Sodium intake and blood pressure in two Polynesian populations

Mechanisms of sodium-mediated injury in cardiovascular disease: old play, new scripts

There is a strong association between salt intake and cardiovascular diseases, particularly hypertension, on the population level. The mechanisms that explain this association remain incompletely understood and appear to extend beyond blood pressure. In this review, we describe some of the 'novel' roles of Na⁺ in cardiovascular health and disease: energetic implications of sodium handling in the kidneys; local accumulation in tissue; fluid dynamics; and the role of the microvasculature, with particular focus on the lymphatic system. We describe the interplay between these factors that involves body composition, metabolic signatures, inflammation and composition of the extracellular and intracellular milieus.

Hypertension in a mountainous province of Vietnam: prevalence and risk factors

Background

Hypertension (HTN) significantly contributes to global disease burden, and its prevalence varies amongst different countries and regions. This work is aimed to characterize the hypertensive prevalence and identify risk factors for HTN among the residents in five locations (four communes and one town) of Moc Chau district (Son La province, Vietnam).

Methods

A cross-sectional study with a cross-sectional methodology was done in selected places from August 2018 to December 2018. We interviewed 197 participants aged equal to or more than 18 years old and measured their blood pressure (BP). Univariate and multivariate logistic regression were applied.

Results

The overall HTN prevalence of 30.0% was recorded. The differences of HTN prevalence rates were seen by several characters including age groups (p <0.001), accompanying disease (p <0.001) and alcohol drinking (p <0.05). Factors independently associated with hypertension were age (ORs: 3.1 [1.1–9.1]; 6.1 [1.7–22.3]), much salty consumption (OR: 2.6 [1.1–6.6]), alcohol use (OR: 3.1 [1.2–8.1]), HTN familial history (OR: 4.2 [1.3–13.3]) and at least one suffering disease (OR: 5.2 [2.1–12.7]).

Conclusions

Thus, this study highlighted the high overall HTN prevalence in the Vietnam Northwestern region. Significant differences of HTN rate were observed among several characteristics such as age groups, accompanying disease and alcohol drinking. Age group, much salty consumption, alcohol use, hypertension familial history and at least one suffering disease were risk factors for HTN in study group.

Continued increases in blood pressure over two decades in Samoa (1991-2013); around one-third of the increase explained by rising obesity levels

BACKGROUND

To analyse trends over the period 1991-2013 in systolic blood pressure (SBP), diastolic blood pressure (DBP) and the prevalence of hypertension in adults aged 25-64 years in Samoa; and to assess the contribution of rising obesity levels to period trends.

METHODS

Unit record data from seven population-based surveys (n = 10,881) conducted between 1991 and 2013 were included for analysis. Surveys were adjusted to the nearest previous census to improve national representativeness. Hypertension was defined as SBP ≥140 mmHg and/or DBP ≥90 mmHg and/or on medication for hypertension. Obesity was measured by body mass index (BMI). Poisson, linear and meta-regression were used to assess period trends.

RESULTS

Over 1991-2013 mean SBP and DBP (mmHg), and the prevalence of hypertension (%) increased in both sexes. Increases in hypertension were: from 18.3 to 33.9% (p < 0.001) in men (mean BP from 122/74 to 132/78); and from 14.3 to 26.4% (p < 0.001) in women (mean BP from 118/73 to 126/78). The estimate of the age-adjusted mean SBP and DBP over 1991-2013, and the relative risk for hypertension in 2013 compared to 1991, were attenuated after adjusting for BMI: by 22% (men) and 32% (women) for mean SBP; 37% (men) and 32% (women) for mean DBP; and 19% in both sexes for hypertension.

CONCLUSIONS

Significant increases have occurred in SBP/DBP and hypertension prevalence in both sexes in Samoa during 1991-2013, which would contribute significantly to premature mortality from cardiovascular disease. Obesity accounts for around one-third of the rising trend in blood pressure in the Samoan population. Strengthening of population control of hypertension through reduction in obesity and salt intake, and case detection and treatment through primary care, is required to reduce premature mortality from cardiovascular disease in Samoa.

High prevalence of hypertension and its selected risk factors among adult tribal population in Central India

A community based cross-sectional study was carried out to assess the prevalence of hypertension and associated risk factors like salt intake, 24-h urinary sodium excretion and body mass index (BMI) among tribal population of Mandla District, Central India. A total of 3090 individuals, from 1258 house hold drawn from 33 sampled villages and 12 urban wards were studied for blood pressure measurements and clinical examination, while 414 urine samples were collected for estimation of 24-h sodium excretion. Bivariate and multivariate logistic regression were used to assess the associations of BMI, urinary sodium output and other risk factors with hypertension. Across the sample, 28.2% of males and 23.6% of females had either stage-I or stage-II hypertension. More than 8% of subjects <30 years were hypertensive. The prevalence of hypertension shows a strong association with the increase in BMI and tribals with BMI > 25 were considerably more to have high blood pressure. Salt intake is directly related to the hypertension. The prevalence of hypertension was significantly greater among those whose salt intake was more than 10 g per day. A positive association between urine sodium excretion and blood pressure was observed. The results of the present study show that the tribal population is also affected by the life style diseases at par with the non-tribal population.

Human genome evolution and development of cardiovascular risk factors through natural selection

Impressive advances in molecular genetic techniques allow to analyze the effects of natural selection on the development of human genome. For example, the trend towards blonde hair and blue eyes was documented. The approach to analyze possible effects of natural selection on the evolution of recent phenotypes with high risk of cardiovascular disease has not been described yet. A possible effect on the evolution of two main risk factors - hypercholesterolemia and hypertension - is presented. The close relationship of non-HDL cholesterol blood concentration to the proportion of pro-inflammatory macrophages in human visceral adipose tissue might be a result of long-lasting natural selection. Individuals with higher proportion of this phenotype might also display a higher ability to fight infection, which was very common in human setting from prehistory until Middle Ages. Successful battle against infections increased the probability to survive till reproductive age. Similar hypothesis was proposed to explain frequent hypertension in African Americans. A long-lasting selection for higher ability to conserve sodium during long-term adaptation to low sodium intake and hot weather was followed by a short-term (but very hard) natural selection of individuals during transatlantic slave transport. Only those with very high capability to retain sodium were able to survive. Natural selection of phenotypes with high plasma cholesterol concentration and/or high blood pressure is recently potentiated by high-fat high-sodium diet and overnutrition. This hypothesis is also supported by the advantage of familial hypercholesterolemia in the 19th century (at the time of high infection disease mortality) in contrast to the disadvantage of familial hypercholesterolemia during the actual period of high cardiovascular disease mortality.

Continued increases in hypertension over three decades in Fiji, and the influence of obesity

Objectives:

To analyse trends during 1980–2011 in hypertension prevalence and SBP/DBP by sex in Fiji Melanesian (i-Taukei) and Indian adults aged 25–64 years; and to assess effects of BMI.

Methods:

Unit record data from five population-based surveys were included (n = 14 191). Surveys were adjusted to the nearest previous census to improve national representativeness. Hypertension was defined as SBP at least 140 mmHg and/or DBP at least 90 mmHg and/or on medication for hypertension. Regression (Poisson and linear) was used to assess period trends.

Results:

Over 1980–2011 hypertension prevalence (%) and mean blood pressure (BP) (SBP/DBP mmHg) increased significantly (P < 0.001) in both sexes and ethnicities. Increases in hypertension were: from 16.2 to 41.3% in i-Taukei men (mean BP from 122/73 to 135/81); from 20.5 to 37.8% in Indian men (mean BP from 122/74 to 133/81); from 25.9 to 36.9% in i-Taukei women (mean BP from 126/76 to 132/81); and from 17.6 to 33.1% in Indian women (mean BP 117/71 to 130/81). The age-adjusted trend in hypertension and mean BP (over 32 years) declined after adjusting for BMI, with effects of obesity greater in women than men, and in Indians than i-Taukei. BMI explained 45% of the age-adjusted increase in DBP over the period in Indians (both sexes), and 16% (men) and 38% (women) in i-Taukei.

Conclusion:

Significant increases have occurred in hypertension prevalence and SBP/DBP in both sexes and ethnicities of Fiji during 1980–2011 with no indication of decline, contributing to significant premature mortality from cardiovascular disease.

Alteration of the substrate specificity of l-amino acid ligase and selective synthesis of Met-Gly as a salt taste enhancer

Dipeptides have unique physiological functions. This study focused on the salt-taste-enhancing dipeptide Met-Gly. BL00235, an l-amino acid ligase from Bacillus licheniformis NBRC12200, synthesizes Met-Gly as a major product as well as Met-Met as a by-product. To alter the substrate specificity of BL00235 and synthesize Met-Gly selectively, we chose to alter Pro85 residue based on the BL00235 crystal structure. We predicted that Met might be not recognized as a C-terminal substrate by occupying the space around C-terminal substrate. Pro85 was replaced with Phe, Tyr, and Trp, which have bulky aromatic side chains, by site-directed mutagenesis. These mutants lost the capacity to synthesize Met-Met, during the synthesis of Met-Gly. Furthermore, they did not synthesize Met-Met, even when methionine was used as a substrate. These results show that the amino acid residue at position 85 has a key role in C-terminal substrate specificity.

Environmental origins of hypertension: phylogeny, ontogeny and epigenetics

Hypertension and renal parenchymal disease are intricately linked. Primary renal parenchymal disease can impact on sodium and volume regulation and lead to hypertension, while arterial hypertension can induce renal parenchymal injury and precipitate renal dysfunction. The examination for clues to the environmental origins of renal disease and hypertension necessitates an approach that integrates epidemiology, clinical medicine, developmental biology, environmental science and epigenetics, such that the manner in which genes and the environment interact can be better understood to pave the way for innovative management paradigms with regards to prevention, diagnosis and treatment. This review summarizes the extant literature and provides cogent arguments for the need to evaluate chronic adult onset disease models such as hypertension and renal disease from the modern perspective that takes into account prenatal exposures, the intrauterine environment and development, postnatal growth and transgenerational epigenetic modifications with their attendant future disease risk from the individual to the population level.

Proposed nomenclature for salt intake and for reductions in dietary salt

There is considerable confusion about what ranges of dietary salt(a) could be considered low, normal, or high and also what ranges of reduction in dietary salt are small or large. The World Hypertension League with other organizations involved in dietary salt reduction have proposed a standardized nomenclature based on normal ancestral levels of salt intake and also on ranges of reduction in salt intake in clinical and population interventions. Low daily salt (sodium) intake where harm due to deficiency would be expected to occur is recommended to remain undefined because of inadequate research but likely <0.25 g (100 mg), normal (physiological) intake <2.5 g (1000 mg), recommended intake <5.0 g (2000 mg), high ≥5.0 g (2000 mg), very high >10 to 15 g (4000-6000 mg), and extremely high >15 g (6000 mg). Reductions in daily salt (sodium) intake are recommended to be called small if <2.5 g (1000 mg), moderate if 2.5 to 5.0 g (1000-2000 mg) and large if >5.0 g (2000 mg). Use of this nomenclature is likely to result in less confusion about salt intake and interventions to reduce dietary sodium.

Association between sodium intake and change in uric acid, urine albumin excretion, and the risk of developing hypertension

BACKGROUND

A high-sodium diet has little short-term effect on blood pressure in nonhypertensive individuals but, for unclear reasons, is associated with hypertension if consumed long term. We hypothesized that a chronically high sodium intake would be associated with increases in biomarkers of endothelial dysfunction, specifically serum uric acid (SUA) and urine albumin excretion (UAE), and that high sodium intake would be associated with incident hypertension among those with higher SUA and UAE.

METHODS AND RESULTS

We prospectively analyzed the associations between sodium intake and the change in SUA (n=4062) and UAE (n=4146) among participants of the Prevention of Renal and Vascular End Stage Disease (PREVEND) study who were not taking antihypertensive medications. We also examined the association of sodium intake with the incidence of hypertension (n=5556) among nonhypertensive participants. After adjustment for confounders, each 1-g-higher sodium intake was associated with a 1.2-μmol/L increase in SUA (P=0.01) and a 4.6-mg/d increase in UAE (P<0.001). The relation between sodium intake and incident hypertension varied according to SUA and UAE. For each 1-g-higher sodium intake, the adjusted hazard ratio for developing hypertension was 0.98 (95% confidence interval, 0.89-1.08) among those in the lowest tertile of SUA and 1.09 (1.02-1.16) among those in the highest tertile. Corresponding hazard ratios were 0.99 (confidence interval, 0.93-1.06) among participants whose UAE was <10 mg/d and 1.18 (confidence interval, 1.07-1.29) among those whose UAE was >15 mg/d.

CONCLUSIONS

Over time, higher sodium intake is associated with increases in SUA and UAE. Among individuals with higher SUA and urine UAE, a higher sodium intake is an independent risk factor for developing hypertension.

Does stress induce salt intake?

Psychological stress is a common feature of modern day societies, and contributes to the global burden of disease. It was proposed by Henry over 20 years ago that the salt intake of a society reflects the level of stress, and that stress, through its effect on increasing salt intake, is an important factor in the development of hypertension. This review evaluates the evidence from animal and human studies to determine if stress does induce a salt appetite and increase salt consumption in human subjects. Findings from animal studies suggest that stress may drive salt intake, with evidence for a potential mechanism via the sympatho-adrenal medullary system and/or the hypothalamo-pituitary-adrenal axis. In contrast, in the few laboratory studies conducted in human subjects, none has found that acute stress affects salt intake. However, one study demonstrated that life stress (chronic stress) was associated with increased consumption of snack foods, which included, but not specifically, highly salty snacks. Studies investigating the influence of chronic stress on eating behaviours are required, including consumption of salty foods. From the available evidence, we can conclude that in free-living, Na-replete individuals, consuming Na in excess of physiological requirements, stress is unlikely to be a major contributor to salt intake.

Sex differences in pulse pressure trends with age are cross-cultural

Sex differences in systolic and diastolic blood pressure levels and trends with age have been consistently observed in both industrialized and unindustrialized populations. However, the impact of sex on pulse pressure, an index of vascular aging, in unindustrialized populations has not been addressed. The objective of this report was to characterize sex differences in aging trends of pulse pressure within unindustrialized populations. Using PubMed and Medline, we identified 60 articles with blood pressure data from unacculturated or partially acculturated populations. Data on 27 populations from 22 articles were included for analysis, on the basis of adequate description of study design and blood pressure measurement. Blood pressure means of adult age groups were modeled by linear and polynomial regression. The pulse pressure levels of women were lower than those of men in early adulthood and higher in older ages. Women had a steeper, steady increase in pulse pressure with age than men (P<0.001), whereas men had a stronger curvilinear upswing in pulse pressure with age (P=0.006). Partially acculturated populations had higher pulse pressures than unacculturated populations. Sex had a stronger effect on pulse pressure than acculturation. Pulse pressure trajectories of unindustrialized populations were slightly attenuated compared with those seen in National Health and Nutritional Examination Surveys III and IV of the US population. A sex effect on pulse pressure trends with age prevails across unacculturated and acculturated populations. Accordingly, the biological principles of arterial aging, as expressed in pulse pressure, are the same in all humans, regardless of demography.

The Role of Salt in Hypertension

There is considerable evidence that salt is an important cause of hypertension. Primitive societies who ingest little or no salt have no hypertension. Also when diets very low in salt such as the rice and fruit diet are given to hypertensive patients, the blood pressure often falls toward normal. Unfortunately, when diets only moderately low in sodium have been given only minor reductions in blood pressure occur. Salt-induced hypertension has been produced in both man and experimental animals. The basic cause of the hypertension is an inability of the kidney to excrete the increased salt. Hemodynamic changes then occur which raise the blood pressure and so excrete the excess salt by pressure diuresis. The ability to excrete salt at normal levels of blood pressure varies from one individual to another. Those who require a higher than normal blood pressure are said to be "salt-sensitive". Those who can excrete excess salt at normal levels of blood pressure are called "salt resistant". The difference may be due to an inherited defect in the kidney to excrete salt. In any event, salt sensitive hypertension is effectively controlled with the administration of diuretics.

Single nucleotide polymorphism and lifestyle-related diseases in the Asia-Pacific region: comparative study in Okinawa, Palau and Thailand

Genetic differences between Asians and Caucasians may be involved in the rapid increase in lifestyle-related diseases in the Asia-Pacific region that has coincided with Westernisation of diets in the region. In the present study, we assessed correlation between 10 single nucleotide polymorphisms (SNPs) and chronic disease risk factors in age-matched and population-based groups in four Asian-Pacific locations: Okinawa, Palau and Thailand (two areas). The following allelic SNP profiles significantly differed (p<0.01) among the four populations, in both men and women: uncoupling protein 2 (UCP2), uncoupling protein 3 promoter (UCP3p), leptin receptor (LEPR) exon 6, and angiotensinogen (AGTa-20c). Multiple regression analyses showed significant associations between SNPs and clinical data. For men, these associations were between beta3 adrenergic receptor (beta3AR) and diastolic blood pressure (DBP) (p<0.01), UCP3p and total cholesterol (p<0.01), UCP2 and age (p<0.05), and AGTa-20c and age (p<0.01). For women, these associations were between LEPR exon 14 and body mass index (BMI) (p<0.05), UCP2 and systolic blood pressure (p<0.05), UCP3p and DBP (p<0.05), UCP2 and DBP (p<0.01), apolipoprotein E (ApoE)nd total cholesterol (p<0.01), beta3AR and triglyceride (p<0.05), AGTa-20c and triglyceride (p<0.05), and UCP2 and age (p<0.05). These results illustrate the interrelationships among SNPs and risk factors in the Asia-Pacific including China and Japan.

Acculturation to Western society as a risk factor for high blood pressure: a meta-analytic review

OBJECTIVE

A number of studies have documented that acculturation to western society is related to an increase in blood pressure (BP). Although there is evidence that higher socioeconomic status appears related to better cardiovascular health, increasing acculturation to western society appears related to worse cardiovascular health. The purpose of this meta-analysis was to investigate the association between acculturation and BP.

METHODS

Literature searches yielded 125 relevant research manuscripts, which were coded by teams of two independent raters. This study was conducted in 2003 and 2004, and research databases such as MEDLINE and PsychINFO were searched through 2004. Measures of association (effect sizes) were extracted for both systolic blood pressure (SBP) and diastolic blood pressure (DBP) readings. Random effects models were used to analyze the resulting data.

RESULTS

The overall effect sizes associated with acculturation were 0.28 for SBP and 0.30 for DBP, with increasing acculturation to western society related to higher BP. More acculturated individuals had an average of 4 mm Hg higher BP than less acculturated individuals, which is similar to the effect sizes of known risk factors for high BP such as diet and physical activity. The effects of acculturation on BP appear to be universal, with similar effect sizes found across all regions of the world. Change in BP due to acculturation was not related to body mass index (BMI) or cholesterol but was related to length of residence in the new culture, with the largest effect sizes seen on initial entry and then decreasing rapidly within the first few years. Sudden cultural changes, such as migration from rural to urban settings, resulted in the largest effect sizes, which finding supports the hypothesis that the stress of cultural change is important role in the acculturation effect.

CONCLUSIONS

Acculturation to western society is associated with higher BP, and the distress associated with cultural change appears to be more influential than changes in diet or physical activity. Future studies would benefit from investigating how cultural change affects health and examining whether some non-Western cultural values and practices are health protective.

Uric acid, evolution and primitive cultures

Hypertension is epidemic and currently affects 25% of the world's population and is a major cause of stroke, congestive heart failure, and end-stage renal disease. Interestingly, there is evidence that the increased frequency of hypertension is a recent event in human history and correlates with dietary changes associated with Westernization. In this article, we review the evidence that links uric acid to the cause and epidemiology of hypertension. Specifically, we review the evidence that the mutation of uricase that occurred in the Miocene that resulted in a higher serum uric acid in humans compared with most other mammals may have occurred as a means to increase blood pressure in early hominoids in response to a low-sodium and low-purine diet. We then review the evidence that the epidemic of hypertension that evolved with Westernization was associated with an increase in the intake of red meat with a marked increase in serum uric acid levels. Indeed, gout and hyperuricemia should be considered a part of the obesity, type 2 diabetes, and hypertension epidemic that is occurring worldwide. Although other mechanisms certainly contribute to the pathogenesis of hypertension, the possibility that serum uric acid level may have a major role is suggested by these studies.

Estimation of 24-h urinary sodium excretion using lean body mass and overnight urine collected by a pipe-sampling method

BACKGROUND Although salt intake can be estimated from 24-h urinary sodium excretion (Na24 ), for a long time there has been no precise and easy method for its measurement.

OBJECTIVE

To investigate the possibility of estimating Na24 using pipe-sampling of overnight urine and lean body mass.

PARTICIPANTS AND METHODS

Body height, body weight and body fat determined by bioelectrical impedance (lean body mass = body weight body fat) was measured in 351 healthy individuals (126 men, 225 women). Twenty-four-hour urine was collected and creatinine and sodium were measured. To predict 24-h urinary creatinine excretion (Cr24 ), the relationship between Cr24 and lean body mass was investigated. Both 24-h urine and overnight urine specimens were collected in 149 individuals (71 men, 78 women) using a sampling pipe (semi-automatic proportional urine sampling device; height 16 cm, width 1.5 cm). Multiple regression analysis was used to estimate Na24.

RESULTS

The prediction of Cr24 (Pr.UCr24 ) was derived from lean body mass. Using Pr.UCr24 and the overnight urinary Na/Cr excretion ratio (Na n /Cr n ), Na24 was estimated as 0.634 (Na n /Cr n ) Pr.UCr 24 + 104.7 mmol/day for men and 0.682 (Na n /Cr n ) Pr.UCr 24 + 62.6 mmol/day for women. The correlation coefficient (r) between true Na24 and Na24 estimated by these formulae was r = 0.78 ( P<0.001; mean difference SD-0.03 39.0 mmol/day).

CONCLUSIONS

A new pipe-sampling method using overnight urine and lean body mass was easy and reliable for the estimation of Na 24. Furthermore, this method is convenient and may enable counselling on salt intake.

Single nucleotide polymorphisms of thrifty genes for energy metabolism: evolutionary origins and prospects for intervention to prevent obesity-related diseases

The "thrifty" genotype and phenotype that save energy are detrimental to the health of people living in affluent societies. Individual differences in energy metabolism are caused primarily by single nucleotide polymorphisms (SNPs), some of which promote the development of obesity/type 2 diabetes mellitus. In this review, four major questions are addressed: (1) Why did regional differences in energy metabolism develop during evolution? (2) How do genes respond to starvation and affluence? (3) Which SNPs correspond to the hypothetical "thrifty genes"? (4) How can we cope with disease susceptibility caused by the "thrifty" SNPs? We examined mtDNA and genes for energy metabolism in people who live in several parts of Asia and the Pacific islands. We included 14 genes, and the SNP frequencies of PPAR gamma 2, LEPR, and UCP3-p and some other genes differ significantly between Mongoloids and Caucasoids. These differences in SNPs may have been caused by natural selection depending on the types of agriculture practiced in different regions. Interventions to counteract the adverse effects of "thrifty" SNPs have been partially effective.

Abnormal platelet function and calcium handling in Dahl salt-hypertensive rats

The effect of dietary salt on platelet function and Ca(2+) homeostasis was studied in Dahl (DS) rats, a genetic model of salt-sensitive hypertension. DS rats were fed a high-salt (DSHS) or a low-salt diet (DSLS) for up to 4 weeks, and the effects of salt loading on systolic blood pressure, platelet P-selectin expression, and platelet Ca(2+) homeostasis were measured. The high-salt diet increased blood pressure and markedly increased the amount of ionomycin (IM)-releasable Ca(2+) in platelet intracellular stores (Ca(2+)/IM). The alteration in Ca(2+) stores was not prevented when the hypertension was prevented by treatment with hydralazine and reserpine. The Ca(2+) store filling during platelet exposure to 1 mmol/L Ca(2+) for 5 minutes and the rate of sarcoplasmic/endoplasmic Ca(2+) ATPase-dependent Ca(45) uptake were higher in DSHS compared with that in DSLS. There was a decrease in thrombin-induced Ca(2+) influx in platelets from DSHS; consistent with this, agonist-induced P-selectin expression was decreased. In DSLS, nitric oxide accelerated reloading of platelet Ca(2+) stores after their emptying by thrombin but failed to do so in DSHS. These results indicate that in DS rats, a high-salt diet increases sarcoplasmic/endoplasmic Ca(2+) ATPase activity and the Ca(2+)/IM but decreases the reuptake of Ca(2+) caused by nitric oxide. Decreases in Ca(2+) influx and platelet P-selectin expression might be explained by changes in intracellular Ca(2+) stores in DSHS rats, which apparently is a heritable response to a high-salt diet.

Comparison of the mineral content of tap water and bottled waters

OBJECTIVES

Because of growing concern that constituents of drinking water may have adverse health effects, consumption of tap water in North America has decreased and consumption of bottled water has increased. Our objectives were to 1) determine whether North American tap water contains clinically important levels of calcium (Ca2+), magnesium (Mg2+), and sodium (Na+) and 2) determine whether differences in mineral content of tap water and commercially available bottled waters are clinically important.

DESIGN

We obtained mineral analysis reports from municipal water authorities of 21 major North American cities. Mineral content of tap water was compared with published data regarding commercially available bottled waters and with dietary reference intakes (DRIs).

MEASUREMENTS AND MAIN RESULTS

Mineral levels varied among tap water sources in North America and among bottled waters. European bottled waters generally contained higher mineral levels than North American tap water sources and North American bottled waters. For half of the tap water sources we examined, adults may fulfill between 8% and 16% of their Ca2+ DRI and between 6% and 31% of their Mg2+ DRI by drinking 2 liters per day. One liter of most moderate mineralization European bottled waters contained between 20% and 58% of the Ca2+ DRI and between 16% and 41% of the Mg2+ DRI in adults. High mineralization bottled waters often contained up to half of the maximum recommended daily intake of Na+.

CONCLUSION

Drinking water sources available to North Americans may contain high levels of Ca2+, Mg2+, and Na+ and may provide clinically important portions of the recommended dietary intake of these minerals. Physicians should encourage patients to check the mineral content of their drinking water, whether tap or bottled, and choose water most appropriate for their needs.

The diuretic chlorthalidone normalizes baroreceptor and Bezold-Jarisch reflexes in DOCA-salt hypertensive rats

The contributions of arterial baroreceptor and Bezold-Jarisch reflexes, and atrial natriuretic factor (ANF) to the anti-hypertensive effect of the diuretic chlorthalidone were investigated in rats with deoxycorticosterone acetate (DOCA)-salt-induced hypertension. Chlorthalidone (8 mg rat(-1)day(-1)added to food) was given to one group during all 20 days of DOCA (8 mg kg(-1)s.c. twice per week) administration (preventive regimen) and, to another group, 20 days after DOCA treatment was initiated until the 40th day (therapeutic regimen). DOCA caused a significant increase in mean arterial pressure, reduced arterial baroreflex, and increased both the Bezold-Jarisch reflex and pro-ANF converting enzyme activity. Chlorthalidone reversed or prevented the DOCA-salt-induced hypertension, which was accompanied by the normalization of both the arterial baroreflex and the Bezold-Jarisch reflex. Additionally, both preventive and therapeutic regimens with chlorthalidone did cause normalization of the plasma sodium concentration and pro-ANF converting enzyme activity in the left atrium that follows DOCA-salt hypertension. Although it is difficult to determine the relative importance of each of the above regulatory mechanisms altered by chlorthalidone treatment, these data indicate that they may account for the prevention or decrease of DOCA-salt-induced hypertension in rats.

Effect of dietary fiber and protein intake on blood pressure: a review of epidemiologic evidence

Observational epidemiologic studies identify an inverse relationship between dietary fiber and protein intake and blood pressure. This relationship has been demonstrated in both cross-sectional and prospective cohort studies and among various populations. Few randomized trials have examined the effect of dietary fiber and protein supplementation on blood pressure. In general, these intervention studies suggest that dietary fiber intake may lower blood pressure. However, they do not confirm the observational relationship between dietary protein and blood pressure. Furthermore, there are many limitations in the design of these clinical trials. Carefully designed randomized controlled trials with sufficient sample size to recognize a 2-3 mm Hg change in blood pressure using well-characterized dietary fiber and protein preparations are needed to confirm or refute these observed effects.

Variation in the mineral content of commercially available bottled waters: implications for health and disease

PURPOSE

Although the annual consumption of bottled water in North America is 12.7 gallons per capita, little is known about the potential health effects of these waters. We reviewed the amounts of major minerals found in commercially available bottled waters, the recommended daily allowances for these minerals, and their beneficial and harmful effects.

METHODS

We obtained the mineral content of various commercially available bottled waters in North America and Europe from The Pocket Guide to Bottled Water. We then conducted a Medline search to identify articles examining the beneficial and harmful effects of magnesium, sodium, and calcium.

RESULTS

Great variation exists in the mineral content of commercially available bottled waters. Among the bottled waters that we reviewed, the magnesium content ranges from 0 to 126 mg per liter, the sodium content ranges from 0 to 1,200 mg per liter, and the calcium content ranges from 0 to 546 mg per liter. Epidemiologic and clinical studies suggest that magnesium may reduce the frequency of sudden death, that sodium contributes to the occurrence of hypertension, and that calcium may help prevent osteoporosis.

CONCLUSION

The ideal bottled water should be rich in magnesium and calcium and have a low sodium content. Because there is great variation in the mineral content of commercially available bottled waters, the actual mineral content of bottled water should be considered when selecting one for consumption.

Effects of dietary salt and angiotensin-converting enzyme inhibitor on ATP-driven Ca pump and Na/Ca exchange in aortic rings of Dahl rats

We examined effects of dietary salt and cilazapril on ATP-driven Ca pump and Na/Ca exchange system in arterial smooth muscle of Dahl salt-sensitive (DS) rats. Twenty-four DS rats were assigned to 4 groups. H- and H+ rats were fed a high-salt diet. L- and L+ rats were fed a low-salt diet. H+ and L+ were administered cilazapril. Aortic rings were superfused with physiological saline, and isometric tension was measured. Relaxation rates of low-Na(+)-induced contractions were promoted by the removal of external Ca. Cilazapril significantly decreased blood pressure in both the high- and low-salt diet groups. Salt loading reduced relaxation rates in 1.2 mmol/l Na+, and enhanced the increase in relaxation rates from 1.2 mmol/l to normal Na+. A negative correlation was observed between Ca extrusion by the Ca pump and blood pressure, and a positive correlation was observed between Ca extrusion by Na/Ca exchange and blood pressure. The results suggest that the decrease of Ca2+ extrusion by the ATP-driven Ca pump resulting from a high-salt diet might lead to an elevation in the concentration of cellular Ca2+.

Sex differences in the response of blood pressure to modernization

Sex and age differences in the incidence of hypertension and blood pressure (BP) levels and their concomitants are examined among the Manus of Papua New Guinea in the context of modernization. For Manus men, BP increases directly with both degree of modernization and duration of migration to the local towns and larger cities of Papua New Guinea, accompanied by similar increases in body mass and subcutaneous fat. For Manus women, however, although body mass and fatness increase along the modernization continuum, BP does not. Risk for hypertension (140/90 mm Hg) was increased fourfold among men who resided in town (adjusted odds ratio [AOR] = 4.4, 95% confidence interval [CI] 1.5-13.2) and also among those who were in the highest tertile of fatness (AOR = 4.1, 95% CI 1.6-10.4). Among women, older age (≥45) alone significantly increased risk tenfold (AOR = 10.5, 95% CI 1.7-66.8). Using a Mantel-Haenszel χ² , a meta-analysis of sex and age differences in relative risk for hypertension (160/95 mm Hg) among 20 Pacific populations, 9 traditional living and 11 undergoing modernization, was performed. While young men showed increased risk in modernizing populations (summary relative risk [SRR] = 1.34, 95% CI 1.12-1.60), older men had significantly reduced risk for hypertension compared with women in both traditional (SRR = 0.46, 95% CI 0.33-0.64) and modernizing groups (SRR = 0.70, 95% CI 0.59-0.84). This crossover between the sexes with advancing age is also evident for BP levels in a larger sample of societies and suggests a biological basis for hypertension risk. © 1995 Wiley-Liss, Inc.

Adaptation, allometry, and hypertension

Essential hypertension is a "disease of civilization" but has a clear genetic component. From an evolutionary perspective, persistence in the human genome of elements capable of raising blood pressure presupposes their adaptive significance. Recently, two hypotheses that explicitly appeal to selectionist arguments, the "slavery" and "thrifty gene" theories, have been forwarded. We find neither completely successful, and we advance an alternative explanation of the adaptive importance of genes responsible for hypertension. We propose that blood pressure rises during childhood and adolescence to subserve homeostatic needs of the organism. Specifically, we contend that blood pressure is a flexible element in the repertoire of renal homeostatic mechanisms serving to match renal function to growth. The effect of modern diet and lifestyle on human growth stimulates earlier and more vigorous development, straining biologically necessary relationships between renal and general somatic growth and requiring compensation via homeostatic mechanisms preserved during evolution. Prime among such mechanisms is blood pressure, which rises as a compensation to maintain renal function in the face of greater growth. Since virtually all members of acculturated societies share in the modern lifestyle, the demands imposed by accelerated growth and development result in a populational shift to higher blood pressures, with a consequent increase in the prevalence of hypertension. We propose that hypertension is the product of maladaptation of highly genetically conserved mechanisms subserving important biological homeostatic needs. Elucidation of the mechanisms underlying hypertension will require approaches that examine the developmental processes linking growth to blood pressure.

Salt intake, blood pressure, and cardiovascular structure

Epidemiologic data revealed that a low sodium intake might have a favorable influence on blood pressure throughout an individual's lifetime. Sodium restriction was reported to lead to a modest fall in blood pressure in some studies, although a few groups of hypertensive patients experienced a rise in blood pressure. Left ventricular hypertrophy has been demonstrated to be related to cardiovascular morbidity and mortality independent of other risk factors. Dietary salt intake participates in the hypertrophic process independent of other determinants. Thus, 24-hour urinary sodium excretion has been reported to correlate with left ventricular mass independent of levels of arterial pressure. Three different mechanisms may link dietary salt intake to myocardial hypertrophy: the renin-angiotensin-aldosterone system, the sympathetic nervous system, and fluid volume homeostasis. Whether salt restriction reduces cardiovascular structural damage independent of arterial pressure has not been determined.

Salt sensitivity in hypertension. Renal and cardiovascular implications

The mechanisms responsible for the increase in blood pressure response to high salt intake in salt-sensitive patients with essential hypertension are complex and only partially understood. A complex interaction between neuroendocrine factors and the kidney may underlie the propensity for such patients to retain salt and develop salt-dependent hypertension. The possible role of vasodilator and natriuretic agents, such as the prostaglandins, endothelium-derived relaxing factor, atrial natriuretic factor, and kinin-kallikrein system, requires further investigation. An association between salt sensitivity and a greater propensity to develop renal failure has been described in certain groups of hypertensive patients, such as blacks, the elderly, and those with diabetes mellitus. Salt-sensitive patients with essential hypertension manifest a deranged renal hemodynamic adaptation to a high dietary salt intake. During a low salt diet, salt-sensitive and salt-resistant patients have similar mean arterial pressure, glomerular filtration rate, effective renal plasma flow, and filtration fraction. On the other hand, during a high salt intake glomerular filtration rate does not change in either group, and effective renal blood flow increases in salt-resistant but decreases in salt-sensitive patients; filtration fraction and glomerular capillary pressure decrease in salt-resistant but increase in salt-sensitive patients. Salt-sensitive patients are also more likely than salt-resistant patients to manifest left ventricular hypertrophy, microalbuminuria, and metabolic abnormalities that may predispose them to cardiovascular diseases. In conclusion, salt sensitivity in hypertension is associated with substantial renal, hemodynamic, and metabolic abnormalities that may enhance the risk of cardiovascular and renal morbidity.

Sodium and blood pressure: the puzzling results of intrapopulation epidemiologic studies

Most intrapopulation epidemiologic studies have been unable to find a significant association between sodium intake and blood pressure. The researchers have offered 2 opposing explanations: the hypothesis of the genetic susceptibility to sodium and the hypothesis of a weak association in general population. The evidence for and against each hypothesis is reviewed. The direction of future research is suggested.

The borderline hypertensive rat (BHR) as a model for environmentally-induced hypertension: a review and update

In recent years, the burgeoning disciplines of health psychology and behavioral medicine have renewed interest in the important role that environmental factors can play in the disease process. Nowhere is this concern more well-founded than in the area of cardiovascular disorders, particularly hypertension. Epidemiologists and clinicians have long suspected that stressful life events can be a sufficient trigger for the expression of hypertension in some individuals. To understand better the ways in which these variables interact in the disease process, researchers have tried, with limited success, to produce experimental hypertension in animals by exposing them to stressful environmental paradigms. Additionally, recent investigations using the borderline hypertensive rat (BHR) have demonstrated the important role genetic factors can play in mediating both the behavioral and cardiovascular responses to environmental stressors. The current paper will review these attempts and discuss recent data from experiments using a relatively new animal model that appears to be especially appropriate for the study of environmental-genetic factors in the elaboration of essential hypertension. We will also discuss potential mechanisms by which environmental stress influences arterial pressure and suggest avenues for further inquiry into the stress-disease relationship.

Biocultural predictors of age increases in adult blood pressure among Samoans

A five-year follow-up sample of 509 adult male and female Samoans experiencing modernization in American Samoa was studied to determine the relation between baseline biocultural factors and follow-up blood pressure level. Analyses were stratified by sex and baseline age: 18-44 and ≥45 years. Baseline factors in the predictive models included blood pressure level, sum of skinfolds, age, education level, and reported salt intake. This Samoan adult sample was characterized by high prevalence of overweight at all ages, continual fat gain, and high incidence of overweight in young adults over five years. Blood pressure levels were moderate in young adults considering the adiposity, although almost one-third of those ≥45 years of age were hypertensive. In young adults baseline adiposity was the most important predictor of follow-up blood pressure, whereas in older adults age itself was most important. As age increases, physiologic blood pressure regulation may become less labile due to long-term adiposity and salt intake and lead to persistent elevations of blood pressure.

Sodium depresses arterial baroreceptor reflex function in normotensive humans

Sodium may contribute to the pathogenesis of hypertension by impairing arterial baroreceptor reflex function. The objectives of this study were to 1) determine whether a high sodium diet depresses arterial baroreceptor reflex function in normotensive humans, and 2) determine whether alterations in baroreceptor reflex function are related to changes in arterial compliance. Seventeen normotensive men, aged 30 +/- 2 years, received 10 and 200 meq sodium per day diets, each for 5 days, in a randomized crossover trial. Carotid baroreceptor reflex function was assessed by measuring the blood pressure response to sequential neck suction (0, -10, -20, and -30 mm Hg) and neck pressure (0, +10, +20, and +30 mm Hg). Forearm vascular resistance was determined by venous occlusion plethysmography. Arterial compliance was evaluated by calculating the quotient of the diastolic blood pressure decay time constant and forearm vascular resistance. Blood pressure averaged 124 +/- 3/62 +/- 2 mm Hg on the low sodium diet and 122 +/- 3/60 +/- 2 mm Hg on the high sodium diet (p = NS). Baroreceptor reflex slopes representing the systolic and diastolic blood pressure responses to changes in neck chamber pressure were steeper in the subjects when randomly assigned to low sodium diet than to high sodium diet. Diastolic blood pressure decay time and forearm arterial compliance were similar during low and high sodium intake. We conclude that short-term exposure to a high sodium diet depresses carotid baroreceptor reflex function in normotensive humans. This observation cannot be attributed to changes in the arterial compliance.

Heterogeneity of the blood pressure distribution among Solomon Islands societies with increasing acculturation

This study illustrates the very complex nature of gene by environmental interactions influencing the blood pressure (BP) distribution in a series of genetically distinctive populations undergoing rapid acculturation. We report the results of two BP and anthropometric surveys on Solomon Islands societies separated by an interval of 14 to 19 years. While differences in acculturation existed at the time of the initial survey, the interval between surveys was marked by rapid acculturation in almost all societies. Seven of the eight societies originally covered were included in the resurvey, and a large but variable proportion of the original sample subjects was recovered in the follow-up. Because the genetic relationships of the societies have been described, we were able to establish the following points concerning the role of genetic differences in determining the distribution of BP among these populations and, more important, the interaction of these genetic differences with changes associated with increasing acculturation: 1) In the initial survey, mean adjusted systolic and diastolic BPs were significantly heterogeneous among societies within and among genetically related clusters of societies (genetic clusters) and sexes. At the same time, rank differences in these means were not associated with rank differences in acculturation status among societies ignoring cluster membership. 2) Importantly, in the follow-up survey increasing acculturation resulted in the disappearance of significant differences in mean systolic and diastolic BP among genetic clusters in males, despite continued significant heterogeneity among societies within genetic clusters. In females, differences among genetic clusters persisted, but the degree of significance was substantially less with increasing acculturation. We interpret these changes as evidence for genotype by environment interaction. 3) There were significant differences in interindividual variances of both systolic and diastolic BPs among genetic clusters in the first survey. Ranks of these variances were not significantly associated with acculturation rank. In the follow-up survey, however, most societies showed striking increases in the variance of both systolic and diastolic BPs with increased acculturation. These increases in variance of both systolic and diastolic BPs may be related to a) shifts in demography and/or anthropometry of some societies; b) increased range and intensity of environmental factors affecting BP and associated with increased acculturation; and/or c) genotype by environmental interactions. 4) The correlation between systolic and diastolic BP decreased over the interval for all societies within and among genetic clusters. This trend was partly the result of larger changes in variances for systolic than diastolic BP in the resurveys.(ABSTRACT TRUNCATED AT 400 WORDS)

Cellular mechanisms in hypertension and therapeutic implications in blacks

The high incidence and prevalence of hypertension in the black community in western societies led to early speculation that the black population consumed more sodium (sodium chloride) than the general population. However, numerous studies have failed to support this conclusion. It seems rather that it is the handling of sodium by the kidney (greater salt sensitivity) by many hypertensive blacks and the interaction of sodium with potassium, probably magnesium, calcium, and various transport systems at the cellular level that offer a better explanation of these observed phenomena.