Salt 4- Sympthetic nervous system

We've previously discussed the function of the autonomic nervous system (ANS).  The ANS is fundamentally divided into the sympathetic (fight or flight) and parasympathetic (rest and digest) divisions.  As a general rule, our body is predisposed toward sympathetic dominance when we don't take care of ourselves.  In other words, when you don't eat/sleep/exercise well & carry too much stress, your body tends to become imbalanced in this department and drive toward overexpression of the sympathetic nervous system.

For example, your blood pressure tends to go up.  Your heart rate tends to go up.  Your ability to digest food goes down.  You respiration rate tends to go up.  All of these are associated and caused by the sympathetic nervous system.

As mentioned, Americans consume way too much salt.  It appears that salt drives the sympathetic nervous system towards overactivity.  A paper from the University of Texas states,

"In recent years, studies have shown that SNA (sympathetic nervous activity) can rise as a result of both acute and chronic increases of body fluid osmolality. These findings have raised the possibility that salt-sensitive cardiovascular diseases could result, at least in part, from direct osmosensory activation of CNS sympathetic drive"   J Phys 2010 Sep 15(Pt18) ;588:3375-84

Much of our brain (in its well state) is dedicated toward suppressing this sympathetic drive.  In other words, it keeps the sympathetics in check.  With excessive salt intake, we predispose toward this heightened sympathetic condition.  Remember that as you cook your dinner tonight.

Salt 3- Why we need it

Without sodium, you would die.  All cells in the body have electrical properties.  Some cells actually depend very heavily on these electrical properties in order to function appropriately.  Whenever a brain cell activates, it depends on a precise balance of sodium rushing into a cell and eventually being pumped back out.  Oddly enough, when sodium rushes into a bunch of cells in a coordinated pattern, our brain is allowed to function as it should. The same thing holds true for muscles.  Without sodium, your muscles would never have an opportunity to contract.

Sodium needs to be in a certain concentration in the blood and around your cells.  "Concentration" refers to how much sodium is present in a given volume of fluid.  For example, let's take 1 teaspoon of sodium and put it in 1 liter of water.  It will taste somewhat salty.  But if I double the amount of sodium and add 2 teaspoons, it will taste more salty because there is more sodium per any given drop of water.  This is more concentrated.

If we now take 3 teaspoons of salt and put it in 50 liters of water, we may not even taste it!  While there is more sodium, it is far less concentrated in the solution.

If we begin to mess around with sodium concentrations, then bad things will happen.  Several years ago, a woman lost her life because she diluted the sodium in her body with way too much water. She drank way too much water and experienced something called hyponatremia.  When this happened, sodium was not able to dance in and out of cells as it normally would and cells began to shut down.

Clearly, sodium is necessary to life.  But as we know, if "a drop is good", it is not necessarily true that "a cup is better."  More is not better.  Balance is necessary.

From this foundational understanding of sodium's behavior in human physiology, we can begin to explore the problems with high sodium in our diets.

Salt 2- Confusion

There was a great piece published in TIME magazine this week regarding salt.  It discussed a controversial study that suggested that sodium reduction may not be as important as once thought.  The piece in TIME also referenced a boldly written article in Scientific American titled, "It's Time to End the War on Salt: the zealous drive by politicians to limit our salt intake has little basis in science"

There's quite a bit of confusion and as discussed in the articles referenced above, there are many scientific papers that ping-pong back and forth debating the influence of salt on overall health.  Nearly all of these studies look at salt's influence on hypertension; a very well-described risk factor for cardiovascular disease.

If you read enough of these types of stories, you realize that ultimately, the conclusion is, "We don't know enough.  We have some ideas but need further research to see what bears out."  The interpreted message for some is, "Therefore, we will eat as much salt as we want since science can't prove that salt is bad."

I hate to 'cut and paste' but this last paragraph from the TIME piece is great:

In the end then, there may be no simple answers. Researchers and public health officials who support population-wide efforts to curb sodium intake have a vast body of evidence to support their point of view. For decades now, they can say, we have seen studies that suggest — but, yes, they only suggest — that salt is deadly. And those who don't support efforts to curb salt consumption can claim, often correctly, that the evidence against salt is merely suggestive.

In other words, you can interpret this particular body of science to support your views and frankly, no one can prove you wrong at this point.  While the policy wonks can have a field day debating both sides of this, where does that leave the average consumer?

So as a person who advocates for the average consumer (I am not a policy maker and have no relationship to any food companies), I'll tell you that frankly, you should eat less salt.  There is enough evidence from a physiological perspective that tells us that too much salt is bad.  Bad enough to kill you?  Maybe not- in and of itself. But certainly bad enough to contribute to several vicious cycles of physiological demise that can be very difficult to break.  

We'll explore.  But the science combined with a healthy dose of common sense will show us that we take in too much salt and that is bad. 

Salt 1- Easy Does It

Everyone has heard the concerns over salt. The health community has generally recommended that daily salt intake be restricted to 1500mg.   This is enough to cover all of our basic needs for sodium. The USDA states that even if we exceed that amount, we really should not go any higher than 2300mg daily (tolerable upper limit);  this is about 1 teaspoon of salt.   The average American consumes 3,436 mg of salt a day with the vast majority consumed through processed foods or restaurant foods. 

To give you some sense of what these numbers mean:

• 1 Big Mac and medium fries alone contain 1310 mg of sodium.
• Two slices of Pizza Hut's pepperoni pizza have 1220 mg
• 6 inch turkey sandwich at Subway has 810mg of sodium.
• One Footlong Italian Sub at Subway has a whopping 3,440 mg of sodium!   That's more than twice the sodium we need in an entire day! 

It's probably an understatement to say the American's consume too much salt.  In fact, the Centers for Disease Control estimates that thousands of lives could be saved each year if we simply cut down our salt consumption.

In the next few posts, we'll take a look at salt and whether there's enough evidence to scare us away from that shaker.