Hi folks! Today I want to spend a little, and by little I mean a ton, of time on something that gets a lot of bad press and causes increases in blood pressure, some of it from merely speaking about it…SALT!
If you live in the USA or any other modernized western country you’ve heard the mantra over and over that we need to reduce our sodium intake. This is what was preached at the podiums of pharmacy school during my 4 years. It is still preached and probably will be for quite some time. Today I want to challenge a notion or two about sodium.
First I want to start with a biology lesson. For those of you reading who have little to no background in biological functions, don’t worry, I will sum it up at the end.
Our bodies maintain sodium levels within a tight range. Generally it ranges from 135-145 mEq/L, so the average is about 140. Sodium is an element absolutely required for life. Nerve transmission would not be possible without sodium and potassium gradients. It also helps in regulation of cellular water content and a host of other things. So what happens when your sodium gets too high or too low?
Our water volume as well as our sodium concentrations are both always being adjusted to maintain a level which is beneficial to living. Too high or too low can cause problems. Our hypothalamus constantly monitors our salt concentration, as does our adrenal cortex, which is in our adrenal glands right above our kidneys. When osmolarity increases (sodium concentration goes up) these cells detect this in the hypothalamus and adrenal cortex. Two things happen at this point. Since osmolarity is increasing the body wants to rid itself of the excess sodium and conserve some water to keep the concentration down in the desired range. The hypothalamus will release ADH or anti-diuretic hormone (also known as vasopressin). ADH acts on the kidneys to conserve more water. This decreases concentration. The adrenal cortex will also inhibit production of aldosterone, which is a steroid hormone that increases sodium retention and raises blood volume levels. When blood volume increases, blood pressure also increases.
So when you get too high in sodium your body increases fluid retention and lets go of the sodium. When things go back to normal. The process slows down to allow for homeostasis. But what about when your sodium gets too low you ask? Well kind of the opposite. This can be due to very poor intake of sodium (unlikely in the United States) or because of increased intravascular volume which lowers osmolarity. It makes sense if you have a cup of water with a teaspoon of salt that if you double the volume of water the concentration of salt goes down. Now we have to activate the renin-angiotensin system. Renin is secreted into the blood which ultimately (through a few steps; angiontensinogen to angiotensin to angiotensin II) secretes aldosterone. Sodium is reabsorbed in favor of potassium. You might also begin to crave some salty food. Makes sense right, if not enough salt, the body yells at you and says,”Hey! I’m low, eat some chips or something”. This will lead to increase blood pressure as well. Angiotensin II is a vasoconstrictor so it’s not surprise that this system is the target of many, many drugs including lisinopril, enalapril, fosinopril, quinapril, make-billions-of-dollars-april, as well as many others.
So in a nutshell, when your body has too much sodium, your body gets rid of it. When it has too little sodium, it conserves it and/or yells at you to go eat something salty. I prefer my salt in the form or a nicely seasoned steak or a good paella. I try to steer clear of things like chips and dips. Most of them have crappy oils and host of other garbage ingredients that will likely not do any good for the body.
So what’s the beef….mmmm beef….with people telling us to reduce the amount of sodium in our diet? Well it turns out that a study was done called “A Clinical Trial of the Effects of Dietary Patterns on Blood Pressure” 1. AKA “DASH”. The researchers split the study subjects into 3 groups; 1 control group whose “nutrient composition of the control diet was typical of the diets of a substantial number of Americans” (1), 1 group with veggies and fruits, and a third that they called the combination diet which had less saturated fat and more calcium than the other two.
The study had a run in period of 3 weeks where all participants had the control diet. After that they were separated into their different groups and continued the study on their respective diets. The researchers had a cafeteria where food was prepared and could be consumed for lunch or dinner. All other meals were packaged and could be consumed at home. Participants could have no more than 3 caffeinated beverage/day and no more than 2 alcoholic drinks/day. On the first day, the participants were given their diet for the 30 day time frame.
Now call me crazy, but if I was given a normal American diet for 3 weeks and then fed a significant amount of fruits and veggies after 1 day, I think I might figure out that I’m on some sort of healthier diet. Mama always told me to eat my veggies, and now they’re making me. It’s possible that the people in the 2 study groups figured this out really quick and became more health conscientious. It’s also possible that people didn’t report accurately about their food intake to the researchers, even though they were paid ….I mean reimbursed and incentivized to follow the study. I’m sorry but if I tell people that if they report to me that they followed the protocol without me monitoring that they will get paid, how many people do you think will tell me the truth? Yeah.
So anyway, onto the diets.
“The potassium, magnesium, and calcium levels were close to the 25th percentile of U.S. consumption, and the macronutrient profile and fiber content corresponded to average consumption”. So from the get go, these poor saps were receiving poor nutrition, or the standard American diet (this will be refered to as SAD from now on). You can see this in the provided table from the study.
Fruits were higher in the study groups over the control group. Of course fruits will have certain qualities such as proper minerals and antioxidants that are conducive to a healthy body. Vegetable intake was more than double in the combination group than the control group. Veggies are known to be an excellent source of potassium and you’ll notice that the combo group had around 2.5 times the potassium as the control. They also had more potassium per day than sodium, where the control group had more sodium than potassium. More on that later. Veggies are also a source of antioxidants, cancer fighting agents etc, etc,etc. Another big difference was the amount of magnesium that was received. The study groups had over 400mg/day while the control had less than 200. Magnesium is known to be crucial for proper functioning of enzymes and arterial wall function. Could a large magnesium difference been enough to tip the scales one way?…maybe.
Sodium levels were kept very similar in the groups. The article did mention that participants were given two salt packets containing 200mg of sodium each for discretionary use. As far as weight is concerned, “Their weight was measured each weekday and was kept stable by changing calorie levels and by adding 100-kcal cookies or muffins with nutrient contents that corresponded to those of the assigned diets” I’m not sure I feel like this was a good thing. I know they were studying the effects of blood pressure by diets but at those caloric intakes some people could have lost weight and theoretically could have lowered blood pressure, but we won’t know. Both groups average weight and BMI were high. I know they are trying to control for variables, but introducing extra to maintain weight seems like an added variable to me.
You’ll notice quickly too that the control group had about 4 servings of snacks or sweets, whatever those entail. The ever glaring detail that looms over this study though is what I already mentioned, that the participants had essentially total control over what they wanted to eat while not at the kitchen of the researchers.
Now all those things aside does it surprise us that blood pressure was decreased? Not really. I’d be willing to bet that anyone on a SAD diet who switched to a diet rich in veggies, lean proteins and few sweets would probably lower blood pressure.
You might be asking yourself right now, “Hey buddy, what’s this got to do with sodium!?!? The intakes were the same.” And that’s my first point. They didn’t reduce sodium intake, they increased veggies and fruits that have health benefits and cut out the garbage with has anti-health benefits. What’s that you say, they still recommend low salt, below what was done in this study? Well lets take a look at another study.
This was a DASH follow up that was very similar. They had control diet and DASH diet (previously combination diet in the last study) at differing sodium intake levels. It was a crossover design so participants were getting varying levels of sodium during four 30 day periods. The sodium intakes were 150mmol/day, 100mmol/day, and 50mmol/day (3450mg, 2300mg, and 1650mg sodium respectively) .(2) Lets look at what happened.
So systolic pressure differed from the high sodium to low sodium by 3mmHg and diastolic by 1.6mmHg. That’s not really a whole lot. In fact that is small. Not only that but that is on a low amount of sodium. So low in fact have fun following that diet. It’s possible the results between the DASH groups was from mild hypovolemia, or lack of fluid in the blood, but we don’t know that.
On an anecdotal note, I remember a story one of my professors told us about following the DASH diet. She felt that she didn’t want to recommend following it without first trying it herself. She said she quickly became weak and turned pale. She had a hard time concentrating and after a week or two decided to go back on her regular diet. It didn’t inspire a lot of confidence for me in the diet and thinking about it now makes me think why the heck she’d recommend the low salt to anyone.
This study in particular is touted as one major reason why we need to drop sodium intake. Eating lots of fresh vegetables and getting rid of the garbage in your diet has seemingly escaped mainstream. I know docs and others recommend eating good veggies and what not, but this whole salt nonsense is the one that gets the most press. I guess it goes to show that things that get press often when it comes to health policy is probably just wrong or not complete.
Remember when we were discussing the biological mechanisms for the kidney to retain or get rid of sodium? Well when you have consistently low sodium intake your body has to conserve some of that because it’s needs to maintain homeostasis. So what happens? RENIN! Renin is secreted and starts the cascade to angiotensin II which then sends the message to secrete aldosterone. As you remember from above, aldosterone is a steroid hormone that retains sodium and angiotensin II increases blood pressure. Here’s the problem, if you have chronically low levels of sodium intake, this system could be activated regularly. Aldosterone also increases magnesium excretion (3) which can have an effect on blood pressure. Blood pressure is good and all but lets look at some more endpoints because a risk factor doesn’t always show us the whole picture.
In a prospective population trial, researchers looked at sodium excretion levels, which indicate sodium intake, and cardiovascular outcomes. The participants were divided into 3 groups by the amount of sodium that was excreted in the urine. The more sodium excreted, the more intake. The group with the highest amount of sodium excreted also had the least amount of deaths. Or as the article puts it, “Cardiovascular deaths decreased across increasing tertiles of 24-hour urinary sodium: from 50 in the low (death rate, 4.1%; 95% CI, 3.5%-4.7%), 24 in the medium, (death rate, 1.9%; 95% CI, 1.5%-2.3%); and 10 in the high tertile (death rate, 0.8%, 95% CI, 0.5%-1.1%; P < .001). The mean 24-hour urinary sodium excretion for each tertile was defined as 106 mmol for the low, 165 mmol for the medium; and 250 mmol for the high tertile.“(4). That’s a difference of 3.3% between the low intake and high intake. Not bad.
In another study looking at 146 patients admitted for acute decompensated heart failure, researchers looked at the difference between normal fluid and sodium intake (in the study termed at least 2.5L fluid and 3-5 gm sodium intake per day) vs a restricted fluid and sodium intake (800ml fluid and 800mg sodium). They compared weight loss, perceived thirst and clinical stabilization during a 7 day period. After 7 days there were no significant differences between the groups with the exception of thirst perception. Those who had higher amounts of sodium reported feeling less thirsty than those with low sodium. (5) Why is that important? A patient with heart failure has to be careful about too much fluid in the body because of a decreased ability to get rid of it and an increased load on a weak heart. Increased thirst could potentially lead to increased fluid intake without additional sodium, causing activation of that renin-angiotensin system we talked about earlier.
Another study looking at heart failure compared 2 groups of heart failure patients on a diet with 120mmol sodium (about 2.76gm) per day and 80mmol sodium (about 1.8gm) per day and both groups with high doses of diuretics. Both groups were allowed 1L fluid per day and were followed for 180 days with regular follow ups in the interim. The higher sodium group had a readmission rate of 7.63% while the low sodium group was at 26.32%, a significant difference. (6) The combined endpoint of mortality and hospital readmission rates were 12.71% and 39.47% in the high and low groups respectively. There was an absolute risk reduction of mortality of 8.07%, but it wasn’t significant. Still pretty impressive. The high sodium group also enjoyed a reduction of serum creatinine, which indicates improved kidney function and lower BNP than that of the low sodium group.
A meta analysis done looking at blood pressure reductions determined that it may be beneficial in the elderly crowd who already have hypertension to lower sodium, but there was little to no difference in younger normotensive patients. The reduction in the elderly for systolic pressure was 3.7mmHG and 0.9mmHg diastolic for every 100mmol decrease in sodium excretion.(7) That’s 2.3 grams of sodium being excreted! Not exactly a huge decrease of pressure and a potential for decrease quality of life.
A Cochrane review looked at hormone levels such as aldosterone, renin, epinephrine, norepinephrine, as well as cholesterol, triglycerides and of course blood pressure. The results showed that blood pressure did go down in hypertensives about the same as the above mentioned meta analysis, but all the other things I just listed increased. (8)
I don’t know about you, but I will take the 3 points of increased blood pressure over increased epinephrine and norepinephrine and aldosterone and renin any day. I think because blood pressure is so cheap and easy to measure we tend to look at that too much rather than what else is going on chemically in the body. And those chemicals are important to keep in mind while treating someone as a whole.
So when are we going to talk about potassium? I’ve been blathering on about actual endpoints and hormones. So lets look a bit at potassium.
A group did a comprehensive look of studies done regarding potassium and blood pressure. I’m not going to hit every single point because it is a rather extensive article, but here are a few things to consider when talking about sodium and potassium.
Most countries in the world have a sodium intake that is at around 100mmol or higher per day. For those that aren’t familiar with millimoles (mmol), 100mmol sodium is about 2.3 gm. I will no longer be converting. The observation with this is that many people with those levels of sodium still don’t develop hypertension, so something must be going on. (9) The article then goes on to explain how isolated populations have extremely low levels of hypertension. When the diet is analyzed, higher levels of potassium are being consumed by the isolated populations than industrialized nations. Potassium is plentiful in vegetables and fruits, something usually very lacking in a western diet. The potassium to sodium ration is 3-4:1 in the isolated populations.
This difference was seen in the above mentioned DASH study. You’ll notice that potassium was much higher in the study group than the control group by about 2.5 times. It is very likely that getting rid of garbage from your diet and adding foods high in potassium (which will likely also be high in other nutrients) will lower blood pressure as well as make you feel better.
The INTERSALT group found that a decrease of potassium excretion by 50mmol/day led to an increase of blood pressure of 3.4/1.9 SBP/DBP. (10) That means when you excrete less potassium it’s because you are eating less.
As with many of the nutrients in our diet, these two electrolytes appear to have a need to be balanced if the body is to function properly. It is probably a good idea to get much more potassium than sodium.
The last thing I want to leave you with is a review that was recently release by the National Academy of Sciences. They looked at a lot of studies and concluded that “when considered collectively, it indicates a positive relationship between higher levels of sodium intake and risk of CVD. This evidence is consistent with existing evidence on blood pressure as a surrogate indicator of CVD risk“. (11) I believe this is due to the junk we eat that is higher in sodium and the lack of potassium in the diet. A can of soup can have as much as 50mmol of sodium and as much as 1mmol of potassium. Cured and processed meats are no better. Potassium is a crucial element for human function.
The last quote comes again from the last study cited. “The committee determined that evidence from studies on direct health outcomes
is inconsistent and insufficient to conclude that lowering sodium intakes below 2,300 mg per day either increases or decreases risk of CVD outcomes (including stroke and CVD mortality) or all cause mortality in the general U.S. population”. (11) They also mentioned that there is evidence to keep sodium intake higher in heart failure patients. They generally recommend a level of 2300mg/day, which is 800mg more than the US recommendations.
I don’t think anyone should take this info as a pass to eat all the sodium you want. But I do think that you probably don’t need to count every mg either if you have a proper diet in order. I do encourage everyone to eat more potassium rich foods. With that said, don’t go out and start downing every banana you can get your hands on. Try green leafy veggies. They don’t have all the carbs bananas do (although I don’t mind carbs either, just don’t over do it).
All in all remember, be moderate.
Disclaimer: All info on this website is for education purposes only. Any dietary or lifestyle changes that readers want to make should be done with the guidance of a competent medical practitioner. The author assumes no responsibility nor liability for the use or dissemination of this information. Anyone who chooses to apply this information for their own personal use does so at their own risk.
1. L.J. Apell et. al. A Clinical Trial of the Effects of Dietary Patterns on Blood Pressure. N Engl J Med 1997; 336:1117-1124
2.Sacks, Frank M., et al. “Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet.” New England Journal of Medicine 344.1 (2001): 3-10.
3.HORTON, RICHARD, and EDWARD G. BIGLIERI. “Effect of aldosterone on the metabolism of magnesium.” Journal of Clinical Endocrinology & Metabolism22.12 (1962): 1187-1192.
4.Stolarz-Skrzypek K, Kuznetsova T, Thijs L, et al. Fatal and Nonfatal Outcomes, Incidence of Hypertension, and Blood Pressure Changes in Relation to Urinary Sodium Excretion. JAMA. 2011;305(17):1777-1785
5.Aliti, Graziella Badin, et al. “Aggressive Fluid and Sodium Restriction in Acute Decompensated Heart FailureA Randomized Clinical TrialFluid and Sodium Restriction in Heart Failure.” JAMA internal medicine (2013): 1-7.
6.Paterna, Salvatore, et al. “Normal-sodium diet compared with low-sodium diet in compensated congestive heart failure: is sodium an old enemy or a new friend?.” Clinical science 114 (2008): 221-230.
7.Midgley, Julian Paul, et al. “Effect of reduced dietary sodium on blood pressure.” Jama 275.11 (1996): 1590.
8.Graudal, Niels A., Thorbjørn Hubeck-Graudal, and Gesche Jürgens. “Effects of low-sodium diet vs. high-sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride (Cochrane Review).” American journal of hypertension 25.1 (2011): 1-15.
9.Adrogué, Horacio J., and Nicolaos E. Madias. “Sodium and potassium in the pathogenesis of hypertension.” New England Journal of Medicine 356.19 (2007): 1966-1978.
10.Intersalt Cooperative Research Group. Intersalt: an international study of electrolyte excretion and blood pressure: results for 24-hour urinary sodium and potassium excretion. BMJ 1988;297:319-28