium) essential for generating the electrical signals that govern thought and movement. While severe imbalances (like hyponatremia) are already known to trigger conditions such as seizures, this study highlights the importance of minor variations.

To investigate this, researchers measured the plasma concentrations of various electrolytes and evaluated cortical excitability using Transcranial Magnetic Stimulation (TMS), a non-invasive technique that stimulates the brain with magnetic fields.

The team calculated the “Resting Motor Threshold” (RMT), which is the minimum stimulation intensity needed to cause a muscle in the hand to twitch. They discovered a significant positive correlation: lower sodium levels were linked to lower RMT values, indicating increased excitability.

Key Findings

Sodium showed no significant associations with chloride, potassium, calcium, or phosphate. This link was robust, persisting after age and sex adjustments. All participants’ sodium levels were within the standard clinical range (136–143 mmol/L).

The authors hypothesize that lower extracellular sodium may subtly change how nerve cells conduct electricity. While the current data shows an association rather than a direct cause, the findings suggest that the precise ionic composition of human blood is related to stable neurobiological characteristics.

Future research aims to investigate whether directly adjusting sodium levels can modify brain excitability. This has the potential to advance our understanding of neurological conditions, as well as the processes of memory and learning.