I have to say I feel vindicated today reading the result of a meta-analysis (that's a study that studies the overall impact of a group of studies on the same subject) about SALT intake. How many times have my patients and I had discussions about the use of salt in the diet? Feels like thousands! And how many times have patients had the look of incredulousness on their faces when I've told them that there is no evidence for average salt intake to have devastating effects? Thousands! (OK, well that number is not scientifically recorded anywhere, but you get my meaning!)
The meta-analysis was just published in the Evidence Based Medicine Journal (EBM 19(1):33-34, 2014). It's findings?
Blood pressure is reduced by 3mm Hg if you have a lower sodium intake than 2000mg per day. (Keep in mind that in hypertension, the reduction required is 20-30 mm Hg, and that the average reduction in blood pressure by learning deep breathing is more like 15mmHg)
You do have an increased risk of stroke with a sodium intake greater than 2000mg/day. For example, the average risk of stroke in women between 55 and 85 years of age is 6.5 per 100 people per 10 years. So, 19.5 women will have a stroke per hundred over the 30 year time span. With more sodium, this risk was on average, increased by a factor of 24%. That means that approximately 25 our of 100 women will have a stroke instead of 19.5 out of a hundred.
"However, there was no significant association between sodium intake and all-cause mortality, all CVD, or all coronary heart disease events. The significant association with fatal coronary heart disease events was reported based on three observational studies, two from very high-sodium populations and one from an overweight subset. No associations were seen on lower sodium intake with changes in blood lipids (like cholesterol), catecholamine levels (these are stress neurotransmitters) or renal (kidney) function in adults."
So what is the missing information here? There is absolutely no data about fluid intake relative to salt intake in these studies. When you are at biggest risk for a stroke, it is often because the blood is prone to forming clots. Why does it form clots? Because the red blood cells are sticking together when they're not supposed to. Why are they sticking? Probably because the fluid balance of the circulation is not ideal, and/or there is too much inflammation present in the body triggering the clotting response. Think you might use aspirin under these circumstances? Think again-- new guidelines show that "Multiple studies and meta-analyses indicate that there is no specific population in which the benefits of low-dose aspirin therapy for primary prevention exceed the risks." J Am Board Fam Med.; 2014;27(1):78-86. (That is a rant for another day!!)
It's been my professional opinion and observation that adequate salt intake accompanied by appropriate water intake is absolutely essential to health. You are one big salt water jug -- nervous system, muscle tissue, blood, lymph and and digestive juices -- all just salty fluids moving around. You move salt from one compartment to another, and water follows by osmotic pressure. So the composition of fluids is of course related to adequate amounts of both salt and water. An imbalance between salt and water, though, now THAT is of significant concern, and it may well be the missing factor here. Maybe it isn't really sodium by itself at all, and that's why the data doesn't support that out-dated hypothesis. Maybe it is the BALANCE that is key. So my recommendation? Use a biologically appropriate form of salt -- unrefined sea salt is pretty much identical to blood plasma constituents. And drink enough water to have good water turnover - about a third of your body weight in pounds in ounces of water (so 150 lb., 50 oz. water).