© 2001 Whole Foods magazine
Potassium-to-Sodium Ratio Affects Overall Health
Part 4: Potassium, Sodium and Dementia.
An interview with Mark McCarty
This segment concludes our four-part interview with the three authors of The Salt Solution a landmark book that outlines what is perhaps the greatest danger in the American diet - too much salt and too little potassium.
In this month's installment, co-author Mark McCarty tells us about the link between a low K Factor diet and dementia. As you may recall, Mark was a medical school "dropout" some years ago, who then devoted his career to applied nutrition. He has long been a colleague of Herb Boynton, the founder of Nutrition 21 and another of the co-authors (along with Richard D. Moore, M.D., Ph.D.) on The Salt Solution. Mark is currently president of NutriGuard Research, a supplement company he helped to found, and he also holds consulting positions with Pantox Laboratories, Nutrition 21 and Natural Alternatives. To date, he has authored over 100 publications in the refereed biomedical literature, most of which have appeared in the journal Medical Hypotheses.
Passwater: In the July issue, we left off with a discussion of Dr. Staffan Lindeberg and some fascinating discoveries he made about the indigenous people of the tiny island of Kitava off the coast of Papua New Guinea. Specifically, you said that he claimed to have found no evidence of senile dementia among this population. May we get back to Dr. Lindeberg and his discoveries?
McCarty: Sure. Naturally, Dr. Lindeberg is fully aware of the evidence that essential hypertension, as well as the age-related rise of blood pressure, are virtually absent in low-salt societies. But he thought it would be interesting to see whether he could carry this inquiry further and determine whether avoiding salt and hypertension would have a correspondingly favorable impact on risk for stroke. Actually, some recent epidemiology suggests that salt intakes have a more impressive impact on stroke risk than on hypertension risk or on blood pressure. In other words, salt increases your risk for stroke in ways that have nothing to do with blood pressure-implying that a salty diet may be dangerous for one's cerebrovascular health even when blood pressure is considered normal. And everyone should be aware that, whereas high blood pressure can greatly increase the risk of a stroke, the majority of elderly people who have strokes in fact have "normal" blood pressure!
Dr. Lindeberg became aware of an island off the coast of Papua New Guinea called Kitava where the residents have never added refined salt to their food. In fact, there are very few aspects of Western civilization that have caught on there with the exception of tobacco smoking. Most of the adults are tobacco addicts, and they import cigarettes from the West. But aside from that, they incorporate Western foods only to a trivial extent and, in particular, they have never imported salt or added refined salt to foods. They do cook in seawater to some extent, so that their diet is by no means salt-free, but Dr. Lindeberg was able to estimate that they probably don't get much more than 1,000 mg of sodium a day, which means their salt intake is probably about a quarter of what it averages among people in the United States.
Dr. Lindeberg realized that Kitava offered us a priceless-and probably fleeting-opportunity to examine the impact of unsalted diets on risk for stroke and other vascular disorders. So he organized a Swedish scientific expedition to Kitava and spent a number of months getting to know the Kitavan people and conducting extensive clinical examinations in an effort to determine what proportion of elderly Kitavans had suffered a stroke or had heart disease. 'There are about 2,500 people on the island, a fair percentage of whom are over 70, so he had plenty of people to examine. Lindeberg had an excellent translator with him, and the Kitavans were very helpful and articulate. But they initially were wary about the drawing of blood. One of the big heroes of the whole project was a very old Kitavan man who, after having his blood drawn, walked around the whole rim of the island just to demonstrate to his colleagues that blood drawing doesn't harm you!
Dr. Lindeberg conducted physical examinations on a large number of elderly Kitavans, with the intent of eliciting any evidence that they may previously have suffered a stroke or heart attack, or had coronary heart disease. But he also supplemented this information by asking the whole tribe whether they were aware of any person in the tribe who had experienced symptoms suggestive of a heart attack or stroke. The bottom line is that he was unable to unearth any evidence that anyone on the island had ever suffered a stroke or heart attack! Obviously, he wasn't able to completely rule out that possibility, but it was quite clear that if these disorders existed at all on Kitava, they were extremely rare. The closest he came to a suggestive episode was a story he heard independently from several different people about a man in his 70's who was walking on the beach and fell over dead for no apparent reason.
This incident occurred in the late 19th century! This should give you an idea of how well the Kitavans hang on to their history! In any case, Lindeberg was completely successful in confirming his suspicion that lifelong consumption of a low-salt diet confers almost total immunity from stroke. Back during the early 20th century, there were reports that stroke was extremely rare among black Africans whose diets were low in salt and who seemed immune to high blood pressure-but Lindeberg's study provides even more convincing documentation of this point.
Passwater: Please tell us more about their diet.
McCarty: It is quite interesting. They get the majority of their calories from tropical tubers, namely yams and sweet potatoes, which are of low caloric density and extremely high in potassium per calorie. They have no cereal products in their diet, except for a bit of corn in the autumn. Grain products, even whole grain products, usually are not very high in potassium. Fruit, coconuts, greens, wild beans, and a small amount of fish-about 5% of calories-round out their diet, which thus is "pesco-vegetarian." I have estimated, based on the food consumption data that Dr. Lindeberg published, that these people are getting around 8,000 mg of potassium a day, which is about triple what we get in the United States. All in all, I think their potassium-to-sodium ratio is about 12 times higher than ours, so that is a very major shift-virtually replicating a Paleolithic level of potassium and salt intake.
One interesting aspect of the Kitavans' diet is that it contains a fair amount of saturated fat. In fact, about 18% of their calories come from saturated fat because they eat a lot of coconuts. However, their diet also provides a meaningful amount of protective omega-3 fats owing to their fish intake, whereas their omega-6 intake is quite low, inasmuch as their diet is quite low in grain products. So the omega-3/omega-6 balance favors omega-3. Another factor likely to be relevant to their excellent vascular health is that they are greyhound-lean throughout life. Their body mass index (BMI) is around 20 to 21, and their insulin levels actually decrease as a function of age, which is, of course, the inverse of what we see in the West. This implies excellent insulin-sensitivity. In fact, not a hint of diabetes is seen among these people.
Passwater: The BMI is an individual's body weight in kilograms divided by his/her height in meters squared. A BMI of 25 is considered overweight and a BMI of 30 is considered obese.
McCarty: I think the main things the Kitavans have going for them from the standpoint of vascular health are lifelong leanness, insulin-sensitivity, a meaningful amount of omega-3 in their diet, and a whole-food, near-vegan diet that has a remarkably high potassium-to-sodium ratio. In addition, Dr. Lindeberg found that their blood contained a low level of the clot-promotion factor called PAI-1. He noted that this particular component was only about half as high in Kitavans as in Swedes. It would seem that their excellent insulin sensitivity contributes to this, but it also is possible that the Kitavans have some genetic advantage in this regard. You have to balance these protective factors against the fact that they have a high saturated fat intake, As a result, their blood cholesterol levels are not notably low. I recall that they average about 180 in the men and 220 in the women. Also, about 80% of the adults are tobacco addicts. You can bet that the coronary care units in the U.S. are filled with people who smoke and have cholesterol levels in the 180-220 range- yet the Kitavans display no sign of heart disease at all!
Passwater: That is so intriguing. And, of course, Lindeberg also had been unable to find any evidence of stroke among these people.
McCarty: Quite right! This is particularly interesting when compared to the experience in many other Third World cultures, where heart attack has been rare, but stroke usually is quite common. Meanwhile, a careful reading of one of Dr. Lindeberg's papers brought up a point that I found of exceptional interest. He devoted just a couple of sentences to the observation that he saw no evidence of senile dementia on Kitava, and that all the elderly seemed to be mentally well-preserved.
Passwater: Let me first clarify a point. We haven't spoken of life span. Is there a significant number of elderly Kitavans?
McCarty: Yes. Proportionally, there are many people in their 70s, 80s and even a few in their 90s.
Passwater: I just wanted to make sure that none of the readers draws the conclusion that Kitavans all die relatively young. If they did, that would, of course, cut down the chances of developing strokes or dementia
McCarty: There is a misimpression that, because the average life span in a lot of Third World countries may be relatively low compared to ours, there would be a paucity of elderly people in these societies. In fact, the average diet confers almost total immunity life span usually is skewed by infant or childhood mortality. I recall call reading that the average 40-year old Bolivian Indian with virtually no access to medical care has a longer life expectancy than a 40-year old resident of the U.S. In other words, if people in these cultures manage to make it through infancy and childhood without succumbing to infection, they have quite a decent chance to become elderly.
The chief causes of death in Kitava are infection and trauma. Also, there are a few very elderly Kitavans who have died in their sleep for no apparent reason, without symptoms suggestive of a heart attack or stroke. Perhaps their aging heart muscles just wore out and they had an arrhythmia. Aside from ovarian cancer-10 cases of which have been documented-cancer seems to be rare (although without autopsies, it is difficult to be sure). There is only one known case of a breast cancer that eroded the overlying skin. The fact that the Kitavan diet consists of low-glycemic index whole foods, and is vegan aside from a modest intake of fish that provides cancer-preventive omega-3, suggests that they should be at low risk for cancer-in part because this diet keeps them very lean and insulin-sensitive. The only fatality that occurred while Dr. Lindeberg was there was that of a 70-year-old man who fell out of a palm tree. We don't have too many 70-year-old people in the U.S. shinnying up to the tops of palm trees, but I suppose if we did, we would have a fair number of palm tree fatalities!May I make one other comment about Kitava? It is rather peculiar that these people do not have low cholesterol levels, and most of them smoke-yet there is zero evidence of coronary heart disease in Kitava! That suggests to me that if you eat an unsalted diet and stay lean and insulin-sensitive all your life, this may have a profoundly protective impact that overrides the impact of LDL cholesterol and even smoking. Perhaps salted diets are a permissive factor for heart disease. Do we know of any society eating an unsalted diet that has a significant incidence of coronary disease? I am not sure we do. Of course, the problem is that, as people adopt Westernized diets, salt consumption goes hand in hand with all of the other poor dietary habits that promote vascular disease. I'm not aware of any Third World society that adopted diets high in fatty animal products and refined grains, that didn't simultaneously become addicted to salt. So we can't tell whether avoiding salt would have protected them from the other aspects of this diet. The Kitavans are unique in that their relatively high cholesterol levels stem from the use of coconuts, not from any fatty animal products.
Passwater: How about the physical activity of these people? I know they are not couch potatoes, but, I would assume, neither are they marathon runners.
McCarty: Not at all. They probably would laugh at us for doing aerobic exercise. Obviously, there is a certain effort involved in gathering their food, but the impression that I get from Dr. Lindeberg's work is that while they are probably somewhat more active than the average American, they may get less exertion than a lot of blue collar workers in the U.S. They certainly are not the Oceanic equivalent of the Tarahumara Indians of Mexico (who tend to view marathons as sprints!). Clearly, exercise is not the chief reason why the Kitavans have superb vascular health.
Passwater: In any case-getting back to your comment about dementia-I think there is a sufficient number of elderly people in Kitava to judge whether senile dementia or heart disease would be a significant problem.
McCarty: Yes. And you don't need to have vast numbers of elderly to encounter dementia. I think I've read that about half of Americans over 85 suffer from dementia!
Passwater. That is scary.
McCarty: You bet it is. What's the point of taking elaborate measures to try to stay healthy into old age if your only reward is to live your last days in a totally dependent state of imbecility? It's so incredibly important to figure out how to prevent this outcome!
As I was saying, I was fascinated by the brief comment in Dr. Lindeberg's paper about dementia, and so I got his email address and wrote to him. I asked, "When you say you didn't see evidence for senile dementia, did this mean that you yourself didn't encounter any demented elderly people-or did you make some efforts to determine whether anybody on the island had ever heard of anyone who had become senile as a function of age?" He indicated it was the latter. He had attempted to determine whether anybody on the island had known about anyone else on the island who had become demented when they became old-and he learned that senile dementia was a totally foreign concept to the Kitavans!
Full-blown senile dementia in general is not a subtle disease. If a person cannot recognize his own children or the other members of his tribe, you would think that everybody would know that. Bear in mind that in Kitava, no one is distracted by a lot of information overload as we are in modern civilization. There, everyone's chief concern is about the other members of the tribe. That is what everyone knows more about than anything else. So, if a member of the tribe were to become severely demented, one would think that everyone would know about it. The bottom line is that no one in Kitava had ever heard of an elderly person becoming demented with age-which is quite a striking observation on an island which has about 2,500 residents and a fair proportion of the elderly, and where people can tell you about medical events that transpired a century ago!
I might add that, in response to his inquiries, the Kitavans introduced Lindeberg to a couple of mentally retarded people who were relatively young. This is not germane to senile dementia, but it shows that the Kitavans were trying to cooperate with his investigation.
When I learned about the evident rarity of dementia in Kitava, it jogged something in my memory, and I plowed back into the writings of Dr. Hugh Trowell. Dr. Trowell was a brilliant physician who worked in British East Africa during the middle decades of the 20th century. He wrote several books and monographs documenting the rarity of many "Western" diseases in Africa during the early decades of that century, when well trained British physicians had begun to serve the populace, but Western eating habits were only beginning to catch on among black Africans. Several of his later books were written in collaboration with Dr. Denis Burkitt. Many of our readers will remember them as the Burkitt and Trowell who popularized the health benefits of high-fiber diets.In any case, my old friend and mentor Herb Boynton loaned me several of Dr. Trowell's books-large portions of which I had read some years previously and I scanned their indexes for "senile dementia." I thus found a relevant passage in which Dr. Trowell cited the work of a British psychiatrist who had been practicing at the psychiatric ward of a Nairobi hospital back in the 1930s. From other portions of Dr. Trowell's book, I had learned that salt use was still uncommon among all but the most socially exalted black East Africans at the time. Further, I learned that stroke was considered extremely rare-rather like the situation that still prevails in Kitava. This psychiatrist wrote that on his psychiatric ward, he observed the full spectrum of psychiatric disorders that one would expect to encounter in Britain or the U.S.-with the exception that "senile dementia was a notable absentee."
So here, again, we have the correlation between a virtually unsalted diet, a virtual absence of stroke, and a virtual absence of senile dementia!
I am emboldened to suggest that if one keeps his or her cerebral vasculature so healthy as to be virtually immune from stroke, that individual also will be nearly immune from senile dementia-not just the so-called vascular dementia that results from small strokes, but from Alzheimer's disease as well. In effect, I am proposing that senile dementia is a disease of civilization made possible by salted diets!
Passwater: Tell us more about why you believe that this is the case.
McCarty: There is a lot of epidemiological evidence indicating that risk factors for stroke are very similar to risk factors for Alzheimer's. I am not the only scientist to have suggested that a healthy cerebrovascular endothelium may act in various ways to prevent the chronic inflammatory process that manifests as Alzheimer's disease, or to protect neurons from this process. One possibility, supported by some evidence, is that small strokes somehow act as a co-factor that makes Alzheimer's possible. If this is so, then preventing strokes also would tend to prevent Alzheimer's. Conversely, it is conceivable that vigorous cerebral blood flow is somehow protective.
Another possibility that I particularly like is that the nitric oxide produced by a healthy microvascular endothelium may have an anti-inflammatory impact on the brain -much as it does in preventing atherosclerosis in large arteries. Bear in mind that both Alzheimer's and atherosclerosis are low-grade chronic inflammatory disorders.
Additionally, in moderate physiological concentrations, nitric oxide might act to protect neurons from the pro-inflammatory factors that damage and kill them in Alzheimer's disease. Conversely, it is now known that the toxic amyloid peptides that seem to induce much of the neural damage in Alzheimer's, also attack the cerebrovascular endothelium and effectively block its production of nitric oxide. This suggests that, once the inflammatory process of Alzheimer's disease gains a firm foothold, there may be no going back, because the cerebrovascular endothelium won't be able to recover its healthful protective function. This further suggests that some measures which help to prevent Alzheimer's may not be of much use for treating it. In other words, don't wait until the horse is already out of the barn before shutting the barn door!
I probably should mention that some scientists speculate that excess nitric oxide production contributes to inflammatory damage in Alzheimer's-and I'm not sure they're wrong! You need to take a subtle look at this issue. In the modest concentrations produced by the healthy vasculature, and in the relative absence of the free radical superoxide, nitric oxide appears to have a number of protective properties, including an anti-inflammatory effect. On the other hand, in many inflammatory disorders, certain immune cells generate large amounts of nitric oxide in conjunction with large amounts of superoxide. These two compounds interact rapidly in a reaction that destroys the nitric oxide and converts it to a really vicious chemical known as peroxynitrite. So whether nitric oxide is helpful or harmful really depends on the context.
In any event, in light of my speculation that vascular nitric oxide might help to prevent dementia, I was particularly intrigued to encounter recent reports that people who use statin drugs to control their cholesterol levels appear to be at greatly reduced risk for Alzheimer's. A remarkable 70% reduction in risk has been suggested by two studies. Here is the relevance: there is now a lot of evidence that statin therapy lowers stroke risk fairly markedly. This initially seemed a little odd, because LDL cholesterol does not appear to be a strong risk factor for stroke. However, recent studies show that statins can act directly on the vascular endothelium to boost endothelial production of nitric oxide! Actually, there is both an increase in nitric oxide synthesis and a suppression of superoxide production.
As I just stated, superoxide is a potent free radical that can destroy nitric oxide, converting it to dangerous peroxynitrite. Increased effective production of nitric oxide offers a satisfying explanation for the ability of statins to prevent stroke but I suggest that this also may be the mechanism whereby they prevent Alzheimer's as well. Of course, I can't rule out the possibility that statins have some direct protective impact on brain tissue, but at least these findings are quite consistent with the possibility that the nitric oxide produced by healthy endothelium helps to prevent dementia.
Another measure which has been shown to boost the ability of vascular endothelium to produce nitric oxide is estrogen. This finding fits very nicely with the fact that there is considerable epidemiological evidence that women who use long-term postmenopausal estrogen replacement are at substantially lower risk for Alzheimer's!
However, the overriding determinant of cerebrovascular health may be dietary salt and potassium status. In other words, if you eat an unsalted, potassium-rich diet throughout life, chances are that you will have a healthy cerebral vasculature into ripe old age, and this will help you prevent not only stroke but, most likely, Alzheimer's disease. I realize that this is such an audacious proposition, it probably will be many years before we know just how accurate it is. It may be that the leanness and insulin-sensitivity of the Kitavans contribute importantly to their protection, too-as well as their intake of omega-3. Omega-3 has anti-inflammatory properties, and Alzheimer's is a type of inflammation.
Passwater: For the readers who may not have read part one of this series of columns, let's talk about why a potassium-rich sodium-reduced diet would result in the healthy endothelium that you were just speaking of.
McCarty: There is experimental evidence from laboratory rat studies that, in fact, salted diets tend to impair vascular nitric oxide production. Conversely, we know from rabbit studies that a modest increase in blood potassium levels-as can be achieved by eating more potassium tends to aid endothelial nitric oxide function by suppressing endothelial superoxide generation. This is much like what the statin drugs recently have been shown to do. One of the major determinants of these effects is the membrane potential of the vascular endothelial cells. When the membrane potential of endothelial cells is high, this tends to promote nitric oxide synthesis by boosting calcium uptake by the cells, while at the same time inhibiting the mechanisms that generate superoxide. More synthesis of nitric oxide and less of superoxide translates into a considerable boos in the protective activity of nitric oxide.
Passwater: But I thought that an increase in membrane potential helped to keep calcium out of cells!
McCarty: That is true in vascular smooth muscle and many other tissues but you see precisely the opposite effect in endothelial cells, for reasons that are a little too complex to discuss here. In endothelial cells, an increase in intracellular calcium levels is the signal that turns on nitric oxide production.
In any case, the salt and potassium contents of your diet influence the membrane potential of vascular endothelium and other cells by regulating the activity of the sodium-potassium pumps we mentioned earlier. When these pumps are vigorously active, membrane potential tends to increase, whereas you see the opposite effect if they are inhibited. A salted diet in susceptible people causes the body to make inhibitors of these pumps. This in turn helps the kidneys rid the body of excess salt, but at the cost of inhibiting the sodium-potassium pump in many other tissues.
Conversely, an increase in blood potassium levels directly stimulates the activity of these pumps- while helping the kidney to harmlessly rid the body of salt. The net effect is that membrane potentials tend to be high if one eats a low salt, high-potassium diet, whereas they are more likely to be low in the context of a salty, potassium-depleted diet. In torn, with a high membrane potential, the ability of nitric oxide to ward off blood clots, lower blood pressure, and quell inflammation and atherosclerosis is optimized, whereas a low membrane potential means that these benefits are substantially lost.
Note that the modulating effects of salt and potassium on cerebrovascular endothelial function don't necessarily correlate with blood pressure. In other words, if a salted diet doesn't raise an individual's blood pressure, that doesn't necessarily mean that it isn't impairing the healthful function of the cerebral circulation and increasing the risk for stroke. Conversely, getting more dietary potassium may protect one's brain even when it doesn't evidently improve his or her blood pressure.
By the way, one reason I think that leanness and excellent insulin-sensitivity might play a role in the protection from stroke and dementia enjoyed by the Kitavans is that the excessive fat exposure involved in insulin resistance syndrome can impair vascular nitric oxide function. This correlates nicely with the fact that insulin resistance syndrome increases risk for stroke.
I recently published a technical paper proposing that the key to avoiding strokes is to optimize the nitric oxide production of the cerebrovascular endothelium. I suspect that more and more factors that protect us from stroke-like statins, estrogen, a low-salt/high-potassium diet, leanness, and exercise-are going to be shown to have a favorable effect in this regard.
I also should mention that exercise training can boost endothelial nitric oxide production-as well as reduce stroke risk-while elevated homocysteine, associated with increased risk for both stroke and Alzheimer's, can impair endothelial function. There is a definite pattern here!
Passwater: One final question about the Kitavans. How can you be sure that these islanders don't just have some marvelous genetic inheritance that protects them from stroke and dementia? Could you be over-interpreting one rather anomalous observation?
McCarty: I can't know for sure, but I doubt that good genes alone are primarily responsible. Dr. Lindeberg met one Kitavan who had left the island as a young man and had lived a more Westernized lifestyle for a number of years. This individual, it turned out was both fat and hypertensive! Scientists repeatedly have noted that Oceanic cultures tend to be lean and relatively free of "Western" diseases while they maintain their traditional lifestyles, but that they rapidly become susceptible to obesity, hypertension, diabetes, and vascular disorders when they adopt a Westernized diet. Indeed, some of these cultures prove to be much more susceptible to these disorders than EuroAmericans are-particularly diabetes. The other reason I doubt it's purely a genetic issue is the admittedly thin evidence that senile dementia was very rare in Kenyans when they also were eating unsalted diets and were virtually free of hypertension and stroke.
I readily admit that my proposal that Alzheimer's may be substantially preventable by simple natural nutritional measures seems audacious, and this certainly will not be an easy proposition to prove. But my view is that you have nothing to lose by trying this strategy. Eating and exercising in a way that will keep blood pressure low and minimize risk for stroke, may or may not prevent Alzheimer's. But preventing stroke, vascular dementia, and other potentially devastating consequences of hypertension is no small benefit in itself! And the recent revelations about the apparent ability of statins, estrogen, and aspirin-like drugs (NSAIDS) to reduce Alzheimer's risk encourage the view that this disorder is indeed highly susceptible to prevention. If drugs have a protective effect, should we expect less of optimal nutrition?
By the way, I should note, in concluding, that Dr. Lindeberg has been very gracious and helpful to me, and I am particularly grateful for the fact that he sent me a copy of his fascinating Ph.D. thesis summarizing his research on Kitava. I hope that someday he will find the time to write his own book describing his experiences there.
Passwater: We thank you, and your co-authors, for bringing out this information about the importance of the dietary K Factor-the potassium-to-sodium ratio in the diet. You are making a significant contribution to overall health, as well as to the reduction of risk factors for the specific diseases that we have discussed. As I said at the start of this series, The Salt Solution is "must" reading for everyone. The book not only presents the scientific evidence, but provides a practical, easy-to-follow, nine-step nutritional program to improve eating habits and reverse the effects of typical high-salt diets. WF
© 2001 Whole Foods Magazine and Richard A. Passwater, Ph.D.
This article is copyrighted and may not be re-produced in any form (including electronic) without the written permission of the copyright owners.