This month's issue of Physiological and Biochemical Zoology (you all do read that, dont' you?) carries an important story of enduring signficance about how curtailed dietary intake compromises the immune systems of deer mice. Researchers Lynn Martin et al of The Ohio State University report that cutting back just 30% of dietary intake "reduces secondary antibody responses in deer mice (Peromyscus maniculatus), functionally representing a cost of immune memory." Ohio State's been doing some good work in nutrition recently.
The results are another recurring reminder of this lesson long-taught and repeatedly-reminded: there are very real physiological costs in terms of unintended consequences in reducing "normal" dietary intakes. It's been more than 20 years, for example, since Dr. Mark Cook of the University of Wisconsin published results that curtailing salt intake in chickens impaired their immune system function . That's before most of the world woke up to the AIDS catastrophe.
Today's news services ran an interesting story regarding the recommended dietary intakes for water of 9 - 13 cups as highlighted in the Institute of Medicine's Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2004) . CBS , NBC , ABC , the BBC, the Guardian , the Telegraph and Daily Mail , among others have all featured articles saying that there is not a single drop of evidence behind the myth of drinking eight glasses or more of water a day.
It turns out that the dietary recommendations from noted medical authorities as well as self-appointed health gurus to drink two or more liters of water per day are totally unsupported by any scientific evidence. Doctors Dan Negoianu and Stanley Goldfarb from the University of Pennsylvania in Philadelphia reviewed all the published clinical studies on the subject and concluded that no data exists for average healthy individuals regarding the amount of water they should consume on a daily basis.
Indeed, it is unclear where this recommendation came from," the University spokesman added.
Their research also debunked the myth that drinking water makes the skin more supple and made it easier to lose weight. "There is simply a lack of evidence in general," they reported in the Journal of the American Society of Nephrology .
Reuters reports that this was not the first time such a conclusion was made since Dr. Heinz Valtin of Dartmouth Medical School found the recommendations to drink that amount of water to be totally lacking in scientific merit.
Because we all have specific individual needs for water, Goldfarb recommended, "If you're thirsty, drink. If you're not thirsty, you needn't drink."
This most recent article highlights the specificity of an individual's metabolic need, a situation paralleled by salt intake. The human body has an ability to excrete 250 times the maximum recommended intake of salt - an amount of salt that is virtually impossible for anyone to consume. In other words, our salt consumption is not limited by our ability to excrete it, but rather by our innate senses - sensory perception and biological feedback mechanisms. Both of these mechanisms are specific for every individual, just as water is.
For this reason, it is the very same folly to apply a "one size fits all" set of policy recommendations to salt consumption as it is for water consumption. Salt consumption is self-limiting and regulated by nature's biology, not by shortsighted dietary recommendations.
A Swedish-led group of European researchers set off to document the relationship between dietary electrolytes (magnesium calcium, potassium and sodium) and stroke risk. The ended up documenting the lack of an association of sodium and risk of stroke, adding to the lengthening list of "health outcomes" studies which are remarkably consistent in their conclusion: reducing dietary salt won't improve health.
Published in the March 10 issue of the Archives of Internal Medicine , the researchers studied 26,556 older Swedes; all were smokers. Over the 13.6 years of the study, the group recorded 579 stroke events. The population had extemely high salt intakes; the average sodium intakes for the five quintiles of sodium ranged from 3,909 mg/day to 5,848 mg/day (the U.S., by comparison averages about 3,500 mg/day -- lower than the lowest 20% of the Swedes in the study).
The findings: stroke incidence was nearly identical in all five quintiles and not only was there no trend in the pattern, but of the 30 separate analyses performed, not a single subgroup had a significant relationship between sodium and stroke incidence. Add this study to the list.
A long plane ride today afforded the opportunity to read an Anthony Daniels review of Ibn Warraq's new book , Defending the West: A Critique of Edward Said's Orientalism. Daniels uses what Benjamin Franklin in the play 1776 said of Thomas Jefferson's writing skills: "a peculiar felicity of expression."
That expression, offered in the context of refuting Said's famous book, was offered as printed:
Some might say that Ibn Warraq has picked an easy target: Said's work would not have been worth refuting had it not been so phenomenally successful in creating what Auden called, with regard to Freud, "a whole climate of opinion."
Whatever you think about the Said/IWarraq contention, our attention was captured by the strong parallel of Said's conventional wisdom versus Warraq's critique to the Salt Institute's recurrent attempts to engage federal public health nutrition leaders in a discussion of the weakness of the scientific data offered in support of the contention that lowering dietary salt will improve health.
To paraphrase: if the federal anti-salt advocacy campaign hadn't been "so phenomenally successful" in creating a "climate of opinion" condemning salt, it would, in Warraq's appropriate words "would not have been worth refuting." Of the fifteen studies of health outcomes of salt-reduced diets , nearly every one has found no benefit and many have found additional risk.
We need a controlled trial to sort out the issues raised in these studies; all of them are merely observational. But the lack of any likelihood that a controlled trial would validate the notion of a health risk of current levels of dietary salt is trumped by the obvious fact that this unsubstantiated policy is already in place. So, even though the "hypothesis generating" studies would suggest the negative hypothesis, that lowering dietary salt would NOT improve health outcomes, the existence of the current policy based on the contrary assumption, though ostensibly "not worth refuting" is actually well worth examining.
Let's let the science guide our policy, not the momentum of obsolete assumptions. Secretary Leavitt, fund a health outcomes study of salt-reduced diets. Please.
NPR (National Public Radio) hit the nail on the head with this just-out story: "Doctors' 'Treat the Numbers' Approach Challenged ." As correspondent Richard Knox explains:
It can take scientists a decade or more to determine whether a drug actually works. In the meantime, doctors rely on other measures, like testing blood pressure and cholesterol levels, to determine whether a drug is having positive effects. But recent studies challenge the practice of prescribing medicine based on certain test results.
Doctors call it "treating the numbers" - trying to get a patient's test results to a certain target, which they assume will treat - or prevent - disease.
Knox quotes Dr. Steve Atlas of Mass General hospital: "It's a big deal because it reminds us of something that we often forget: the number isn't the outcome. And this raises concerns that just lowering the number doesn't get you where you want to be," (emphasis added)
This is, of course, exactly what our public health nutrition policy on salt is doing: treating the number. We need to look at outcomes (see numerous earlier posts to this blog).
Knox also quotes Dr. Ned Calonge on cholesterol-lowering drugs based on the recent diabetes trial disaster , saying:
"Now, what's open is - is lower better? And I think a lot of people believed it would be, and there are many of us that were saying, 'You're going to need to show me,' " he says.
Lately, studies have also challenged other cherished assumptions - like lowering blood sugar. For a long time, doctors have believed that getting diabetic patients' blood sugar as close to normal as possible would prevent heart attacks. A drug called Avandia lowers blood sugar very well.
It was approved in 1999 and was heralded as "one of the newer and greater drugs for the treatment of diabetes," says Dr. Cliff Rosen. Rosen is the chairman of a Food and Drug Administration advisory panel that concluded unanimously last year that patients taking Avandia actually had more heart attacks and strokes.
Rosen says the Avandia story is a caution against treating millions of patients on unproven assumptions.
It's the same story for salt -- but, so far, a largely-untold story. Still, just as public health policy cannot change human physiology, neither can news coverage. But it can slow down our quest for the truth and our ability to base policy on evidence rather than opinion. Please, someone tell HHS! Outcomes matter.
USA Today published a story today echoing the CASH/WASH mantra that children eat too much salt. Our reply:
Kim Painter's article ignores two important points of science. First, salt reduction in children and adults may be related to blood pressure, but because salt reduction triggers other reactions , it has not been shown to lower the rate of heart attacks or cardiovascular mortality. That cherished assumption has been demolished by evidence over the past 13 years. Second, humans and other animal species eat salt in predictable amounts when they can get it; our salt intake is unchanged over the past century. Research published in the February issue of Experimental Physiology explains that the brain's neural system system provides multiple, redundant systems to make sure our salt appetite ensures we get enough salt. Salt is an essential nutrient. We die unless we eat salt.
Let's let the science guide this policy. The U.S. Preventive Services Task Force , the government's in-house advocate for evidence-based policy, has found evidence insufficient to advise the general population to reduce dietary salt. Ditto the Cochrane Collaboration , the global inventor of "evidence-based" decision-making in medical science.
For more information, check the Salt Institute website, http://www.saltinstitute.org/28.html. .
Dick Hanneman President, Salt Institute
Britain's Food Standards Agency asks: "Are we 'bad science' junkies?" Well, yes you are. The regulators, of course, aimed their barbed inquiry at what they perceive is an insufficiently alert public that can't separate fact from fiction with regard to the scientific basis for dietary recommendations. In their mind, salt is the exception; they aver: "There was good awareness of the risks associated with eating too much salt."
Well, no there isn't "good (public) awareness of the risks associated with eating too much salt." The public has followed FSA down the "bad science" pathway and been convinced that science supports general salt reduction. Wrong. Any fair-minded reading of the literature addressing the question "will reducing dietary salt improve health" shows scant evidence for a health benefit and far more data suggesting actual increased risks.
FSA conducted the survey for the launch of the first meeting of the independent General Advisory Committee on Science (GACS) which will open its proceedings with a panel debate to look at the question 'Should we trust what scientists say about food?'.
Our suggestion: let's query the data, not the scientists. Good science is empirical, not expert opinion. Evidence-based medicine considers expert opinion only a Class D level of evidence.
Before 1991, very little cholera was reported in Peru. Then, under unusual circumstances, it infected Peru's coastal waters and the fish which are so important to the local diet. The organism responsible for cholera, Vibrio cholerae occurs naturally in the plankton of fresh, brackish, and salt water, attached primarily to copepods in the zooplankton. The coastal waters were unusually warm and untreated sewage supported unusually large zooplankton blooms.
In order to quell the bad publicity regarding the quality of his country's coastal waters, then President Fujimori wished to demonstrate to his citizens that the press reports were exaggerated. He boldly posed for public television cameras eating some locally-prepared ceviche. Within 12 hours, he came down with cholera confirming that pathogens are a biological, rather than a political phenomenon. That cholera outbreak eventually killed 3,500 people.
Fortunately, doctors quickly turned to effective and inexpensive oral rehydration therapy with clean water and salt. If not, the death toll would have been much greater.
Cholera is characterized by prolonged episodes of diarrhea and it is critical to ensure that lost fluids and salts are fully replaced. Common table salt (sodium chloride) is the key electrolyte that has to be replenished along with water.
Now some officials worry that climate change could bring the scourge back to Peru and are making doubly certain to make the population aware of the need to keep themselves fully hydrated and electrolyte-balanced, proving once again that salt is an essential element of life and good health.
To give credit where it's due, Junk Food Science today touched another nerve on a topic seemingly far afield from concerns of the salt industry, but on closer examination, there are alarming parallels.
CBS Evening News reported the story yesterday that an idea generated by a handicapped 16-year old in a high school "There Ought to be a Law" writing contest has been introduced as a bill in the California state legislature. As JFS's Sandy Szwarc explains:
The bill will require all poor women receiving welfare benefits to be tested for narcotics. Those who test positive will be required to undergo treatment or lose their public assistance, including healthcare. The rationale behind the bill is to dispense state healthcare dollars prudently and to protect children from health problems due to women who do drugs while pregnant.
Her concern (and ours) is the "slippery slope" of the argument. In this case, I'd posit, very few would defend the behavior of narcotics use. Certainly every taxpayer also wants government health care costs curtailed. Where do you stop? Which unhealthy actions should be used to deny public welfare benefits (and what benefits? food stamps or Social Security, Medicare, etc.?). Smoking, for example. Should smokers be ineligible for taxpayer-subsidized Medicare hospitalization? What about binge drinkers? Over-eaters (or those not following the Dietary Guidelines)? For some, hard evidence might actually show the behavior caused a burden on taxpayer services, but it could extend to other non-data-driven, politically-correct behaviors such as buying foods not labeled "low salt" or sprinkling salt on your food in a restaurant (surely, we'll still be able to eat as we please at home!). Far fetched? I hope so; I fear not.
It was personally deeply disappointing to read the publication today by my respected, esteemed, even revered think tank, the American Enterprise Instittute (AEI) of a superficial review of the salt and health controversy. Research assistant Sara Wexler properly concluded that FDA regulation of salt was a blind alley, but, instead, she urged "low-sodium campaigners (to) focus their efforts on consumer demand."
This was "think tank lite" at its worst. Both the facts and the analysis were flawed. In fact, the entire article was written to address the wrong problem altogether. This is a worthy subject for a serious AEI analysis, but this wasn't a serious AEI analysis in the proud tradition dating back to Murray Weidenbaum and Chris DeMuth. A sad day.
Where to begin? Let's start with a few facts.
Wexler states the Salt Instittute (and Grocery Manufacturers Association) "have called for voluntary sodium reductions instead of federal regulation." I'll let GMA speak for themselves. The Salt Institute feels that patients should follow their doctors' advice on dietary sodium, but we strongly oppose a general recommendation for sodium reduction. Wexler continues, accurately, to report that the Salt Institute, GMA and the International Food Information Council have concluded that the medical evidence shows "the direct impact of sodium reductin on human health is still unclear." True. That's why we oppose it. Why would we think a "voluntary" program to undertake a major, unjustified health intervention would be appropriate? We don't.
Wexler conflates "blood pressure" and "health risks" regarding dietary sodium. Experts agree salt is related to blood pressure and, indeed, as reported, research at the University of Indiana shows that in a strong majority of people', their blood pressure is unchanged on a low-salt diet while a significant minority actually increase their blood pressure and more has the "desired" fall. But experts do NOT agree that evidence shows that reducing dietary salt actually improves health. In fact, most of the health outcomes studies find no benefit at all and several have found possible risks when people cut back salt. That said, Wexler correctly reports the Salt Institute's support for improving overall dietary quality to improve risks.
Wexler points out there is "confusion" on the issue, but she states that "(t)he biggest problem for industry groups seems to be the lack of adequate demonstrative studies." That's just wrong. First of all, the problem isn't an "industry" problem, it's a "health" problem. The prospect of imposing billions of dollars of additonal cost on American food consumers is not the issue here (though legitimate), the question is whether evidence shows that the proposed major re-engineering of the American food supply has any scientific justification and whether the intended benefit will be sacrificed to unintended consequences. The "confusion" isn't with the evidence. The confusion is caused by those who persist on ignoring the evidence of a lack of a health benefit and suggesting that the "industry" should fund the research to document the government's policy. As an aside, HHS has stonewalled release of key data at every step and fought an attempt by the Salt Institute and the US Chamber of Commerce to force transparency in the process.
Wexler implies FDA's regulation awaits a determination of "(w)hether or not sodium can be linked to high blood pressure." We certainly hope not. And all Americans should hope that FDA should not consider regulations in this area until it can show that 1) reducing salt will improve health and 2) regulating the amount of sodium in individual foods will reduce overall dietary sodium intakes sufficient to achieve a health benefit. Neither has been shown. That's why the US Preventive Services Task Force has concluded there is a lack of evidence for a general salt reduction recommendation.
Wexler seems to consider salt to be just another nutrient, like fat, carbs and sugars, ignoring the fact that it is an essential nutrient necessary for life. As such, the body has redundant systems to ensure an appetite for salt, as discussed as recently as this month's Experimental Physiology and discussed in our blog by both Mort and me . What this suggests is that "consumer demand" will never be the answer.
We won't get the right answer until we start asking the right question: Will a low-sodium diet improve health? We may need to go no further. HHS should fund the controlled trial of this question that will answer this serious question.
Wexler's once-over-lightly piece is fluff. We expected more from AEI.
Less than 20 percent of U.S. adults with high blood pressure eat foods that align with government guidelines for controlling hypertension, a recent study found .
This outcome is no great surprise. The American Heart Association (AHA), the American Medical Association (AMA) and the National Heart Lung and Blood Institute (NHLBI) have all deliberately mislead the public by spinning the results of the DASH-Sodium trial to indicate that most of the blood pressure benefits were the result of salt reduction. It is hard to say if this myth-information was the work of specific individuals within these organizations or the organizations themselves. What is critical, however, is that these organizations have not lived up to their responsibilities and barely promoted the importance of the DASH- or Mediterranean-type diet in reducing cardiovascular disease. Instead, they have adopted the magic-bullet, single nutrient approach and almost exclusively promoted salt reduction as the dietary approach to improve cardiovascular health. That is why so few U.S. adults now follow the DASH diet.
It is time that the credibility of these organizations comes under far greater public scrutiny. The recent disasters of hormone replacement therapy and the disasterous strategy to aggressively drive down blood sugar in diabetes patients are clear examples of our medical establishments doing harm with ill-considered policies and information.
The following graph encapsulates the results of the DASH-Sodium trial:
It is immediately apparent that moving from a regular U.S. diet (blue line) to a DASH-type diet (red line) has a far greater impact on blood pressure than lowering salt consumption. On the regular diet, dropping from the current level of sodium consumption to the recommended daily level of 2,300mg Sodium/day dropped the systolic pressure by an average of 2.1 mm Hg (mercury). However, changing from a regular U.S. diet to the DASH diet, without any changes to sodium consumption, reduced the systolic blood pressure by 5.9 mm Hg, almost three times the drop resulting from the sodium reduction! There is no equivalency here. The move to a DASH diet far exceeds the benefits of salt reduction - there is no comparison. This clearly explains why Mediterranean people enjoy an excellent cardiovascular status despite their high salt consumption, as mentioned in a previous article . With a DASH diet, the impact of sodium on the blood pressure of hypertensives is minimal (and is of no significance to normotensive people - the majority in the population). On top of that, the DASH- or Mediterranean-type diet has myriad other health benefits aside from reducing blood pressure.
Yet, the AHA, the AMA and NHLBI always spin the data to place the majority of the benefits on salt reduction first and then the DASH diet, almost as an afterthought. In lock step, the Center for Science in the Public Interest (CSPI) repeats this in much the same manner.
What a pity that people take their advice!
No wonder we see headlines like, "Not many follow anti-hypertension diet " or "Fewer hypertensives adhering to DASH diet " or "Most With High Blood Pressure Do Not Follow Recommended Diet ". AHA, the AMA and NHLBI must all share in this predictable consequence of myth-direction.
NY Times op ed contributor Gary Taubes weighed in on the recent Vytorin flap , registering insights with equal applicability to the ongoing salt controversy. Said Taubes of lessons to be learned from the cholesterol trial:
(The authors') interpretation is based on a longstanding conceptual error embedded in the very language we use to discuss heart disease. It confuses the cholesterol carried in the bloodstream with the particles, known as lipoproteins, that shuttle that cholesterol around. There is little doubt that certain of these lipoproteins pose dangers, but whether cholesterol itself is a critical factor is a question that the Vytorin trial has most definitely raised. It's a question that needs to be acknowledged and addressed if we're going to make any more headway in preventing heart disease. ...
The truth is, we've always had reason to question the idea that cholesterol is an agent of disease. Indeed, what the Framingham researchers meant in 1977 when they described LDL cholesterol as a "marginal risk factor" is that a large proportion of people who suffer heart attacks have relatively low LDL cholesterol.
So how did we come to believe strongly that LDL cholesterol is so bad for us? It was partly due to the observation that eating saturated fat raises LDL cholesterol, and we've assumed that saturated fat is bad for us. This logic is circular, though: saturated fat is bad because it raises LDL cholesterol, and LDL cholesterol is bad because it is the thing that saturated fat raises. In clinical trials, researchers have been unable to generate compelling evidence that saturated fat in the diet causes heart disease. ...
One obvious way to test the LDL cholesterol hypothesis is to find therapies that lower it by different means and see if they, too, prevent heart attacks. This is essentially what the Vytorin trial did and why its results argue against the hypothesis. ...
Because medical authorities have always approached the cholesterol hypothesis as a public health issue, rather than as a scientific one, we're repeatedly reminded that it shouldn't be questioned. Heart attacks kill hundreds of thousands of Americans every year, statin therapy can save lives, and skepticism might be perceived as a reason to delay action. So let's just trust our assumptions, get people to change their diets and put high-risk people on statins and other cholesterol-lowering drugs.
Science, however, suggests a different approach: test the hypothesis rigorously and see if it survives. If the evidence continues to challenge the role of cholesterol, then rethink it, without preconceptions, and consider what these other pathways in cardiovascular disease are implying about cause and prevention. A different hypothesis may turn out to fit the facts better, and one day help prevent considerably more deaths.
To reiterate the lesson: rather than accept that high blood pressure is a problem that demands such urgent action that we sacrifice the discipline of conducting a health outcomes trial of the intervention, we should, as Taubes argues, "the hypothesis rigorously and see if it survives." If the evidence continues to challenge the role of (salt), then rethink it, without preconceptions, and consider what these other pathways in cardiovascular disease are implying about cause and prevention. A different hypothesis may turn out to fit the facts better, and one day help prevent considerably more deaths." Good plan.
Health outcomes matter. We were reminded yet again this week that entirely-plausible, widely-accepted, even vociferously-advocated interventions still need to be supported by rigorous scientific data. Headlines in the Washington Post screamed: "Deaths Halt Part of Diabetes Study. Scientists Fear Heart Attacks, Strokes Were Tied to Treatment. "
The headlines were similar to those when the feds halted part of the ALLHAT trial of anti-hypertension drugs because, while lowering blood pressure, they weren't reducing heart attacks or strokes. The headlines mirrored those when the government embarrased itself advocating Hormone Replacement Therapy (HRT) for post-menopausal women only to find it was killing them. After all, scientists had offered untested assurances that the interventions "can't hurt anyone."
Soon, the same headlines may be written to apply to advice to lower dietary salt.
Public health leaders are so anxious to overcome serious and perplexing health problems that they lose their discipline. They set aside standards of evidence-based medicine that demand scientific support before approving an intervention. Everyone wants heroes. Certainly the researchers want success. So do the intervention sponsors, whether a pharmaceutical company or an activist lobby group like, in this case, the American Diabetes Association. So do the media; overcoming a dread health threat is important news. All of us, frankly, want these interventions to work. But we cannot ignore the discipline of the scientific process in our enthusiasm and zeal. And we need to temper our noisy presumptions, the arrogance that we know all the answers and now have only to force implementation of strategies never fully tested, with a profound humility. Pride goeth before the fall.
So this week's news was that adverse findings "stunned and disappointed experts." Rob Stein reported in the Post story:
Aggressively driving blood sugar levels as close to normal as possible in high-risk diabetes patients appears to increase the risk of dying from a heart attack or stroke ...
The findings are the second major blow to widespread assumptions about how to protect against heart disease -- the nation's leading killer. Another recent major study found that driving blood cholesterol levels as low as possible did not necessarily slow the progression of heart disease.
Many earlier studies had shown that tightly controlling blood sugar significantly reduced the risk of many complications. The new study -- known as the Action to Control Cardiovascular Risk in Diabetes, or Accord, trial -- was designed to convincingly test whether various aggressive treatment strategies reduced the risk of heart disease -- the main cause of death among diabetics.
The study involves 10,251 patients ages 40 to 82 at 77 sites in the United States and Canada at high risk for heart disease for any reason, such as high blood pressure, high cholesterol or obesity. About half were placed on a regimen combining diet and exercise with commonly used drugs designed to lower their blood sugar levels to those of the average person with diabetes, while the other half were put on a more intensive regimen designed to drive levels closer to those of someone without diabetes. The patients were further divided into those who also received blood-pressure-lowering medication or drugs to improve their cholesterol levels.
Over about four years, about half of the patients getting intensive treatment achieved blood sugar levels close to normal, and about half the patients in the standard treatment group achieved levels close to the average diabetic.
But a special 10 member panel that was monitoring the study alerted the organizers that 257 patients r eceiving intensive treatment had died, compared with 203 receiving standard treatment, a difference of 54 deaths -- or 3 per 1,000 participants per year, officials said. About half the excess deaths were from heart disease.
Stein interviewed Cleveland Clinic cardiologist Steven Nissen, who seemed chastened, admitting: "This suggests that there are things drugs do that we don't understand."
The potential for unanticipated (and adverse) consequences is why we give lip service to supporting evidence-based medicine. Then along comes a plausible answer to an important problem and we must show discpline and humility to say: sounds great, let's find some money and test it out to see if it's true.
In August 2006, international experts joined the Salt Institute in urging the U.S. Department of Health and Human Services to find funding for a controlled trial of the question: will lowering dietary sodium improve health, specifically cardiovascular risk and mortality? We were told, in effect, that this was our problem and we should fund the study despite the fact that HHS's own U.S. Preventive Services Task Force has determined there is no evidence supporting population advice to reduce dietary salt.
It's time for some discipline and humility, HHS. And some funding.
Medical experts dispute the importance of curtailing dietary salt. Experts focused on blood pressure favor cutting salt. Experts focused on reducing heart attacks and protecting cardiovascular health disagree and favor an approach of improving overall dietary quality. A new study suggests the 30-year debate may have been irrelevant; human physiology has multiple systems that ensure proper intakes of salt and water to protect health. As Mort summarized recently on SaltSensibility , the body has redundant systems and is self-regulating. No matter what the experts may advise, our unique consumption level for salt is "hard-wired" into our systems to protect our health against do-gooder meddling:
This latest publication shows that this multi-factorial system is so robust and includes so many failsafe mechanisms that it continues to fully function even after large sections of its system are shut down. Employing a complex cascade of physiological functions from powerful hormones, such as aldosterone, to pressure sensitive receptors in the brain, this water thirst and salt appetite mechanism moderates our behavior so that we are driven to quickly replenish the volume and ionic balance of our blood, so that it is pressurized sufficiently for our heart to circulate it through our bodies. When fluids and electrolytes are lost, such as with sweating, physical exertion, diarrhea or other circumstances, we immediately get a water thirst signal. So we drink water to make up the loss. After a delay, our salt appetite kicks in to ensure that the ion levels are replaced. If we don't respond on time to the salt appetite, we die.
The article, "Central regulation of sodium appetite " appears in the February issue of Experimental Physiology.
In a strikingly clear and comprehensive manner, the paper entitled "Central regulation of sodium appetite ," by Joel Geerling and Arthur Loewy of the Department of Anatomy and Neurobiology, Washington University School of Medicine in St Louis, MO, elaborates the mechanisms responsible for our appetite for salt. The physiological apparatus we have evolved over the eons to maintain a fully operational cardiovascular system is largely dependant upon maintaining both a balance and sufficient quantities of the two nutrients most essential to life, water and salt. This fundamental system is can be found in fish, reptiles and all mammals. Life depend on it.
In order for us to survive, our circulatory system must have an adequate volume of blood that is under sufficient pressure to supply all our tissues with the nutrients they need and to remove all the toxic byproducts of metabolism. It is a finely tuned balance of water and salt that allows this to happen. Any amount of water or salt that is consumed in excess of our needs is quickly eliminated through our kidneys. However, an equally important issue is ensuring that we have ingested enough water and salt to make up for any losses we experience. This is where the incredible mechanism controlling the thirst for water and the appetite for salt comes in.
This latest publication shows that this multi-factorial system is so robust and includes so many failsafe mechanisms that it continues to fully function even after large sections of its system are shut down. Employing a complex cascade of physiological functions from powerful hormones, such as aldosterone, to pressure sensitive receptors in the brain, this water thirst and salt appetite mechanism moderates our behavior so that we are driven to quickly replenish the volume and ionic balance of our blood, so that it is pressurized sufficiently for our heart to circulate it through our bodies. When fluids and electrolytes are lost, such as with sweating, physical exertion, diarrhea or other circumstances, we immediately get a water thirst signal. So we drink water to make up the loss. After a delay, our salt appetite kicks in to ensure that the ion levels are replaced. If we don't respond on time to the salt appetite, we die - a situation which was described in an earlier article where a young woman died in a water-holding contest.
It has been repeatedly suggested that policies must be developed to reduce the amount of salt in processed foods. In fact, some countries already have or are in the process of considering policies to effect this. Will these policies be effective? What indication is there that people who are provided with a lower-salt food supply will actually reduce their intake of salt? Based upon this latest publication on salt appetite, individuals faced with foods that are mandated to be low in salt may make up for this in other ways. They may eat considerably more food in order to get more salt or they may simply pick up the salt shaker and add more voluntarily.
The recent publication by as described in a recent article legitimately brings up the question of minimum levels of salt intake. Based upon their data, we can justifiably ask whether the current recommended daily values are prudent. Should the 2,300mg daily upper limit for sodium be reconsidered? Should the Institute of Medicine recommended daily adequate intake of 1,500mg sodium be reconsidered?
Our thirst for water is a basic mechanism we have evolved in our fight for survival. So is our appetite for salt. It is time we realize that the two mechanisms are interdependent and basic to our survival. Any policies promulgated to regulate our consumption of salt must bear this in mind and be based on the most rigorous science. If not, harm will be done.