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 and hypertension at the close of the millenium

"Can that which is unsavory be eaten without salt?" This question was directed at none other than God by Job, who also had other important problems to ponder. The question posed in this review is the notion that essential hypertension is induced and/or sustained by an unnecessarily high salt intake. If this is indeed the case, then a reduction of salt intake might prevent or effectively treat essential hypertension. A cross-sectional epidemiological study of salt intake in populations showed a positive association of sodium excretion with median blood pressure and the prevalence of hypertension; however, when four disparate populations were deleted, the associations disappeared. A Scottish report on a similarly large population minimized the importance of dietary sodium. A recently analysis of the National Health and Nutrition Examination Survey (NHANES) data base does not support the idea that lower salt intake improves all-cause or cardiovascular mortality; however, the analysis is not without weaknesses. Salt-sensitivity is based on the idea that some persons might be more susceptible to salt-induced effects on blood pressure than others. Indeed, several monogenic syndromes exhibit marked salt-sensitivity and their clarification has facilitated our understanding of basic mechanisms. Allelic variants of several genes may be important in salt-sensitive patients with essential hypertension. Meta-analyses of intervention trials in patients with essential hypertension show about a 5 mm Hg decrease in blood pressure with salt restriction. Among the normotensive, this decrease is less than 2 mm Hg. In terms of efficacy, salt restriction has not been shown superior to weight loss or a "vegetable" diet. Nonpharmacological approaches in hypertensive patients should be based on a comprehensive approach.     

Rapid growth problems: ascites and skeletal deformities in broilers

Over the last 40 yr, genetic selection for rapid growth and improved feed efficiency has been very effective in meat-type poultry. Combined with changes in the feed that have increased both the nutritional and physical density to encourage a high nutrient intake, growth rate has more than doubled. The effect of genetic selection for high muscle to bone ratio and high calorie intake of a ration that supplies all nutritional requirements causes significant mortality from cardiovascular disease. In the chicken, sudden death syndrome (flip-over) and pulmonary hypertension syndrome resulting in ascites are the most important. Ruptured aorta, spontaneous turkey cardiomyopathy (round heart), and cardiomyopathy causing sudden death produce high mortality in turkeys. Rapid growth induced by high nutrient intake alone can cause severe lameness, bone defects, and deformity, as these problems are seen in animals that have not been selected for rapid growth: dogs, horses, pigs, ratites and wild birds kept in zoologic gardens. In meat-type poultry, growth-related disease can be reduced or eliminated by reducing feed intake without affecting final body weight. Rapid growth alone may not be the pathogenic mechanism that results in cardiovascular or musculoskeletal defects. Metabolic imbalance induced by high nutrient intake may cause some of the conditions. These metabolic problems might be corrected without reducing growth rate.     

Mortality and light to moderate alcohol consumption after myocardial infarction

BACKGROUND: Although heavy alcohol consumption increases total mortality, light to moderate consumption decreases cardiovascular and all-cause mortality in apparently healthy people. Since data are sparse on the relation of light to moderate alcohol intake to mortality in patients with previous myocardial infarction, we did a prospective study of mortality in men. METHOD: Of 90,150 men in the Physicians' Health Study enrollment cohort who provided information on alcohol intake and who had no history of cancer, stroke, or liver disease, 5358 had a previous myocardial infarction. We estimated alcohol consumption by food-frequency questionnaire. FINDINGS: During a mean follow-up of 5 years, 920 men died. After adjustment for several potential confounders, moderate alcohol intake was associated with a significant decrease in total mortality (p=0.016). Compared with men who rarely or never drank alcohol, those who drank one to four drinks per month had a relative risk for total mortality of 0.85 (95% CI 0.69-1.05); for two to four drinks per week, the relative risk was 0.72 (0.58-0.89); for one drink per day 0.79 (0.64-9.96); and for two or more drinks per day 0.84 (0.55-1.26). INTERPRETATION: Men with previous myocardial infarction who consume small to moderate amounts of alcohol have a lower total mortality.     

Assessment of the salt-arterial pressure relationship in mild hypertensive subjects by 24-hour ambulatory monitoring

1. We have assessed the relationship between salt intake and 24 h ambulatory arterial pressure in middle aged men with essential hypertension. 2. During the run-in phase (1 month) we estimated the habitual sodium intake (the average Na excretion of two 24 h urine collections) of each participant (n = 14). In the randomized and crossover part of the study we contemplated a 'habitual' sodium intake phase, in which each individual received a fixed diet (about 30 mmol of Na+ and 65 mmol of K+) with additional salt so as to equalize the average intake of the run-in phase, as well as high sodium phases (habitual intake +50 and +100 mmol/day) and low sodium phases (habitual intake -50 and -100 mmol/day). After the trial, 10 patients underwent an additional week of fixed salt intake to assess the reproducibility of 24 h ambulatory monitoring. 3. Average 24 h arterial pressure at habitual sodium intake was significantly lower than that at high intake and significantly higher than at low sodium intake. Clinic arterial pressure showed similar trends but only systolic pressure changes at low sodium intake achieved statistical significance. 4. Analysis of the data on an individual basis showed a linear increase in 24 h mean arterial pressure with increasing levels of sodium intake in all but two cases (flat response in one case and a non-linear rise in the other case). The response pattern of clinic measurements was much less homogeneous. In the aggregate, there was a highly significant linear trend for ambulatory arterial pressure to rise with increasing levels of salt intake.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prior episodes of sodium depletion increase the need-free sodium intake of the rat.

Prior episodes of sodium depletion increase the daily 3% NaCl intake of rats. They ingest large volumes and continue to do so for as long as 3 months after recovery from sodium deficit while eating sodium-rich food and while plasma sodium concentration and renal function are normal. The increased daily intake of sodium is, therefore, need-free. There is a marked sex difference in the need-free intake of 3% NaCl. Female rats drink more salt than do male rats when they are sodium replete and depletion naive. Repeated depletions raise the need-free intakes of both sexes but the effect is greater in females. Plasma concentrations of angiotensin II and aldosterone, which are markedly elevated by each episode of sodium depletion, return to basal levels between and after depletions, and are not the cause of the chronically increased need-free salt intake of the multi-depleted rat. These results suggest that the persistent increase in daily 3% NaCl intake that occurs in the rat with a history of repeated sodium depletions is a permanent, nonpathological increase in avidity for the taste of salty substances that results in life-long overconsumption of salt. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex and sodium intake in the rat.

Female rats drink more 3% NaCl solution than do males, both when they need sodium (need-induced sodium intake or sodium appetite) and when they do not (need-free sodium intake). The sexual dimorphism of sodium intake is a secondary sexual characteristic because after castration at 1 day of age, male rats drank 3% NaCl in adulthood in a manner similar to that of females in both the need-free and need-induced state, and females given long-term neonatal testosterone drank low, malelike volumes of 3% NaCl on a daily need-free basis, but their response to sodium depletion was unchanged. This sexual dimorphism of sodium intake seems to be governed by testosterone that has been converted in the brain to estrogen because treatment of Day 1 castrated females with a nonaromatizable androgen, dihydrotestosterone, did not change either their need-free or their need-induced 3% NaCl intake. Castration in adulthood of male and female rats did not change their sodium consumption… (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estimates of interdialytic sodium and water intake based on the balance principle: differences between nondiabetic and diabetic subjects on hemodialysis

Whether salt or water intake is the primary cause of interdialytic weight gain (deltaW) has important implication for the design of measures to prevent large deltaW. In 17 hemodialysis patients dialyzed against a bath containing 140 mmol/L of sodium, monthly predialysis serum sodium was compared with post dialysis serum sodium. A decrease in serum sodium in the interdialytic period would indicate that primary water consumption accounts for at least part of the deltaW. Interdialytic sodium intake, isotonic fluid gain (deltaW(isotonic)) and net pure water gain (deltaWH2O) were calculated by balance formulae. Serum sodium concentration was corrected in diabetic subjects to the value corresponding to euglycemia (100 mg/dl). Estimated interdialytic sodium intake was compared with the prescribed sodium intake and, in seven subjects, to sodium intake estimated from dietary records. Results for nondiabetic subjects (N = 9): [Na]post 139.3 +/- 1.9 mmol/L, [Na]pre 140.1 +/- 2.1 mmol/L (NS), deltaW 1.15 +/- 0.55 L/24 hr, deltaW(isotonic) 1.33 +/- 0.57 L/24 hr, deltaWH2O -0.20 +/- 0.58 L/24 hr, estimated sodium intake 206 +/- 75 mmol/24 hr, prescribed sodium intake 121 +/- 29 mmol/24 hr (p = 0.028). Results for diabetic subjects (N = 7): [Na]post 140.1 +/- 2.5 mmol/L, [Na]pre 137.7 +/- 3.1 mmol/L (p < 0.01), deltaW 1.26 +/- 0.38 L/24 hr, deltaW(isotonic) 0.59 +/- 0.63 L/24 hr, deltaWH2O 0.66 +/- 0.39 L/24 hr, estimated sodium intake 160 +/- 81 mmol/24 hr, prescribed sodium intake 124 +/- 30 mmol/24 hr (NS), glycosylated hemoglobin 9.7 +/- 2.8% (normal, 4.1-5.7%). In seven subjects, estimates of sodium intake from balance formulae (233 +/- 113 mmol/24 hr) were not different from estimates from dietary records (212 +/- 87 mmol/24 hr). Sodium intake accounted for all the interdialytic weight gain in nondiabetic subjects. In diabetic patients, only approximately half of the interdialytic weight gain was accounted for by sodium intake. The other half was due to pure water gain, probably caused by hyperglycemia.     

Secondary prevention for ischemic heart disease. Relative numbers needed to treat with different therapies

Secondary prevention of ischemic heart disease refers to the process of preventing further morbidity and reducing mortality rates in patients with clinical manifestations of the disease. Twenty-five large randomized, clinical trials addressing mortality rates and cardiovascular morbidity in patients with established ischemic heart disease are reviewed. Broadly defined, these were trials of aspirin and antiplatelet agents, anticoagulants, beta-blockers, calcium channel blockers, angiotensin-converting enzyme inhibitors, lowering of cholesterol levels, exercise rehabilitation, and diet or vitamins. In trials using warfarin sodium, timolol maleate, propranolol hydrochloride, captopril, ramipril, and simvastatin and 2 diet studies, statistically significant improvements in total mortality rates were seen. Most other studies showed non-significant reductions in total mortality rates, with statistically significant reductions in 1 or more measures of cardiovascular morbidity. The methods necessary for the reader to calculate the number (of patients) needed to treat for other studies are also reviewed. The uses and limitations of the number needed to treat as a method to compare studies of different interventions in similar populations are discussed.     

Implications of the linear pressure-natriuresis relationship and importance of sodium sensitivity in hypertension

Although the concept of the pressure-natriuresis curve is very clear, considerable confusion concerning its importance and utility in understanding the pathophysiology of hypertension persists. We recently showed that the pressure-natriuresis curve could be considered linear. In this brief review, we would like to stress the advantages of treating it as a line. Its linear approximation simplifies understanding of the sodium sensitivity of the blood pressure and mechanisms of hypertension. The blood pressure can be expressed as the sum of two components: the non-sodium-sensitive component determined by the x intercept of the pressure-natriuresis curve and the sodium sensitive one determined by the product of the reciprocal of the slope and the amount of sodium intake. Theoretically, it can be affected in two different ways to cause hypertension; either a parallel shift along the blood pressure axis toward a higher blood pressure level due to the increase in the x intercept or a decrease in the slope. The parallel shift induces non-sodium-sensitive hypertension, whereas the decrease in slope induces sodium-sensitive hypertension. Thus, the linear approximation makes the definition of the sodium sensitivity of the blood pressure very clear and, furthermore, suggests that mechanisms of hypertension can be clarified if the determinants of the x intercept and the slope of the pressure-natriuresis curve are known. A clear definition of sodium sensitivity allows us to study its importance as a marker of a greater risk of renal and cardiovascular complications.     

Cardiovascular risk factors in relation to educational level in 36 000 men and women in The Netherlands

The study objective was to describe the associations between socioeconomic status and (concurrence of) cardiovascular risk factors. The Netherlands Monitoring Project on Cardiovascular Risk Factors is a screening project that was carried out from 1987-1991 in three cities. Cross-sectional data were obtained on educational level and on the prevalence of smoking, alcohol intake, physical inactivity, obesity, hypertension, hypercholesterolaemia and low HDL-cholesterol. A total of 36 000 men and women, aged 20-59 years participated. For all risk factors, except alcohol intake, a significant inverse association was found with educational level. Concurrence of risk factors was more prevalent in lower educated groups than in higher educated groups, but not more than can be expected under the condition of independence of the risk factors (no clustering). In conclusion, in the lower educated groups the prevalence of individual risk factors and of concurrence of risk factors was higher than in the higher educated groups. Concurrence of risk factors can have a synergistic effect on the risk for cardiovascular disease. Therefore socioeconomic differences in risk factors may explain a greater part of the socioeconomic differences in cardiovascular morbidity and mortality than is generally assumed.     

Nonpharmacologic approaches to hypertension. Weight, sodium, alcohol, exercise, and tobacco considerations

Weight loss decreases blood pressure, and this change can be sustained over the long-term when the lower weight is maintained. Salt restriction may be effective in blood pressure control only in salt-sensitive individuals. Heavy drinkers (those who drink more than three drinks [30 mL] daily) experience deleterious effects such as hypertension and more cardiovascular risk factors. Consequently, they should be advised to reduce alcohol intake to less than 30 mL daily. Endurance training with dynamic exercise appears to be beneficial for hypertensive patients, although recommendation guidelines are still imprecise. Finally, smoking cessation has not been proven to decrease blood pressure levels but should nonetheless be recommended because of its favorable effects on cardiovascular morbidity and mortality.     

The blunting of the antiproteinuric efficacy of ACE inhibition by high sodium intake can be restored by hydrochlorothiazide

BACKGROUND: Dietary sodium restriction enhances the antiproteinuric and blood pressure lowering effect of ACE inhibition. In clinical practice, however, long-term compliance to a low-sodium diet may be difficult to obtain. We therefore investigated whether the blunting of the antiproteinuric and blood pressure lowering efficacy of ACE inhibition by high sodium intake can be restored by the addition of a diuretic. PATIENTS AND METHODS: Seven proteinuric patients with non-diabetic renal disease on chronic ACE inhibition were studied during three consecutive 4-week periods: low sodium (50 mmol/day), high sodium (200 mmol/day) and high sodium plus hydrochlorothiazide (50 mg o.i.d.). RESULTS: During low sodium intake proteinuria was 3.1 (0.7-5.2) g/day, during high sodium intake proteinuria increased to 4.5 (1.6-9.2) g/day (P < 0.05). Interestingly, addition of hydrochlorothiazide again reduced proteinuria to 2.8 (0.6-5.8) g/day (P < 0.05). Mean arterial blood pressure was 89 (84-96), 98 (91-104) and 89 (83-94) mmHg (P < 0.05) during the three periods, respectively. CONCLUSION: Addition of hydrochlorothiazide can overcome the blunting of the therapeutic efficacy of ACE inhibition on proteinuria and blood pressure by a high sodium intake.     

Average intake of anti-oxidant (pro)vitamins and subsequent cancer mortality in the 16 cohorts of the Seven Countries Study

This ecologic study aimed to investigate whether differences in population mortality from lung, stomach and colorectal cancer among the 16 cohorts of the Seven Countries Study could be explained by differences in the average intake of anti-oxidant (pro)vitamins. In the 1960s, detailed dietary information was collected in small sub-samples of the cohorts by the dietary record method. In 1987, food-equivalent composites representing the average food intake of each cohort at baseline were collected locally and analyzed in a central laboratory. The vital status of all participants was verified after 25 years of follow-up. The average intake of vitamin C was strongly inversely related to the 25-year stomach-cancer mortality (r = -0.66, p = 0.01), also after adjustment for smoking and intake of salt or nitrate. The average intake of alpha-carotene, beta-carotene, and alpha-tocopherol were not independently related to mortality from lung, stomach or colorectal cancer, nor was vitamin C related to lung and colorectal cancer.     

Research notes: Sodium bicarbonate supplementation in diets for guinea fowl raised at high environmental temperatures

An experiment was designed to verify the effect of dietary NaHCO3 supplementation on performance of guinea fowl raised under high environmental temperatures (23.8 to 33.9 C) and average relative humidity of 78.7%. One hundred and forty guinea fowl in their final period of growth (56 to 84 d of age) were allotted to individual wire cages. Five isocaloric (3,000 kcal ME/kg) 16% CP diets based on corn and soybean meal and containing 0, 0.6, 1.2, 1.8, and 2.4% sodium bicarbonate were fed to the birds. The experiment followed a randomized block design with 28 birds per treatment (14 of each sex) with each bird being considered as one repetition. Results showed that weight gain, feed intake, feed conversion, mortality, blood pH, carcass yield, and carcass composition were not affected (P > 0.05) by dietary sodium bicarbonate supplementation. Weight gain, feed intake, feed conversion, carcass moisture, and fat content, however, were significantly (P < 0.05) affected by sex. Females showed 17.49% better weight gain, 7.16% greater feed intake, and 9.6% better feed conversion than males. These differences were exacerbated at supplementation levels of 1.2 and 1.8% sodium bicarbonate in the diet. Male birds showed carcass moisture values significantly (P < 0.05) greater than those of female birds; the opposite occurred with carcass fat levels. The use of sodium bicarbonate in levels up to 2.4% of the diet did not affect the performance of guinea fowl raised under the environmental conditions registered in this study.     

Dietary risk factors and their modification in cardiovascular disease.

This article provides an overview of dietary risk factors for cardiovascular disease and intervention strategies for their modification.The most prominent dietary risk factors for cardiovascular disease are hypertension, hypercholesterolemia, and obesity. Dietary fat and cholesterol contribute to hypercholesterolemia; diet sodium intake is linked to hypertension; and both conditions are exacerbated by obesity. Clinical strategies for modifying diet have relied heavily on education, skills training, and problem-solving procedures. Short-term changes in dietary behavior are often achieved, but maintenance remains an unresolved problem. Clinical approaches have been criticized as too limited in scope and too costly to deal with diet as a public health issue. A new generation of studies now underway is attempting to modify dietary behavior in entire populations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Epidemiology of hypertension in the elderly

DISTRIBUTION: Blood pressure tends to rise with increasing age. Six to eight per cent of people aged 60-69 years, and about 12-16% of those aged 70-79 years, are estimated to need treatment for raised systolic and diastolic blood pressures. DETERMINANTS: It seems likely that the rise in blood pressure with increasing age is partly explained by the determinants of blood pressure, such as sodium intake, body weight, physical exercise and alcohol consumption. MORTALITY: There is a linear relationship between the level of diastolic or systolic blood pressure and the risk of stroke or coronary heart disease. However, the relationship between blood pressure and mortality in later life may be obscured if concurrent illness lowers blood pressure; low blood pressure by itself may not be a risk factor for mortality. TREATMENT: Randomly allocated trials have consistently shown that the treatment of hypertension in men and women over 60 years of age reduces the incidence of stroke by about 40%, and some trials have also shown reductions in coronary events.     

Residential drug abuse treatment for probationers. Use of node-link mapping to enhance participation and progress

OBJECTIVES: the study was set up to explore regional disparities in France in the annual prevalence of cardiovascular risk factors (hypertension, high lipids, obesity, diabetes and tobacco consumption) and protective factors (alcohol intake) in members of the GAZEL Cohort and to determine which, if any, risk factors followed the same north-south gradient as the one known for cardiovascular mortality. METHODS: the population studied comprised 18,070 subjects aged from 35 to 50 years, employed by the French national gas and electricity company. Every year from 1989 to 1993 they received a self-administered questionnaire by mail. From the replies, differences in risk factor prevalence were evaluated by an odds ratio adjusted for sex and age, using a marginal model. RESULTS: a regional effect was found (p < 0.001) for arterial hypertension, with high odds ratios in northern France and low ratios in the south east, for high lipids, with high odds ratios in Champagne, the Loire region and Upper Normandy and low ratios in the south east and the Paris area, and for obesity, with high odds ratios in the north and north east and low ratios in the south, south east and west. CONCLUSION: these results show a gradient between the north and south east for hypertension, obesity, and to a lesser degree high lipids. This gradient corresponds to the known regional disparities for cardiovascular mortality.     

Salt intake in young children

Among adult Finns salt intake is about twice as high as the recommended levels and almost five-fold greater than the physiological requirement. Information as to salt intake in children has hitherto been sparse. Daily sodium intake among 1-5-year-olds was investigated in this study, and the foodstuffs from which it was derived were identified. In all age groups, sodium intake was at least two-fold greater than the Nordic recommendations, and among five-year-olds it exceeded the recommended intake for adults. Approximately half of the sodium intake was found to have derived from salt used in cooking. Levels of sodium derived by children from dairy, meat and grain products were also relatively high. Sodium intake in children after infancy merits greater attention than previously accorded it, as permanent eating habits and taste preferences are already formed at this age, and reasonable limits for salt intake should therefore be established during childhood.     

Calcium channel blockers, cancer incidence, and cancer mortality in a cohort of U.S. women: the nurses' health study

BACKGROUND: Some studies have suggested that the use of calcium channel blockers may increase the risk of cancer. A possible association of the use of calcium channel blockers with cancer incidence and cancer mortality was addressed using data from the Nurses' Health Study. METHODS: In this study, a total of 18,635 female nurses reported regularly taking at least 1 of 4 cardiovascular medications in 1988: diuretics, beta-blockers, calcium channel blockers, and/or angiotensin-converting enzyme (ACE) inhibitors. Cancer incidence and cancer deaths were ascertained until 1994. RESULTS: During 6 years of follow-up, 852 women were newly diagnosed with cancer and 335 women died of cancer. Women who reported the use of calcium channel blockers had no increased risk of newly diagnosed cancer compared with those taking other cardiovascular drugs (relative risk=1.02; 95% CI 0.83-1.26). The relative risk of dying from cancer associated with the self-reported use of calcium channel blockers was 1.25 (95% CI 0.91-1.72). Relative risks were adjusted for the following self-reported factors: age; weight; height; cholesterol level; systolic and diastolic blood pressure; smoking; alcohol intake; physical activity; menopausal status; postmenopausal hormone use; aspirin use; and history of diabetes, cancer, stroke, myocardial infarction, coronary artery bypass graft or percutaneous transluminal coronary angioplasty, angina, and hypertension. Regarding site specific cancer incidence and mortality, only lung cancer incidence was somewhat increased (RR=1.61; 95% CI 0.88-2.96). CONCLUSIONS: These data suggest no important increase in overall cancer incidence or cancer mortality related to the self-reported use of calcium channel blockers.