Dr. Bernhard Juurlink comments on salt intake, sodium levels in the brain, and blood- brain barrier implications.

I asked Dr. Juurlink to comment on the premise behind this study that sodium levels are elevated in persons with MS (see link below). Here is his response:

"This comes from old observations that Na levels are increased in the brains of people with MS )e.g., Inglese et al. 2010. Brain tissue sodium concentration in multiple sclerosis: a sodium imaging study at 3 tesla. Brain 133(3): 847-857). For example in control white matter Na+ is typically 20 mM and control grey matter Na+ is typically 30 mM whilst in the MS patients it is 25 mM and 35 mM respectively. The thinking generally is that the cellular Na levels are raised but there is an alternative explanation and it comes from a consideration on the differences between intracellular and extracellular sodium concentrations. Intracellular Na+ typically is around 15 mM whilst extracellular Na+ typically is 145 mM. The proportion that extracellular space contributes to brain volume is estimated to be somewhere between 15 and 25%, depending upon the techniques used . The extracellular space would be greater in grey matter compared to white matter because of the increase in the number of small processes/unit volume. Hence, we would expect "tissue" (i.e., cellular plus extracellular) Na+ concentration to be greater in grey matter than white matter. If there is a leakiness of the blood-brain barrier(BBB) one would expect an increase in the relative volume of the extracellular space to the cellular space and one would expect an increase in "tissue" Na+. So, I am not sure what the significance of increased "tissue" Na+ levels is.

Regarding dietary Na intake. If there is an increase in Na intake, this stimulates the kidney to excrete the excess Na. If the kidney does not do this, the increased Na will increase fluid retention, one consequence of this is a greater total blood volume that is associated with an increase in blood pressure - and if one has a leaky BBB, then more fluid moves into the brain from the blood.* The increased excretion of Na lowers blood volume and thereby blood pressure. However, if there is a problem with the regulation of renin secretion (a major cause of hypertension in many people), then we can end up with a double whammy - increased blood pressure because of increased blood volume to increased Na intake and increased blood pressure because of increased renin secretion.

*The normal response of the kidney is to decrease secretion of renin - renin ultimately promotes the formation of angiotensin II. Angiotensin II has a number of actions, one of which to increase the synthesis (and thus release) of aldosterone that acts on the kidney to increase Na uptake (which promotes K loss). The other major action and angiotensin II is to constrict vascular smooth muscle and thereby increase blood pressure."

Note: Dr. Juurlink added that he uses a salt that is half NaCl and half KCl. As always, you can reach Dr. Juurlink with your comments or questions at bernhard@nationalccsvisociety. org

~Sandra

http://neurology.org/content/82/10_Supplement/P6.150.short


Sodium Intake Is Associated With Increased Disease Activity In Multiple Sclerosis (P6.150)
neurology.org
To investigate the relationship between salt consumption and clinical and radiological disease activity in Multiple Sclerosis (MS).