Everyone knows that salt restricted diets are helpful for blood pressure, right? Right? As is often the case, the things that “everyone knows” should always be open to more scrutiny. Frankly if it were that easy, why would we not have fixed the blood pressure problem? There is no doubt that there is a link between salt and blood pressure, but the research is only beginning to bring clarity. Ironically my first exposure to these ideas came from the most unlikely place, which is Dr. David A McCarron, MD, FACP – who is a totally main-stream conventional MD. A lecture from Dr. McCarron in Houston brought to light the large body or research that shows that salt moderation is helpful, but salt restriction – especially to the newly recommended 1500 mg per day for high risk individuals – can be harmful. Let’s talk about why:
There is no doubt that high salt intake increases blood pressure – anyone who has had a big night in Texas with salty corn chips, salty salsa and salt-rimmed margaritas can tell you that. The next day after salt-fest your body is puffy, your hands are tight and your blood pressure is higher because your body holds on to a lot more fluid to help dilute all that salt. This is totally natural and you will never hear me make the argument that salt and blood pressure aren’t intimately linked up, but the solution isn’t as simple as taking all the salt out of your diet.
Salt is vital to every cell and tissue in your body simply because sodium is one of the major ions in your blood stream and is used to transport other things across cell membranes, to help information travel through the body and generally in every step of the processes necessary for life. Because it’s so vital, salt levels in your blood stream are tightly regulated because if they change too much your body will die. The primary way you adjust to changing salt intake is through the hormone aldosterone, which rises when sodium levels in your blood stream get too low. When aldosterone rises your body conserves sodium and excretes potassium through your kidneys and urine. So aldosterone causes an increase in blood sodium, which causes an increase in blood pressure. Aldosterone is also produced by your body if your blood pressure gets too low, so even if you have a salt-restricted diet you can end up with higher sodium and higher blood pressure. This is part of the more complicated Renin-Angiotensin-Aldosterone system that helps regulate blood pressure in humans, but obviously there is a strong link between salt and blood pressure.
What I see from this is that there is a sweet spot – a place where there is the right amount of salt. Not too much, not too little. Let’s call it the Goldilocks spot for salt intake. One huge research study (actually a study of other studies, called a meta-analysis) done by the Cochrane Collaboration shows that long-term moderate salt diets can be highly beneficial to blood pressure for both genders and in all ethnic groups studied. They estimate the Goldilocks spot to be about 3 g (or 3,000 mg) per day. This is higher than the currently accepted medical suggestion of 1,500 mg – 2,300 mg per day.
Medically we also use this same pathway to try to artificially control blood pressure. Two of the main classes of drugs that are used to lower blood pressure are designed to inhibit the release of aldosterone. One class are ACE inhibitors, including captopril, enalapril, lisinopril and ramipril. The other class is called Angiotensin Receptor Blockers, or ARBs and these include losartan, valsartan, telmisartan, irbesartan, and olmesartan. This may mean a severely salt restricted diet could actually make some of the medications you may be taking for blood pressure less effective.
To add ammunition to this argument, the second paper in a series of long-term research about dietary salt intake and risk of death from major cardiovascular events was published. This paper, called the PURE paper was published in the New England Journal of Medicine, and it supports the idea that too high and too low sodium intake are both a problem. This study shows that the group of people with the highest sodium excretion (meaning also the highest intake) at 7 g per day have a 15% increased risk of death from cardiovascular events as compared to average. It also showed that the lowest sodium intake group, below 3 g per day (that’s the Goldilocks spot from the Cochrane study) had a 27% greater risk for death from cardiovascular events. So in this study the lowest salt intake group is at significantly greater risk of dying from heart disease than the highest salt intake group. This means that if you follow the current medical guidelines of 1.5-2.3 grams of salt per day you are actually at higher risk than if you don’t restrict salt at all and have a high-salt diet. Eek!
In this study the lowest salt intake group is more likely to die from heart disease than the highest salt intake group, and following the current medical recommendations would put you solidly into the lowest salt intake (and highest risk) group. This means too little salt as well as too much salt is detrimental to blood pressure control.
As with everything else, it seems the best course of action lies in moderation. Dr. McCarron’s view on the problem was that restricting salt intake can be as harmful as overdoing salt intake, so maintaining a “normal” intake is best. In this, I have to admit, I agree!