Sodium intake and blood pressure in two Polynesian populations

Ageing in the South Pacific. Physical changes with urbanization

The process of ageing, the place the elderly hold in the South Pacific societies and the care they receive as they move from adult independence to geriatric dependence varies considerably in different Pacific Polynesian populations. This provides unusual opportunity to examine the physical changes of ageing in people of the same broad genetic make-up exposed to environmental changes brought about by urbanization. Epidemiological surveys carried out since 1962 among New Zealand Maoris, Tongans, Cook Island Maoris in Rarotonga and Pukapuka, and Tokelauans living in Tokelau and following migration to New Zealand, provide the main data base for this presentation. The pattern of blood pressure, body weight, serum lipids and clinical disorders show considerable variation which relate most closely to the adoption of westernized life-style and moving into an urban environment. Analysis of the ECG pattern, in Pukapukans, in whom blood pressure shows only a minor increase with age, compared with age and sex-matched subjects studied in Newcastle, England provide insights into the ageing heart. An examination of mortality based on risk factors at entry shows an inverse relationship of serum cholesterol to total mortality in New Zealand Maori men and women, in Tokelau men but not women. Increasing systolic blood pressure was related to mortality in New Zealand Maori men, Tokalau men and Caucasian women, but not in the other race sex groups. The pattern of ageing and risk factors must clearly be examined in individual populations because while death is the end the pathways vary.

Possible mechanisms of sodium-dependent hypertension: volume expansion or vasoconstriction?

A series of experiments was designed to explore the mechanisms contributing to hypertension caused by an acute or chronic sodium load. Acute salt-loading in totally or subtotally nephrectomized animals caused hypertension mediated partly through stimulation of excessive vasopressin release and partly through adrenergic stimulation. Chronic high-salt diet in rats submitted to partial nephrectomy, mineralocorticoid excess or one-kidney-one-clip renovascular hypertension caused blood pressure elevation mediated through a central neurogenic mechanism that could be reversed by administration of an inhibitor of phenylethanolamine-N-methyltransferase, the enzyme catalyzing conversion of norepinephrine to epinephrine. Thus, two vasopressor mechanisms were stimulated by sodium excess: an acute, transient, partly vasopressin-mediated phase seemed to be followed by a chronic phase mediated through stimulation of central sympathetic neurons. In neither phase was blood pressure related to intravascular fluid volume expansion.

Salt and blood pressure in Belgium

Blood pressure, pulse rate, body weight, and height were measured on two occasions in the inhabitants of a random 10% sample of households in a Belgian village. Twenty-four-hour urinary excretion of creatinine, sodium, and potassium was also determined. In subjects over the age of 19 there was a significant correlation for both systolic and diastolic pressure with age and body weight and, in women, also with pulse rate. After adjusting for these three variables, the systolic blood pressure in men was negatively correlated with the daily urinary potassium excretion, and the diastolic blood pressure in women negatively with the urinary sodium: creatinine ratio. The present data, obtained within one society, do not support a role for dietary sodium in the distribution of blood pressure within this population. Comparison of the present results with data from other countries does not refute the salt-genetic hypothesis but suggests also that a high potassium intake may lower blood pressure.

Etiology of essential hypertension

It is not possible to understand the etiology of hypertension without considering the role of inheritance. Epidemiological evidence indicates that the development of high blood pressure in the population at large depends on the interaction of different types of genes and several environmental influences. The sources of genetic variation in blood pressure distribution are polygenes, polymorphic genes, and dominant idiomorphic genes. The main environmental sources are weight gain, excess salt (Na) intake, and psychosocial stress. Only those individuals with a specific genetic predisposition may develop high blood pressure when exposed to excessive environmental influences.

Hypertension treated by sodium restriction

Forty-eight people with hypertension entered a controlled study to observe the effect of sodium (NaCl) restriction on blood pressure. In people with mild hypertension (diastolic blood pressure 90-105 mmHg), sodium restriction reduced blood pressure compared with a control group and 75% obtained a diastolic blood pressure of less than 90 mmHg. In people with more severe hypertension (diastolic blood pressure 4105 mmHg), sodium restriction achieved the same level of control as chlorothiazide (500 mg a day). Restriction of sodium intake is an effective method of reducing blood pressure and should be the first form of therapy in people with mild hypertension.

Blood pressure and diet in normotensive volunteers: absence of an effect of dietary fiber, protein, or fat

In the course of four controlled experiments on the effect of specific dietary components on cardiovascular risk factors, the effects on blood pressure of various sources of dietary fiber, of type and amount of dietary fat, and of animal versus plant were measured in young normotensive volunteers. In each of the four experiments a group of 50 to 75 healthy student volunteers received a control diet for 11/2 to 21/2 wk. They were then randomized into subgroups which received various test diets for periods ranging from 4 to 12 wk. In each experimental one group received the control diet throughout the whole experimental period. Diets differed between groups in one dietary component only. All foodstuffs were weighed out individually according to each person's energy needs. Body weights and Na intake were controlled. Initial blood pressures were about 120 mm Hg systolic and 70 mm Hg diastolic. Both systolic and diastolic blood pressure decreased during the test period in all four experiments on almost every diet, including the control diets, by about 0 to 5 mm Hg. However, changes in blood pressure over the test period were never significantly different between the test groups and the control groups. Thus, none of the investigated dietary factors had a demonstrable effect on blood pressure in young normotensive persons.

Racism, society, and disease: an exploration of the social and biological mechanisms of differential mortality

Racial differentials in mortality provide important insight into the nature of mass disease in capitalist society. Not only are the differentials sizable in magnitude, they are consistent for multiple causes of death and appear to evolve in response to social development. The relationships among social factors and the biological and physical agents of disease can be identified through racial contrasts and a pattern of causation which applies to both the minority and majority populations described. Furthermore, the impact of exploitation as the primary disease-mediating factor under capitalist social relations can be estimated. This paper attempts to combine an analysis of bio-medical mechanisms with Marxist social theory in a comprehensive framework for the study of the social origins of racial differentials.

Drinking water sodium and blood pressure in children: a second look

A previous study by the current authors demonstrated a statistically significant and clinically important elevation of 3-5 mmHg in mean systolic and diastolic blood pressure in high school sophomores in a community with 108 mg/L of sodium in the water supply when compared to their peers in an appropriately matched community with 8 mg/L of sodium. The current investigation, employing identical techniques but studying third graders in the same two communities, showed similar results. This second look considered dietary intake and urinary excretion of sodium. Since the difference in 24-hour dietary sodium consumption was 300 milligrams between the communities, an intake of one liter of high sodium tap water represented approximately 25 per cent of the difference in total sodium intake between the two communities. These studies suggest that sodium consumption in both drinking water and diet may be contributing to the different blood pressure distributions among the normotensive children in the two communities.

Is a circulating sodium transport inhibitor involved in the pathogenesis of essential hypertension?

There is controversy about the relationship between sodium intake and the prevalence of high blood pressure. Part of this controversy relates to how an increase in sodium intake could cause an increase in peripheral resistance. We have put forward the following hypothesis. In essential hypertension there is an inherited defect of the kidney's ability to excrete sodium which becomes increasingly obvious the greater the sodium intake. This difficulty in sodium excretion by the kidney increases the concentration of a circulating sodium transport inhibitor that affects sodium transport across many cell membranes. In the kidney the inhibitor adjusts urinary sodium excretion back towards normal so that sodium balance is near that of normal subjects on the same intake of sodium. In the arteriolar smooth muscle the inhibition of sodium transport across the cell wall causes a rise in intracellular sodium concentration which, in turn, raises the intracellular calcium concentration and thus increases vascular reactivity. This hypothesis also proposes that the abnormalities of sodium transport in circulating cells in vivo are directly due to the increased secretion of the circulating sodium transport inhibitor. Evidence supporting this hypothesis is discussed. Firstly, it is pointed out that there is much evidence which suggests that there is a circulating inhibitor of Na+-K+-ATPase, the level of which is related to sodium intake and that the level of this inhibitor appears to be increased in many hypertensives. Secondly, the finding that normotensive white cells incubated in the plasma of hypertensive patients develop the same decrease in the Na+-K+-ATPase dependent sodium transport as the hypertensives own white cells also suggests that hypertensives have an increase in a circulating Na+-K+-ATPase inhibitor.

Hormonal adaptation to the stresses imposed upon sodium balance by pregnancy and lactation in the Yanomama Indians, a culture without salt

The Yanomama Indians of northern Brazil and southern Venezuela have been identified as a "no-salt" culture. In this study, data were obtained to determine in this population the adjustments of sodium-related hormones to the stresses imposed upon sodium balance by pregnancy and prolonged lactation. Controls against the possibility that findings in the Yanomama were ethnic rather than dietary were provided by similar observations in the Guaymi Indians of Panama, who have free access to salt. Urinary concentrations of sodium were approximately 1 mEq/l in male and female Yanomama, with 24-hour excretion rates in the males averaging 1 mEq, similar to our prior observation. The pregnant Yanomama had exceeding high urinary concentrations of aldosterone. These were associated with higher plasma renin activities and serum aldosterone concentrations than in all other subjects. Although pregnant Guaymi had elevations of serum and urinary aldosterone, these were significantly lower (p < 0.001) than those of the Yanomama. Prolonged lactation in the Yanomama was associated with elevation of plasma renin activity and serum and urinary aldosterone concentration compared with the Guaymi, but were not higher than those in nonlactating Yanomama females. The findings suggest that pregnancy in a salt-poor environment is associated with an exaggerated augmentation of hormonal responses that enhance positive sodium balance.

Blood pressure and sodium balance in hypertensive patients in hospital

Ninety-one subjects with uncomplicated essential hypertension were admitted to hospital. They received a diet with a fixed amount of sodium (55 mmol/day), without calorie restriction. Blood pressure was measured at 2-hr intervals and averaged for each day. In patients who apparently adhered to a low salt diet before admission (group I), BP dropped 5 mmHg during the first 24 hr and then remained stable. In patients who previously ingested more salt (group II) a similar drop in pressure occurred during the first day, but pressure declined another 6 mmHg during the second day, to stabilize thereafter. Both neurovegetative and sodium-dependent factors appear to contribute to the decrease in BP while the patient is in hospital.

The association between urinary sodium excretion and blood pressure in children

This study explored the association between sodium excretion and blood pressure (BP). A new method was used to minimize the measurement error introduced by the large intrinsic variability of 24-hour sodium excretion. The ratio of intra- to interindividual variation was used to estimate the number of measurements needed to characterize the individual. When seven consecutive 24-hour samples were collected from 73 children, ages 11-14 years, a significant correlation between mean individual sodium excretion and BP was demonstrated. The independent relationship persisted when controlling for height, weight, pulse, age, sex and race (p = 0.045), but was eliminated by simultaneously considering mean creatinine excretion. Although the cross-sectional association described is quantitatively weak, a linear relationship between BP and sodium over the range consumed in this society could be important for prevention.

Dietary salt and hypertension

It has been argued that hypertension in developed countries is largely or wholly the result of excessive salt intake. As a result there are substantial pressures to reduce salt ingestion. Although it is likely that extreme salt restriction will lower blood-pressure, this is not a practical possibility. Evidence in favour of a more modest limitation of salt intake is conflicting and the possible harmful effects of salt restriction have not been assessed. Until more conclusive evidence is obtained it would be premature to advocate such massive public-health measures as reducing the sodium content of food.

Low salt diet and frusemide in the treatment of hypertension

The BPs of 86 of 100 severely hypertensive patients were controlled by measures designed to reduce total body sodium, namely a low salt diet plus the addition of incrementally increased frusemide treatment if diet alone was inadequate. Control of hypertension was maintained over prolonged periods of time in 70 of the patients. Among the 14 who failed to respond adequately, mean plasma renin level was higher (when tested) than in those who did respond adequately, and renal artery stenosis was discovered in 2. Supplementary propranolol controlled the hypertension in 8 of the inadequate responders.

Variability in 24-hour urine sodium excretion in children

How many 24-hour urine sodium measurements are adequate for characterizing a child's salt intake? Can overnight urine specimens accurately replace 24-hour collections for salt assessment? A sample of 73 6th-8th grade children was taken from two parochial schools in Chicago to investigate systematically these questions. Seven consecutive 24-hour-urine specimens were collected from each child. The estimated ratio of intra- to inter-individual variances was 1.94 for 24-hour-urine sodium. Based on this value, eight 24-hour specimens are necessary to limit to 10% the diminution of the estimated correlation coefficient between 24-hour-urine sodium and blood pressure. Six measurements are required to reduce to 0.01 the probability of misclassifying a child in tertile 1 versus tertile 3. The overnight specimens show a moderate consistency with the 24-hour collections in detecting children with high or low salt intake. For example 92% and 85% of children in the fifth quintile and the third tertile respectively of the true mean overnight sodium have their true mean 24-hour Na in the upper half of the distribution. These results suggest that in a large scale epidemiologic study, overnight specimens may be reasonable alternatives when 24-hour-urine sodium is practically very difficult to collect.

Can overnight urine replace 24-hour urine collection to asses salt intake?

Are overnight urine specimens adequate for characterizing the daily salt intake of individuals, i.e., can the overnight specimen replace the 24-hour specimen? Data from 142 male participants of an ongoing trial on the primary prevention of hypertension were used to examine this question with correlation analysis and quantile classification. Estimated correlation between the true mean 24-hour and the true mean overnight sodium excretion was 0.72. Furthermore, 67% of the individuals in the upper third of the distribution of true mean overnight urine sodium were also in the upper third of the distribution of true mean 24-hour sodium. Thus, these data are promising in regard to the use of overnight urine specimens for characterizing the salt intake of individuals. The number of overnight urine collections required to estimate accurately the correlation between an individual's true mean overnight urine sodium and a variable of interest (e.g., blood pressure) was calculated. Given the observed intra- and inter-individual variation, the data indicate that 14 measurements are needed to limit the diminution of the correlation coefficient to 10%.

Cardiac output and peripheral resistance in strains of rats sensitive and resistant to NaCl hypertension

The interrelationship of blood pressure, cardiac output, and peripheral resistance was studied in Dahl "S" and "R" rats after 3 days on a high (8%) NaCl diet. Both "S" and "R" rats were normotensive when fed a normal (0.3%) NaCl diet. After 3 days of the high NaCl diet, the "R" rats remained normotensive (BP 112 mm Hg), while the "S" rats had an elevation of arterial pressure (BP 133 mm Hg) (p less than 0.001). The cardiac outputs of both "S" and "R" rats were similar on the low NaCl diet. After 3 days of high NaCl feeding, the cardiac output of the "R" rats rose 18% above the "R" control level (p less than 0.0001), while the peripheral resistance declined 14% below the "R" control level (p less than 0.005), and the blood pressure (BP) did not change, a pattern quite contrary to the concept of "whole-body" autoregulation. With a similar 3-day high NaCl feeding in "S" rats, cardiac output (p less than 0.005) and peripheral resistance (p less than 0.05) both increased 10%, while BP rose 20%. After 7 days of high NaCl feeding, the cardiac output of the "S" rats had returned to normal, while blood pressure and peripheral resistance both continued to be elevated. This pattern of response in "S" rats could be compatible with the concept of "whole-body" autoregulation. However, since both NaCl hypertension and Goldblatt hypertension can occur in settings in which "whole-body" autoregulation appears not be to causally related, one cannot be certain whether "whole-body" autoregulation is playing a causal role in the mechanism of NaCl-induced hypertension in "S" rats. It is a striking dichotomy that 3 days of high salt feeding produces vasoconstriction in "S" rats and vasodilation in "R" rats.

The toxicity of salt

The subject of sodium toxicity has been controversial for a long time. There is no question that the element can be noxious when consumed acutely in large quantities and there is little doubt as to cause and effect Conversely the consequences of mederate chronic sodium consumption are much harder to document. The effects are insidious and are subject to modification by a variety of environmental influences such as dietary potassium. In addition most studies of chronic sodium excess have dealt with elusive subject of "essential" hypertension. Interpretations of data have been very difficult, and conflicting reports have occurred. Nevertheless epidemiological, clinical, and animal studies show that chronic excess sodium ingestion acting upon a substrate of genetic susceptibility, is an important etiologic factor in essential hypertension and the expression of its sequelae. Positive correlations have also have been obtained between dietary salt and the incidence of stroke and gastric cancer. Dietary potassium appears to confer some degree of protection from the toxic properties of sodium through some unknown mechanism. Available evidence indicates that a suitable intake of salt for man might be approximately 3.5 g/day and probably less. Salt consumption in most developed countries ranges between 8 to 40 g/day, and modern methods of food processing and preparation deplete the protective potassium. The incidences of hypertension in these countries range between 15 to 40% of their populations, and it exacts a dreadful toll. Recognition of the toxic properties of sodium and knowledge of the mechanisms involved in its toxicity offer great possibilities in the area of preventive medicine It may be possible by the sorting out of hypertension-prone subjects and dietary intervention to prevent or minimize the development of hypertension in susceptible individuals. This says nothing of other aspects of sodium toxicity, of which we are largely ignorant.

Hypertension treated by salt restriction

31 patients with a diastolic blood-pressure between 95 and 109 mm Hg have been treated for two years with a regimen involving a moderate restriction of salt in the diet. The results are compared with those in a control group and in a drug-treated group. Salt restriction has reduced the diastolic blood-pressure by 7.3+/-1.6 mm Hg, a result similar to that in patients treated with antihypertensive drugs. In the untreated group the diastolic blood-pressure rose by 1.8+/-1.1 mm Hg. Most patients did not achieve the desired amount of salt restriction and a stricter adherence to the diet might have caused further falls in blood-pressure. Excessive salt intake is probably a major cause of the epidemic of hypertension in "civilised" countries and a reduction in salt intake may help to control the epidemic. In persons with a diastolic blood-pressure between 90 and 105 mm Hg salt restriction should be tried before drugs.

The effect of high-sodium and low-sodium intakes on blood pressure and other related variables in human subjects with idiopathic hypertension

Nineteen patients with hypertension in whom all known causes of blood pressure elevation had been ruled out were classified as "salt-sensitive" or "nonsalt-sensitive" from the changes in blood pressure with changes in sodium intake from 9 meq to 249 meq/day. With the diet containing 249 meq sodium per day, there were no statistically significant differences in plasma sodium, potassium, chloride, aldosterone, cortisol or renin activity, or in urinary potassium, aldosterone or 17-hydroxycorticosteroids between the two groups. The "salt-sensitive" patients retained more sodium on the high-sodium diet than did the patients who were not sensitive to salt ("nonsalt-sensitive"); accordingly, sodium induced more weight gain in the salt-sensitive patients.

Urinary sodium, potassium and creatinine excretion in hypertensive and normotensive Australians

Studies were made in urine obtained from people attending for routine measurement of blood pressure in a screening programme. Subjects with diastolic blood pressure between 95 and 109 mm Hg excreted significantly more sodium than the group with diastolic blood pressure below 90 mm Hg. Urine volumes, potassium excretion and creatinine excretion did not differ significantly between the groups.

High sodium-low potassium environment and hypertension

The high sodium-low potassium environment of civilized people, operating on a genetic substrate of susceptibility, is the cardinal factor in the genesis and perpetuation of "essential" hypertension. The noxious effects begin in childhood, when habits of excess salt consumption are acquired at the family table, and are perpetuated by continuing habit and by increasing use of convenience and snack foods with artificially high concentrations of sodium and low levels of potassium. Present methods of food preparation leach out the protective potassium. Extradietary sodium chloride is a condiment not a requirement. Some primitive populations clearly preferred potassium chloride to sodium chloride. Chronic expansion of extracellular fluid volume induced by excess salt consumption causes the central and peripheral circulatory regulatory mechanisms to work at cross purposes, resulting in increased arterial pressure. The protective effect of potassium is dramatic and easily demonstrable in animals and man but its mechanism is not known. It cannot be entirely a direct effect on blood pressure because rats protected with extra potassium against a moderately high salt intake live much longer than control rats but have the same elevated blood pressures. In hypertension with a demonstrable "cause," the high sodium-low potassium environment makes a bad matter worse. In nature, feral man and his forebears were not confronted with excessive sodium and deficient potassium; indeed, the reverse was the case. Evolution has provided powerful mechanisms for conserving sodium and eliminating potassium, but no efficient physiologic mechanisms for conserving potassium and eliminating excess sodium. Most laboratory animal "control" diets contain an amount of sodium that fully suppresses aldosterone secretion, and the same is true of the "average" diet of the American people. Inadequate attention to dietary sodium and potassium makes many studies in both animals and man of uncertain validity. Internally, essential hypertension is an exceedingly complex mosaic of physiologic interactions. Viewed from outside, it is a disorder for which genetic material sets the stage; excessive sodium precipitates it and perpetuates it. Extra salt makes all forms more rapidly progressive and accelerates the onset of terminal events; extra potassium is everywhere protective. When an entire population eats excessively of salt, hypertension will develop among those genetically susceptible, but epidemiologic studies of salt versus blood pressure will not show a relation of salt to hypertension. This is the saturation effect. Low sodium diets are therapeutically effective but generally regarded as an impossible or an unnecessary nuisance. Effective prevention programs must be instituted at as early an age as possible. The efficacy of a prophylactic/therapeutic low sodium-high potassium diet should be weighed against the uncertain hazards of a lifetime of pill taking.

Salt, volume and the prevention of hypertension

The evidence supporting the thesis that hypertension can be prevented by eliminating salt from the diet is based on four principal sources: (1) epidemiological studies in unacculturated peoples showing that the prevalence of hypertension is inversely correlated with the degree of salt intake; (2) hemodynamic studies suggesting that the development of chronic experimental hypertension is a homeostatic response to a maintained increase in extracellular fluid volume (ECF); (3) evidence that the ECF of "salt eaters" is expanded in comparison to that of "no-salt eaters"; and (4) investigations in hypertensive patients receiving either diets greatly restricted in salt or continuous diuretic therapy which correlate the fall in blood pressure with a reduction in ECF. Although this mechanism of essential hypertension is still obscure the evidence is very good if not conclusive that reduction of salt in the diet to below 2 g/day would result in the prevention of essential hypertension and its disappearance as a major public health problem.

Gout in Maoris

Historical evidence suggests that the Maori people of New Zealand were virtually untroubled by gout or obesity at a time when these disorders, along with other elements of the gouty diathesis, were rife in the best fed and hardest drinking sections of the Northern European population. By the mid 20th century, however, the apparent decline of the gout in Europe and North America and the breakup of the gouty diathesis in those lands had been more than compensated by their large-scale reappearance in the Maori and in other indigenous inhabitants of the Pacific Basin who, at first sight, appeared to have become one large gouty family. Half the Polynesian population of New Zealand, Rarotonga, Puka Puka, and the Tokelau Islands proved to be hyperuricemic by accepted European and North American standards, the associated gout rate reaching 10.2% in Maori males aged 20 and over. The trends towards hyperuricemia and gout, on the one hand, and towards obesity, diabetes mellitus, hypertension, and associated degenerative vascular disorders, on the other hand, which manifest themselves separately in some Polynesian Pacific Islanders, run together in the Maori and Samoan people, presenting a combined problem of considerable importance to the public health. The appearance of these traits under conditions of plenty in the descendants of hardy and wide-ranging Polynesian voyagers, suggests the emergence of a formerly favorable ancestral polygenic variation through selection for survival under harder conditions. This may now have lost its primitive survival value with a paradoxic shift towards increased prevalence of obesity and the gouty diathesis in more affluent environmental conditions. This may now constitute a genetic load, with recent environmentally determined increase in morbidity and mortality rates from degenerative vascular disorders. There is no satisfactory evidence that overproduction of uric acid differs in mechanism from its European counterparts, although more work remains to be done to determine whether there is any difficulty in renal handling of an increased uric acid load. A high Maori morbidity rate from gout and morbidity and mortality rates from associated components of the gouty diathesis in the face of readily available skilled medical advice and care, indicate the need for greater future attention to help education and health care delivery, at least while conditions of plenty continue. Continuation of previous epidemiologic surveillance may then be required in order to provide a continuing index of the effectiveness of these measures, as well as an opportunity for further research into the interrelationships of these associated disorders.

Blood pressure, sodium intake, and sodium related hormones in the Yanomamo Indians, a "no-salt" culture

The Yanomamo Indians are an unacculturated tribe inhabiting the tropical equatorial rain forest of northern Brazil and southern Venezuela who do not use salt in their diet. The group therefore presented an unusual opportunity to study the hormonal regulation of sodium metabolism in a culture with life-long extreme restriction of dietary sodium, with parallel observations on blood pressure. Blood pressures increased from the first to second decade but, in constrast to civilized populations, do not systematically increase during subsequent years of life. In twenty-four hour urine collections on adult male Indians, excretion of sodium averaged only 1 plus or minus 1.5 (SD) mEq. Simultaneous plasma renin activities were elevated and comparable to those of civilized subjects placed for brief periods on 10 mEq sodium diets. Similarly, excretion rates of aldosterone equaled those of acculturated subjects on low sodium diets. The findings suggest that the hormonal adjustments to life-long low sodium intakes are similar to those achieved in acute sodium restriction of civilized man. Parenthetically, these elevated levels of aldosterone and renin were probably the norm for man during much of human evolution and suggest that the values observed in civilized controls are depressed by an excessive salt intake in contemporary diets.

Sodium restriction and thiazide diuretics in the treatment of hypertension

In a group of hypertensive patients it has been shown that moderate sodium chloride restriction has a hypotensive effect that is similar to that produced by thiazide diuretics. Blood pressure changed in relation to body weight in individual patients, and appeared to correlate with their sodium balance. The more a patient was depleted of sodium, the lower was the blood pressure. The serum potassium level fell with the use of thiazide diuretics, but in this group of patients there was little change in total body potassium content. The fall in serum potassium level appeared to relate to a shift into the cells due to the accompanying alkalosis. Potassium supplementation appeared to have had little effect and was unnecessary for most patients who were given diuretics for hypertension. Amiloride corrected the alkalosis and restored the serum potassium level to normal.

Antecedents of cardiovascular disease in six Solomon Islands societies

Cardiovascular risk factors have been analyzed as part of a combined ethnographic, anthropometric, and medical study of 1390 adult subjects in defined populations representing six Solomon Islands Societies. The six societies, all at low levels of acculturation, differed in habitat, way of life, and exposure to Western civilization. Criteria for ranking the societies in respect to acculturation were developed based on demographic changes within defined populations, secular increase in adult height, length and intensity of contact with Western cultural influences, religious belief, education, availability of medical care, economy, and diet. The six tribal groups were ranked by these criteria as follows: (1) Nasioi, (2) Nagovisi, (3) Lau, (4) Baegu, (5) Aita, (6) Kwaio. Physical health and nutrition were good in all six groups, and clinical evidence of coronary heart disease and atherosclerosis was absent. Serum cholesterol levels were higher at almost all ages and both sexes in the three more acculturated than in the three less acculturated groups. Serum uric acid levels were lower in the more acculturated than in the less acculturated groups. Among adult males in all groups, systolic blood pressure showed no age-related trend while diastolic blood pressure declined with age in the three less acculturated groups. Among adult females systolic blood pressure increased significantly with age in the three more acculturated groups but showed no age trend in the less acculturated. Weight declined with age in all groups. Analysis of electrocardiograms by the Blackburn method showed striking absence of codable abnormalities in all groups and a lower frequency of most abnormalities associated with coronary disease than in any population previously reported.

The differences in serum cholesterol and uric acid levels, and in intrapopulation trends of blood pressure in relation to age between the more and less acculturated groups were found to correlate best with dietary differences, especially in intake of salt, and of tinned meat and fish. The biologic differences noted may represent the earliest antecedents of cardiovascular disease in these societies.