Perspectives in Biology and Medicine

PERSPECTIVES IN BIOLOGY AND MEDICINE Volume 34 ¦ Number 2 ¦ Winter 1991 SALT IN HYPERTENSION—IMPORTANT TO CONTROL ORNOT? IRVINE H. PAGE* One of the good things about Perspectives is that it tolerates and often even invites opinion, and old age generates opinions. I have been asked for mine regarding the role of salt in causing arterial hypertension. If salt should be sharply reduced in the public's diet, it may be the next "big ticket" item in the government's adventures into medical education. The natural history of such educational episodes is a "consensus" meeting of "experts," followed by a blitz of celebrities from government, industry, and academe dispensing wisdom on the authority ofthe surgeon general et al. The most recent example is that of the "fatty alcohol" called cholesterol . It is bad for your arteries but still is the chemical basis for sex. Like cholesterol, salt is both bad and good. Lot's wife was turned into a pillar of salt for looking back, whereas Satchel Page wisely looked back "because something might be gaining on him." Before mechanical refrigeration many foods were preserved with salt. In my youth salt was even provided for cattle and horses, the so-called salt lick. The scientific literature on salt is so vast as to have become unmanageable . There are two exceptions: Derek Denton wrote a magnificent, comprehensive book, Hunger for Salt [1], and John Swales wrote his excellent Sodium Metabolism in Disease [2]. What is clearly established is that a moderate amount of salt [2-4 g.] is essential for health. Then comes the problem. Some people add salt to most things they eat and some don't. When some rats consume large amounts of salt, they de- *Address: Box 516, Hyannis Port, Massachusetts 02647.© 1991 by The University of Chicago. AU rights reserved. 0031-5982/91/3402-07l5$01.00 Perspectives in Biology andMedicine, 34, 2 ¦ Winter 1991 \ 159 velop hypertension; some do not. So: are there salt-sensitive rats and people and salt-resistant ones? Probably so, but their sensitivity is genetic , as first shown by Dahl [3] by breeding pure strains of salt-sensitive and -resistant rats. A subset of humans has yet to be identified, important as it is. The mechanism of the hypertension in salt-sensitive rats has not been established. It seems unlikely to me that hypervolemia is involved in the chronic phase of the hypertension as has been proposed. If it is, then it would not be a model for most patients with essential hypertension . A moderate intake of salt is essential for the good life. Too much is only for those who are born with the ability to cope with it. In short, then, there are salt-sensitive and -insensitive people, as shown by the appearance of hypertension. But salt intake is regulated in part by salt appetite that typically increases to satisfy an increasing desire for it. Much research has shown that salt is an important factor in many cases of hypertension. I have tried in an old-fashioned way to describe the mechanism in a book called Hypertension Mechanisms [4] which people may buy but seldom read. Now we come to the difficult problem of how much salt is enough or too much, and what people should do about it. The first big question is how to measure intake and output. Except in a metabolic ward it is difficult or impossible with most people. A diet history is all but useless, because most people cannot even remember what they ate yesterday, quite aside from having any idea how much salt was in the food and drink. Even tap water varies greatly in salt content, and when you add a margarita to it, or the cook adds a handful of something, the intake changes drastically. Even with labeling on the can or bottle giving the salt content per 1 00 grams or ounce, few know how to translate that into the amount consumed. The matter of collecting an accurate 24-hour urine specimen is also difficult and unreliable. Most people urinate directly after defecation, and that amount is surely lost to the measurement. Also, few healthy, vigorous persons can be bothered to...