Sodium intake and blood pressure in two Polynesian populations

Alpha-adrenoceptor properties in rat strains sensitive or resistant to salt-induced hypertension

Cerebral and renal alpha 2-adrenoceptors are implicated in the control of sympathetic activity and of sodium reabsorption respectively. In addition, sodium ions play an important role in the regulation of either alpha 2-adrenoceptor densities and affinities for adrenergic agonists. In the present study, alpha-adrenoceptor properties were investigated in genetically predetermined salt-sensitive and salt-resistant Dahl and Sabra rats. Cerebral alpha 2-adrenoceptor densities were higher in salt-resistant than in salt-sensitive Dahl and Sabra rats. In contrast, renal alpha 2-adrenoceptor density was higher in salt-sensitive than in salt-resistant rats. No difference in cerebral and renal alpha 1-adrenoceptor densities was observed between Dahl and Sabra substrains. Noradrenaline content in cerebral and renal cortex were also similar in both these rat substrains. Sodium ions markedly increased cerebral and renal high-affinity alpha 2-adrenoceptor densities in salt-sensitive but not in salt-resistant rats. Cerebral and renal alpha 1-adrenoceptor densities were unchanged in salt-sensitive and salt-resistant substrains of Dahl and Sabra rats. In addition, sodium ions reduced the affinity of adrenaline for renal alpha 2-adrenoceptors in salt-sensitive rats but not in salt-resistant rats. We can conclude that there exist genetically determined differences in the densities and properties of cerebral and renal alpha 2-adrenoceptors between salt-sensitive and salt-resistant rat strains. Abnormal densities of alpha 2-adrenoceptors may play a primary role in the role in the development of hypertension in salt-sensitive animals. These results also suggest an association between absence of sodium regulation of alpha 2-adrenoceptors and resistance to salt-induced hypertension. The absence of sodium regulation in salt-resistant rats may be linked either to a particular receptor conformation or to an abnormal structure of the receptor system. This property may represent a genetically-mediated change responsible for the resistance to the development of salt-induced hypertension.

Blood pressure changes with age in two ethnic groups in Fiji

Blood pressure was studied in urban and rural samples of the Melanesian and Indian populations of Fiji during a National Cardiovascular Disease and Diabetes Survey in 1980. Mean blood pressures rose with age and tended to be higher in urban than in rural populations, particularly in the middle age range. There was no clear or significant difference between the ethnic groups. When the prevalence of hypertension was studied (using WHO criteria) similar age, geographic and ethnic differences were found. Comparisons with data from 1960 revealed no significant change in mean blood pressures during the 20-year interval. Rural populations were leaner and appeared to consume less salt than did urban groups. There were positive and significant correlations between blood pressure and triceps skinfold thickness in most subgroups.

Corcoran lecture: the case for or against salt in hypertension. Arthur Curtis Corcoran, MD (1909-1965). Tribute and prelude to Corcoran Lecture of 1988

Salt intake in excess of body needs has long been considered a factor in the genesis and maintenance of human hypertension; the mechanism is salt retention due to faulty renal excretory efficiency. This discussion reviews clinical studies that make a case either for or against the salt hypothesis. Included is a summary of recent experiences with 4 days of salt depletion and 3 days of salt loading in 96 normotensive control subjects and 40 hypertensive patients. These studies were done to test the hypothesis that salt-sensitive blood pressure changes are quantitatively related to sodium balance. However, we found no statistically significant relation between arterial pressure changes and sodium lost during salt depletion or retained during salt loading. The failure of that hypothesis prompted a study of the known factors that control arterial pressure by using multidimensional response surface modeling for changes produced by salt loading. The analysis indicated that in these experiments salt-sensitive blood pressure changes of hypertensive patients were controlled differently than those of normotensive subjects. In the hypertensive group, the changes were highly predictable by combinations of variables, which featured plasma aldosterone, norepinephrine, and epinephrine. In the normotensive group, the changes were less predictable; fewer of the factors were involved, and plasma renin activity was the featured variable. These findings and results of studies done over the past 50 years indicate that salt-dependent hypertension is controlled by many factors and is not a strict correlate of salt intake.

A cross-sectional ecological analysis of blood pressure and its determinants in eleven Pacific populations

A cross-sectional interpopulation analysis of blood pressure and its determinants was conducted with the data collected during epidemiologic surveys in 11 Pacific island populations from 1975 to 1981. In each of these populations, the mean arterial blood pressure increased with age; the overall blood pressure levels differed among the populations. The multivariate analyses suggest that dietary factors that result in differences in body mass, plasma cholesterol, and glucose intolerance contribute considerably to interpopulation differences in blood pressure. The impact of these differences in effects of dietary factors on interpopulation blood pressure seemed to be uniform, even though the overall levels of each of these three variables differed significantly among the populations. This study of blood pressure data, accrued from 6224 men and 7029 women aged 20-79 years, supports the hypothesis that dietary factors strongly contribute to high blood pressure as well as to interpopulation differences in the prevalence of hypertension. We propose using these data in planning programs for prevention and control of hypertension in the Pacific countries.

Central sympathetic stimulation produced by saline application into the nucleus tractus solitarii area of conscious rats

Hypertonic saline 4% was microinjected into the area of the nucleus tractus solitarii (NTS) of conscious rats. The experiments were designed to explore the systemic hormonal responses and the contribution of various hormones to the hypertensive effect elicited by this procedure. A mean blood pressure rise to 155 +/- 3 mmHg (as compared to 119 +/- 2 in rats receiving the same volume of equiosmolar dextrose solution, P less than 0.05) was accompanied by significant rises in plasma norepinephrine (0.556 +/- 0.128 ng/ml) and epinephrine (0.970 +/- 0.287 ng/ml) as compared to control rats receiving dextrose or control rats having only the cannula implanted, without microinjection. There was no significant change in plasma renin activity or plasma vasopressin levels, and the blood pressure rise could not be prevented or reversed by an angiotensin-converting enzyme inhibitor. The data are consistent with the hypothesis that the hypertensive response to this procedure is mainly due to an acute stimulation of central sympathetic neurons.

Blood pressure in British children: associations with adult blood pressure and cardiovascular mortality

Blood pressure was measured in 4186 children aged 5 to 7 years in 9 British towns. 3 towns had high, 3 had intermediate, and 3 had low adult blood pressure levels observed in an earlier study of middle-aged men. Significant differences between the towns were found for the children's mean systolic blood pressure (range 96.7 to 102.4 mm Hg) and diastolic pressure (range 55.9 to 60.3 mm Hg). The pattern of systolic blood pressure differences in children was similar to that observed in the study of middle-aged men (r = 0.65). The town mean systolic pressures in children show an association with standardised mortality ratios for cardiovascular disease in adults. The pattern of geographical differences in blood pressure observed in British adult men may have its origins early in life.

Incidence of hypertension in the Framingham Study

Incidence and trends in incidence of definite hypertension were analyzed based on 30 years follow-up of 5,209 subjects in the Framingham Heart Study cohort. Based on pooling of 15 two-year periods, hypertension incidence per biennium increased with age in men from 3.3 per cent at ages 30-39 to 6.2 per cent at ages 70-79, and in women from 1.5 per cent at ages 30-39 to 8.6 per cent at ages 70-79. No consistent trend in incidence rates was evident for either sex from the 1950s through the 1970s. The proportion of hypertensive subjects receiving antihypertensive medication has increased since 1954-58 and exceeded 80 per cent for both men and women ages 60-89 years in 1979-81. Incidence data presented in this report may serve as a baseline for assessing the impact of future public health efforts in the primary prevention of hypertension.

Lifestyle and blood pressure levels in male twins in Utah

Healthy male monozygotic (MZ) and dizygotic (DZ) twin pairs (MZ pairs = 77; DZ pairs = 88) were studied to assess the effect of dietary intake, physical activity, physical fitness, body mass index (BMI), sum of the triceps and subscapular skinfold measurements, alcohol and caffeine consumption, and smoking patterns on blood pressure. Data on physical activity, detailed dietary intake, medical history, and demographics were obtained from a questionnaire. A bicycle ergometer was used to estimate level of fitness; other medical information was ascertained from physical examination. After normalizing the study variables, intraclass correlations for BMI and the sum of the triceps and subscapular skinfold measurements were higher in MZ than in DZ twin pairs (BMI: MZ r = 0.76, DZ r = 0.48; skinfolds: MZ r = 0.73, DZ r = 0.28), as were VO2max(MZ r = 0.63, DZ r = 0.25) and post-bike heart rate (MZ r = 0.69, DZ r = 0.19). Both systolic (SBP) and diastolic blood pressure (DBP) had high heritability estimates (SBP = 0.60, and DBP = 0.66). Using factor analysis, four major lifestyle factors were identified and categorized as: 1) dietary intake; 2) a factor heavily weighted by cigarette smoking, alcohol and caffeine consumption; 3) fatness; 4) physical activity and physical fitness. Adjustment for these factors did not alter heritability estimates for either SBP or DBP.

Stress, salt and hypertension

Reasons are given why calcium, obesity and genetics cannot be considered primary factors in the etiology of essential hypertension. This leaves the major protagonists as salt and neuroendocrine responses to the emotions aroused by the social environment. Most essential hypertension is renin dependent and associated with the physiological changes induced by arousal of the defence response. The psychosocial stimulation associated with this arousal induces an increase in salt appetite. This makes the salt consumption of society a measure of the social stress to which it is exposed. Primitive people whose blood pressure remains normal throughout their lives may lack modern societies' physically protective achievements but their religiously prescribed social solidarity may protect them from psychosocial stress. Our chronic suppression of awareness of emotional arousal together with loss of the ritualized support of affiliative behavior may result in repressed emotional responses which find somatic expression in diseases such as essential hypertension. Hypertensiologist George Pickering proposed that the primitive's ritual and taboo (the equivalent in our society might be the Alcoholic's Anonymous belief in a 'Higher Power') protect them from much anger and despair. He gave this precedence over salt as the primary factor in essential hypertension. New evidence supports this. Despite a high salt diet the blood pressure of socially adjusted rodents remains normal throughout their lifespan. On the other hand, the hypertension that develops when they are psychosocially stimulated is not abated by a low salt diet. In humans, the blood pressure of cloistered, secluded Italian nuns on a high salt diet has remained normal for 20 years while that of nearby village women has risen at a startling 2 mmHg/annum during the same period. On the other hand, in rapidly changing Malawi mature adult, rural and urban blood pressures are rising fast despite a low salt intake. Thus the evidence today argues that the most important factor in the etiology of essential hypertension is not salt but psychosocial stimulation.

Cations and hypertension: sodium, potassium, calcium, and magnesium

The association between sodium intake and hypertension has been studied for almost a century. More recently, it has been suggested that abnormalities in dietary intake of potassium, calcium, and magnesium may play a major role in the pathogenesis of hypertension. A critical analysis of selected data from animal and human studies is discussed.

Hypertension and indicators of coronary heart disease in Wallis Polynesians: an urban-rural comparison

A comparative study of hypertension, and indicators of and risk factors for coronary heart disease was undertaken in samples of rural Wallisians of Wallis Island, and first generation Wallisian migrants in the urban centre of Noumea, New Caledonia. Approximately 20% of the adult population of the two communities was included in the study. Higher mean blood pressure and hypertension prevalence in Wallisians in Noumea compared to those in Wallis was documented. There was no significant rise in blood pressure with age in rural Wallisian males. Wallisians in Noumea tended to be more obese than those in Wallis (particularly females). Although differences in the extent of obesity appeared to explain some of the differences in blood pressure between populations of Wallis and Noumea, other environmental factors (such as salt intake) are probably important. There was a trend for a higher prevalence of Q wave changes on the ECG in urbanized Wallisians compared to their rural counterparts. There was no significant or consistent differences in plasma lipid concentrations between the two groups. The prevalence of diabetes was 7 and 4 times higher in Noumea compared to Wallis for males and females respectively. Differences in diabetes and hypertension prevalence are more likely to account for the variation in ischaemic heart disease than plasma lipid levels.

Double-blind, placebo-controlled trial of potassium chloride in the treatment of mild hypertension

Epidemiological and experimental data suggest blood pressure-lowering effects of dietary potassium. A randomized, double-blind clinical trial was used to assess blood pressure response to orally administered potassium, 120 mEq/day, and to placebo in 101 adults with mild hypertension. Blood pressure was measured with a random-zero sphygmomanometer every 2 weeks of this 8-week trial. Systolic blood pressure in the potassium-treated group decreased by 6.4 +/- 13.7 (SD) mm Hg (p less than or equal to 0.025) compared with 0.11 +/- 13.0 mm Hg in the placebo-treated group (p = 0.96). Diastolic blood pressure in the potassium-treated group decreased by 4.1 +/- 8.3 mm Hg (p less than or equal to 0.05) compared with a 1.6 +/- 6.5 mm Hg decrease in placebo-treated subjects (p = 0.09). Baseline blood pressure of potassium-treated subjects was unexpectedly higher than that of controls. After correcting for baseline variation, blood pressure still decreased 3.4/1.8 mm Hg more in potassium recipients than in placebo recipients (p = 0.14 and 0.24, respectively). Blood pressure decreased by 19/13 mm Hg in five blacks taking potassium versus a 1/0 mm Hg increase in seven blacks taking placebo. Compliance with the potassium regimen was 91.5% by pill count; only one subject discontinued treatment because of side effects. In conclusion, 120 mEq/day of microencapsulated potassium chloride was well tolerated in adults with mild hypertension. An antihypertensive effect of potassium cannot be ruled out despite the fact that there was no statistically significant difference between potassium-treated and placebo-treated subjects after adjustment for differences in baseline blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Geographical distribution of cerebrovascular disease mortality and food intakes in Japan

The present study focuses on an analysis of the relationship between cerebrovascular disease mortality and food intake. For this purpose, standardized mortality ratios(SMRs) from cerebrovascular disease were calculated for 3341 basic administrative units (wards, cities, towns and villages) between 1969 and 1978 in Japan. The major nutrient intakes and 30 selected food items were obtained from the 1974-1974 Ministry of Health and Welfare, National Nutrition Surveys in 1040 randomly sampled census tracts in 600 areas (18% of the nation). Our analysis demonstrates that the geographical pattern of cerebrovascular disease SMRs in Japan vary from higher in East Japan to lower in the West, and higher in the less urbanized areas, and lower in the more urban ones. Foods positively associated with cerebrovascular disease were rice and other starchy foods, pork, algae (seaweed), and salty foods such as miso (soybean paste), pickled vegetables, soy sauce and salted fish. All of these foods, with the exception of pork, are part of the traditional Japanese diet. On the contrary, mortality was negatively associated with intakes of wheat, butter and margarine, beef and eggs, items considered to be representative of a European diet. Using a stepwise multiple regression analysis, miso and salted fish were selected as positive, and beef and eggs as negative correlates of cerebrovascular disease mortality. According to these results, it is suggested that these four foods are useful as negative and positive indicators of improvement in dietary intakes as related to the reduction in the occurrence of cerebrovascular disease.

Urinary and serum electrolytes in untreated black and white hypertensives. Veterans Administration Cooperative Study Group on Antihypertensive Agents

Twenty-four hour urinary excretion of sodium (Na), potassium (K), Na/K ratio and creatinine (Cr), serum Cr, Na, and K, and plasma renin activity (PRA) were evaluated in 623 untreated hypertensive men. Blacks (n = 407) and whites (n = 216) were similar in weight, heart rate, systolic blood pressure (SBP), diastolic blood pressure (DBP), 24-hour urine Cr excretion, and Cr clearance. Twenty-four hour urine Na excretion was the same in blacks and whites, but whites excreted 62% more K than blacks: 73 +/- 41 (mean +/- SD) vs 45 +/- 40 mEq/24h (p less than 0.001). Urinary Na/K ratio was 4.51 +/- 2.18 in blacks and 2.85 +/- 1.40 in whites (p less than 0.001). Serum K and PRA were also lower in blacks. Serum and urine Na/K ratios, serum Na and age were positively associated with SBP; serum K and PRA were negatively associated with SBP. Serum Na/K ratio, heart rate and weight were positively associated with DBP; serum K was weakly negatively associated with DBP. The racial difference in urinary K excretion and serum K is believed to reflect a difference in dietary K intake between blacks and whites. This difference may be an important factor in the greater prevalence of hypertension among blacks.

The relationship of salt intake and arterial blood pressure in salted-tea drinking Kashmiris

In this study we attempted to explore the relationship between salt and blood pressure in a salted-tea drinking population of Northern Kashmir which has not been exposed to a Western way of life. All the available family members of randomly selected houses in 14 villages were studied. Dietary intake was documented for the whole month of the study period to estimate the daily salt consumption in 281 subjects (193 males, 88 females), whose ages were reliably known. Their age ranged from 15 to 85 years (median 35) and their mean daily salt intake was 150 +/- 52 mmol (range 80-440). Both the systolic and diastolic blood pressures showed a significant increase with the salt intake and age; multiple regression analysis suggested an independent effect of salt intake on blood pressure after adjusting for age. Twenty-six subjects (9.3%) had hypertension (blood pressure greater than or equal to 160/95 mm Hg); their daily salt intake was significantly higher than that of normotensive subjects (mean 167 +/- SD 53 vs 142 +/- 46 mmol; P less than 0.001). These studies suggest a relationship between habitual high salt intake and blood pressure.

Changes in central alpha-adrenoceptors and noradrenaline content after high sodium intake in Sabra salt-sensitive and salt-resistant rats

Several studies have suggested a correlation between sodium accumulation and the development of hypertension. However, the mechanisms whereby sodium is able to increase blood pressure remain unclear. In the present study, alpha-adrenoceptors and noradrenaline contents have been studied in the cerebral cortex, hypothalamus and medulla oblongata in the Sabra rat strain in order to define their role in the resistance or sensitivity to sodium-induced hypertension. Alpha-Adrenoceptors were defined using the selective ligands 3H-prazosin and 3H-rauwolscine for alpha 1- and alpha 2-adrenoceptors, respectively. Under normal sodium diet, alpha 2-adrenoceptor density was higher in cerebral cortex and lower in hypothalamus and medulla oblongata of SBN (salt-resistant) compared to SBH (salt-sensitive) rats. Five weeks of high sodium intake induced a decrease in alpha 2-adrenoceptor density in cerebral cortex and an increase in hypothalamus only in SBN rats. These changes abolished the differences between SBH and SBN rats observed with a normal sodium diet. No changes in density and affinity of alpha 2-adrenoceptors were observed in medulla oblongata of SBN and SBH rats. Density and affinity of alpha 1-adrenoceptors were similar in SBN and SBH rats in all the tissues studied and they were unaffected by the high sodium diet. Noradrenaline contents in cerebral cortex, hypothalamus and medulla oblongata were also similar in the two rat substrains under normal sodium diet, but high sodium intake induced a decrease cerebrocortical noradrenaline content only in SBN rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonpharmacological approaches to the control of high blood pressure. Final report of the Subcommittee on Nonpharmacological Therapy of the 1984 Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure

This report reviews a variety of nonpharmacological approaches used to control arterial blood pressure. Of all the modalities considered, only three had sufficient scientific support to warrant recommendation for inclusion in hypertension treatment programs. Each of these three modalities--weight control, alcohol restriction, and sodium restriction--was found to be capable not only of independently controlling blood pressure (particularly in patients with mild hypertension) but also of reducing the number and dosage of prescribed pharmacological agents, should their prescription be indicated. Weight reduction was found to reduce the risk from elevated arterial pressure as well as overall cardiovascular morbidity and mortality. However, because the rate of recidivism was exceedingly high in these studies, close and continuous patient follow-up is considered necessary. Excessive alcohol intake is associated in many studies with proportionally higher arterial pressures and an increased prevalence of hypertension. Therefore, the recommendation of moderation in alcohol consumption to less than 2 oz of ethanol daily for patients with hypertension is supported. Restriction of dietary sodium to less than 2 g/day was the only other nonpharmacological approach with sufficient support to be recommended as a treatment for hypertension. Although long-term studies are sorely lacking, sodium restriction has been shown to be manageable and safe and probably will benefit those hypertensive patients who are sodium-sensitive.

Improved arterial distensibility in normotensive subjects on a low salt diet

Arterial pulse wave velocity (PWV), a noninvasive index of arterial distensibility, was measured in 57 normotensive subjects who followed a voluntary low salt diet for a period ranging from 8 months to 5 years (mean, 24.8 months). Subjects who followed a regular diet were matched for age and mean arterial pressure with the low salt (LS) sample and were used as controls (C). For both samples, subjects were divided into three age groups: Group 1 (aged 2 to 19 years, n = 16), Group 2 (29 to 44 years, n = 26), and Group 3 (45 to 66 years, n = 15). There was a marked increase in aortic PWV with age in the control sample but not in the LS sample. There was no significant difference in aortic PWV for Group 1, but in Groups 2 and 3, the LS subjects showed a decrease of 21.8% and 22.7%, respectively, compared to C subjects. Aortic PWV (cm/sec) was: Group 1: C = 581 (SE44), LS = 614 (SE31); Group 2: C = 942 (SE46); LS = 737 (SE27) (p less than 0.001); Group 3: C = 958 (SE77), LS = 741 (SE25) (p less than 0.05]. Arm and leg PWV were also significantly lower in the older age groups. These findings suggest that normotensive adult subjects who follow a low salt diet (mean intake, 44 mmol Na/24 hours) have reduced arterial stiffness and that the effect is independent of blood pressure. This is prima facie evidence that reduced salt intake has a beneficial effect in improving distensibility of the central aorta and large peripheral arteries, which is independent of its antihypertensive action.

Factors that determine the response of people with mild hypertension to a reduced sodium intake

One hundred and eighty-six males who had had 3 run-in visits entered the study with a supine diastolic BP 95-110 mm Hg. This was followed by 3 pretreatment and 3 post-treatment visits. One hundred and sixty patients were given advice to reduce sodium intake after visit 3, and twenty-six patients served as control. In the control group there were relatively insignificant changes between the pre and post visits. In the diet group blood pressure fell by 13/9 mm Hg; urine sodium from 168 to 85 mmol/day and plasma renin activity rose from .50 to .77 ng AI/ml/h. Regression analysis showed that the only cross-sectional correlations were PRA with age, urine sodium and plasma potassium. There were highly significant correlations between the change in urinary sodium and the change in blood pressure and between the changes in blood pressure and plasma renin activity. Multiple Regression Analysis indicated that the final diastolic blood pressure achieved depended upon the initial diastolic blood pressure, the fall in sodium intake, and was reduced by the rise in plasma renin activity. Patients who responded to sodium restriction had a lower initial renin value than other patients. This study emphasises the importance of the interaction between sodium, potassium and renin in the determination of blood pressure levels.

Migration and biocultural adaptation: Samoans in California

The consequences of migration for the Samoan population of California are discussed within the context of other studies focusing on Samoan native and migrant populations in Samoa and Hawaii. The social, cultural and economic characteristics of California Samoans are described and data are presented for body morphology, blood pressure, psychosocial stress and social support, general morbidity patterns and mortality rates for 1978-1982. Although the nature of disease risks appear profound in this population, particularly patterns of extreme obesity and psychosocial stress, mortality rates for heart disease and stroke are less than might be expected among other American groups. Such unexpectedly low mortality rates may represent the relatively healthy experience of older cohorts of migrants, or be a result of proportionally few individuals having lived long enough in California to develop cardiovascular and other chronic disease that have lengthy natural histories. We postulate that at present Samoan social structure, particularly the high status that accrues with aging in traditional Samoan society, may act as a buffer for the risk factors we observed and their expected outcomes. If so, the U.S.-born Samoans who are currently passing through childhood and early adult years with progressively less awareness of Samoan values of family and social structure will exhibit the same risks we describe here, but lack the available social buffers that currently exist for their parents.

Determination of blood pressure in children

The present paper reviews the epidemiologic patterns of blood pressure in children by demographic variables such as age, race, sex, education and social class. Other possible determinants for high blood pressure in both adults and children are also discussed, including obesity and salt intake. Special attention is given to the phenomenon of tracking and to genetic influences in blood pressure, the latter discussed in the context of the strengths and limitations of twin and familial aggregation studies.

Dietary sodium and arterial blood pressure: evidence against genetic susceptibility

Thirty five subjects with both parents in the top third of their age specific blood pressure distributions and 31 subjects with both parents in the bottom third of their blood pressure distributions restricted their intake of sodium for eight weeks while taking part in a double blind, randomised crossover trial of supplements of sodium and placebo. A comparison of two periods of four weeks at different intakes of sodium showed no differences in blood pressure in either the groups as a whole or the subgroups who complied best with the diet and tablets. In the compliant subgroups mean urinary sodium excretions were above 120 mmol(mEq) and below 50 mmol/day. The study provides evidence against the hypothesis that people with a family history of high blood pressure are more susceptible in their blood pressure response to dietary sodium.

Sodium is more important than calcium in essential hypertension

There is much circumstantial and some direct evidence in humans to suggest that a high consumption of salt predisposes communities and individuals to the development of essential hypertension. Recent work has suggested possible mechanisms whereby a high salt intake could cause a rise in blood pressure in genetically susceptible persons. Restriction of salt intake in the diet lowers blood pressure in many subjects with high blood pressure and this fall in blood pressure is mediated in part by a diminished renin response to sodium restriction as hypertension develops. The effect of sodium restriction, like diuretics, is additive to most blood pressure lowering drugs, particularly those that inhibit the renin system such as beta-blockers and angiotensin converting enzyme inhibitors. Claims that a slight reduction in calcium intake may be important in the development of high blood pressure are disputed. Furthermore, no satisfactory hypothesis has been put forward to explain how a small reduction in dietary calcium intake could cause high blood pressure. Large increases in calcium intake have been reported to lower blood pressure in both normotensive and hypertensive humans. The three published studies, however, are not in agreement.

Is calcium more important than sodium in the pathogenesis of essential hypertension?

The hypothesis that abnormalities of calcium homeostasis at both an organ and cellular level are a primary factor in the pathogenesis of human and experimental hypertension forms the basis of this review. The rapidly expanding data base relating disordered calcium metabolism to altered vascular smooth muscle function and increased peripheral vascular resistance is summarized and integrated with the observations that reduced dietary calcium intake is the most consistent nutritional correlate of hypertension in the United States. The role of sodium and sodium chloride in pathogenesis of hypertension is reassessed in the light of new data from epidemiological clinical research, experimental models, and cell physiology investigations. The data supporting the thesis that the effects of sodium or chloride or both on blood pressure may represent, in selected situations, secondary influences mediated through induced changes in calcium homeostasis are presented. The interface between these nutritional factors and the normal regulation of vascular smooth muscle is discussed, providing a theoretical framework in which to assess the current information and to formulate the necessary future research.

Monovalent and divalent cations in hypertension

The relationship of four cations (sodium, potassium, calcium, magnesium) to hypertension is reviewed. It seems reasonable to advise some reduction in sodium intake, and an initial goal of a mean intake of 120 mmole per day for men and 90-100 mmole per day for women is suggested. Some increase in potassium intake may well be justifiable but is better achieved through potassium-containing foods than by any artificial supplements. The data for calcium and magnesium are not sufficiently strong to warrant any recommendation for a change in intake at present.

Group comparisons of blood pressure and indices of obesity and salt intake in Pacific populations

Group comparisons of blood pressure and indices of obesity and salt intake from epidemiological studies conducted in the Pacific early in the 1980s are presented. The comparisons were of a rural-urban type, and showed a trend for a lower prevalence of hypertension and for lower mean blood pressures in adults from rural areas, compared with urban populations. Rural residents were also slimmer and appeared to have a lower salt intake than did urban dwellers. These findings give possible support to the role of adiposity and salt intake in the genesis of essential hypertension.

Hyperlipemia and arteriosclerotic cardiovascular disease in the Polynesian population of Rarotonga

Total cholesterol, total triglyceride and high density lipoprotein (HDL) cholesterol and their relation to arteriosclerotic cardiovascular disease (ASCVD) were investigated in a population of Polynesian Maoris in Rarotonga who are becoming increasingly westernized. 8.5% of the population had plasma triglyceride elevations (triglyceride greater than or equal to 200 mg/dl), and the occurrence of hypertriglyceridemia was significantly higher in males than females. 5.8% of the population had elevations of total cholesterol (cholesterol greater than or equal to 250 mg/dl), and the proportion with elevation of total cholesterol was similar for males and females. 3.2% of the population had elevations of both triglyceride and cholesterol. HDL cholesterol concentrations were relatively low, and no sex differences were observed at any age. Analysis of lipoprotein cholesterol and triglyceride in a subset of those who had hyperlipemia indicated that the elevations of total cholesterol and triglyceride were mainly due to elevations of low density lipoprotein (LDL) cholesterol and very low density lipoprotein (VLDL) triglyceride, respectively; furthermore, elevations of VLDL triglyceride and LDL cholesterol were significantly correlated with increase in VLDL apolipoprotein B (apo B) and LDL apo B, respectively. Although an appreciable prevalence of diabetes was observed in this population (male: 6.7%, female: 8.4%), the diabetes could not account for the hyperlipemia. Among 693 subjects between the ages of 30 and 59 years, approx. 3% of males and 1% of females had Q-wave changes, and 16% of females and 4% of males had ST-T changes. Among males with Q-wave abnormalities, hyperlipemia was more frequent. There was also increased frequency of hypertension in those with elevated lipids. The data indicate the occurrence of some hyperlipemia in this population which could be of the familial-combined type; the elevated plasma lipids may contribute to the increased frequency of coronary heart disease.

Effects of gene-environment interactions on cardiovascular risk factors in Chinese adolescent twins

A population-based sample of 73 male and 77 female monozygotic (MZ), and 41 male and 33 female dizygotic (DZ) Chinese adolescent twin pairs were studied to assess effects of gene-environment interactions of systolic blood pressure (SBP), diastolic blood pressure (DBP), serum cholesterol and triglyceride levels. Intrapair concordance in BP levels was found to be significantly associated with the interaction of zygosity and salty foods preference and also with that of zygosity and vegetable preference. A consistently positive and statistically significant association was observed between the intrapair difference in serum cholesterol and the interaction of zygosity and animal organ preference; while intrapair concordance in serum cholesterol was associated with the interaction of zygosity and milk consumption. Intrapair difference in serum triglycerides was associated with the interaction of zygosity and fish preference, and a significant association was also found between the intrapair concordance in serum triglycerides and the interaction of zygosity and sweets preference. These observations suggest that the impact of these environmental agents may be influenced by the genotype.

Prevention of age-associated loss of autonomy: epidemiological approaches

The concept of autonomy is proposed as a global objective of health and social services and epidemiological contributions to devising procedures for maintaining autonomy of old people are reviewed. It is suggested that the conventional model of "normal" vs "pathological" aging, identification of the "elderly" as a separate adult age group and preoccupation with clinical as opposed to public health models of intervention and with service provision rather than with clients' needs are less than optimal. More attention should also be given to the identification of extrinsic factors in aging and to recognising ways in which the effects of aging are aggravated by social conditions and unrelieved by ineffectual and inappropriate services. Epidemiology has more to contribute to meeting the challenges of aging than is generally recognised.

Hypothesis: discrepancy between intra- and interpopulation studies of the relationship between dietary salt and blood pressure: fact or fiction?

It is a paradox that intra-population studies fail to show significant correlation between sodium excretion and blood pressure while a clear relationship exists in cross-cultural studies. Since daily variation of sodium excretion is high, the discrepancy between the two observations could be due to non-comparable data on sodium excretion. This is a discussion of the hypothesis that the finding of a significant correlation or not between sodium excretion and blood pressure depends on the statistical analysis of the data.

Environmental effects on cardiovascular risk factors in Chinese adolescent monozygotic twins

The monozygotic (MZ) cotwin control method was employed to elucidate possible environmental determinants of systolic blood pressure (SBP), diastolic blood pressure (DBP), serum cholesterol and triglyceride levels. A population-based twin sample of 73 male and 77 females MZ twin pairs was recruited from 12 junior high schools in Taipei city. Intrapair differences in blood pressure were negatively associated with intrapair difference in vegetable preference, attaining significance for DBP in males and SBP in females. Cholesterol was positively associated with milk consumption and preference for sweets, fried foods, meat and fish. A negative association was also observed between cholesterol and vegetable preference. These associations for cholesterol were significant in males only. Triglyceride level negatively associated with preferences for sweets and vegetable, attaining significance for vegetables in both males and females and for sweets in males only.

Blood pressure response to dietary sodium restriction in normotensive adults

Sixteen healthy, normotensive husband-wife pairs participated in a study to investigate the effect of reduction of dietary sodium intake (goal less than or equal to 60 mEq/day) on blood pressure. Sodium excretion decreased from a control average of 152.7 +/- 10.1 (SE) mEq/day to 69.5 +/- 4.5 mEq/day (p less than 0.001). Results indicated significant decreases in both systolic (p less than 0.001) and diastolic (p less than 0.001) blood pressure after a period of sodium restriction. In the entire group, there was no significant change in potassium excretion (58.4 +/- 3.2 vs 54.6 +/- 3.5 mEq/day) or body weight (76.0 +/- 2.8 vs 75.3 +/- 2.7 kg). Although there was variability in the blood pressure response, the decrease in blood pressure was significantly correlated with the magnitude of sodium restriction (r = 0.36, p less than 0.03). These results indicate that the blood pressure response to sodium restriction may not be limited to individuals with hypertension and that the response is heterogeneous in normotensive subjects.

Genetic and sociocultural components of high blood pressure

The cardiovascular diseases exert widely differing contributions to the total burden of mortality and morbidity in extant human populations. To a large extent these differences are a reflection of the variable distribution of specific antecedent risk factors. For one such risk factor, blood pressure, there is considerable variability in its distribution between different ethnic groups, especially between traditional and nontraditional societies. Intensive epidemiological studies in Western societies, together with a number of cross-cultural comparisons, suggest that the major determinants of high blood pressure are likely to be a constellation of sociocultural factors, with genetic determination being limited to the interaction between genotype and environment. Studies of populations in sociocultural transition offer an unique opportunity to identify the relative influence of specific sociocultural factors on the rate of change of blood pressure. In addition, when the study of such populations is placed in a quasi-experimental context, genetic-environmental interactions may also be detected. This strategy is illustrated by a study of the changing blood pressure distribution in Tokelauan migrants. Such an approach requires the initial definition of a response variable which measures change in blood pressure as a consequence of migration. The response variable, which identifies the relative influence of concomitants such as weight, age, and obesity, can then be subjected to genetic analysis. In the Tokelau case, blood pressure response tends to be positive in migrants but negative in nonmigrants. Further statistical analysis indicates that there is a small proportion of high responders in both populations and that these cluster in families in the migrant population. However, estimates of the transmission parameter suggest that sociocultural transmission, rather than Mendelian segregation, is responsible. To date there is little evidence that genetic-environmental interactions have had any impact on the development of hypertension in this migrant population.

Relation of blood pressure to reported intake of salt, saturated fats, and alcohol in healthy middle-aged population

The association of blood pressure with reported intake of salt, saturated fats, and alcohol was studied in a sample of 8479 subjects based on a cross sectional survey in a population aged 30 to 64 years. A consistent association was found between the mean arterial pressure and the intake of alcohol (p less than 0.001) and saturated fats (p less than 0.01). There was also a weak association between blood pressure and dietary salt intake, but this association was mostly explained by the correlation of salt intake with alcohol and saturated fats. The observed relationships support the hypothesis that blood pressure is influenced by diet.

Blood pressure, ethnic group, and salt intake in Belize

A total of 1316 individuals were studied in seven villages in Belize, Central America. This represented 92% of the area population aged over 18. Generally, they were members of three ethnic groups--Maya, Spanish, and Creole. The systolic and diastolic IV and V blood pressures were recorded using standardised procedure. Significant differences in blood pressure, weight, and obesity were found between ethnic groups in both sexes, Creoles having higher means than the other groups. Significant relationships with blood pressure were found with obesity, age, and number of children. An early morning urine specimen was obtained from a random 50% of the men, and only in Creoles was there an association between raised blood pressure and sodium/potassium urinary excretion ratio.

The effect of sodium intake on the blood pressure related to age and sex

Two hundred and one volunteers with no known hypertension and 60 patients with untreated hypertension were entered into a study that compared the effect of two levels of sodium intake on blood pressure. One hundred and fifty-four volunteers and 46 hypertensive patients reached compliance goals, with a urinary sodium excretion on the high sodium diet twice that on the reduced sodium intake. The blood pressure on the high sodium diet was 4.5 +/- 0.5 mmHg (n = 154 p less than 0.001) higher than on the reduced sodium diet in normotensive individuals and was increased by 8.4 +/- 1.5 mmHg (n = 46 p less than 0.001) in hypertensive individuals. In the volunteer group the major rise in blood pressure occurred in people over the age of 50. In the hypertensive patients the alteration in blood pressure was not age dependent. In the younger age groups some individuals had an increase in blood pressure when on the high sodium intake which was outside the spontaneous variations in blood pressure of a control group. This implied that a number of young normotensive individuals were susceptible to this alteration in sodium intake. Changes in sodium intake alter blood pressure in hypertensive people, in normotensive people over 50 and in a small number of younger normotensive people. Overall reduction of sodium intake from 200 - 70 mmol/day would reduce the blood pressure level of the population and would reduce the number of people who have a blood pressure that requires drug therapy.

Estimating dietary sodium intake in individuals receiving a randomly fluctuating intake

Previous investigations examining techniques to estimate sodium intake in free-living persons failed to consider a varying intake or were not conducted under circumstances in which the intake was actually known. To examine the utility of 24-hour and nocturnal urine collections as estimation of sodium intake under such conditions, we studied 43 white and black men and women ingesting a known sodium intake for 10 days that was randomly varied daily, with a mean intake of 150 mEq/day + 2 SD (range, 50 to 250 mEq/day). The mean 24-hour sodium excretion (UNaV) per day was and 24-hour UNaV estimated that day's sodium intake accurately for the entire 10 days, the average of several 24-hour collections was required. Nine collections were optimal (r = 0.75). Nocturnal specimens were not helpful; the average of all 10 collections correlated weakly (r = 0.30) with sodium intake. These data suggest that to estimate mean sodium intake accurately in free-living persons, only 24-hour collections are useful, although nocturnal collections are helpful in evaluating compliance with low sodium intake.