Difference In Salt Intake Research Articles

Dietary Sodium Intake and Arterial Blood Pressure

We sought to summarize major recent studies in the field of dietary sodium intake and arterial blood pressure, and discuss the following trials. INTERSALT: Sodium intake correlates with the rise in blood pressure with age, but not with the prevalence of hypertension. The population study identified a minimal impact of sodium intake on blood pressure (0.9 mm Hg/10 mmol difference in salt intake). DASH: This diet induced significant reductions in blood pressure compared with the control diet. Further decreases were observed with DASH and a 50 mmol/day sodium intake. VANGUARD: Blood pressure was inversely related to urinary potassium, calcium and magnesium but not to sodium excretion. TONE: Cardiovascular events were highest in the usual care group (83%) and lowest in the sodium reduction-plus-weight loss group (56%). META-ANALYSIS: A systematic review of 11 long-term controlled randomized trials reported a small decrease (1.1 mm Hg) in median systolic but not diastolic blood pressure with a reduced dietary sodium intake. In conclusion, (1) sodium restriction in hypertensive patients reduces blood pressure, and (2) the long-term impact of reduced salt intake on blood pressure, mortality, and morbidity remains to be defined.

Correlation between left ventricular mass and urinary sodium excretion in specific genotypes of CYP11B2

Aldosterone has essential roles in regulating intravascular volume and blood pressure, and is suggested to influence cardiac structure. However, the association of polymorphisms in the aldosterone synthase gene (CYP11B2) with hypertension or cardiac hypertrophy remains controversial. To evaluate the distribution of polymorphisms in the CYP11B2 gene and the possible associations between genotypes and blood pressure, urinary excretion of aldosterone or electrolytes and echocardiographic measurements, in a Japanese population. We examined the association of two common diallelic polymorphisms within CYP11B2, one in the promoter -344T/C and the other an intron 2 gene conversion, with blood pressure, 24-h urinary excretion of aldosterone and electrolytes, and echocardiographic measurements, in a Japanese population. We confirmed significant linkage disequilibrium between these polymorphic loci and ethnic differences in frequency of the alleles. The -344C and -344T haplotypes apparently diverged before the intron conversion polymorphism was generated on the latter haplotype. Allele frequencies did not differ between 535 normotensive and 360 hypertensive individuals or between hypertensive individuals with higher and lower concentrations of renin. The only significant correlation was a positive correlation of left ventricular mass with 24-h urinary excretion of sodium, which occurred only in individuals with the -344CC genotype or the intron 2 conversion (-/-) genotype. The -344CC or intron 2 conversion (-/-) genotype in CYP11B2 may be a risk factor for developing sodium-sensitive cardiac hypertrophy. Ethnic differences in the distribution of CYP11B2 genotypes combined with differences in salt intake might account for inconsistencies between previous reports.

Treating the syndrome of inappropriate ADH secretion with isotonic saline.

It has been widely accepted that there is little use for saline treatment in the syndrome of inappropriate secretion of ADH (SIADH). However, having observed that most SIADH patients increased their plasma sodium (PNa) after 2 l isotonic saline over 24 h, we investigated whether urine osmolality or the sum of urinary sodium and potassium (UNa + K) predicted this response, in 17 consecutive patients with chronic SIADH. The initial measure of urinary sodium plus potassium (UNa + K t0) was weakly correlated to the change in PNa (DPNa) after infusion (r = -0.51; p < 0.05), while initial urine osmolality (UOSM t0) was a much better predictor (y = -0.024x + 12.90; r = -0.81; p < 0.001). The lack of predictive value for UNa + K t0 was probably because urine electrolyte concentrations were not maximal for the corresponding initial UOSM. This reflects differences in salt intake between the patients. The theoretical maximal value for UNa + K t0 (th max UNa + K t0) for a given USOM t0, was as good a predictor as UOSM t0 (th max UNa + K vs. DPNa: r = -0.81; p < 0.001). A theoretical model describing the effect of 2 l isotonic saline infusion on DPNa as a function of UNa + K, produced values comparable to those observed in our patients. Only 6/17 patients, those with UOSM > 530 mOsm/kg, had their hyponatraemia aggravated by 2 l isotonic saline. Many SIADH patients have lower UOSM; in most such patients, 2 l of isotonic saline will improve PNa.

Effect of a low salt diet on blood pressure and vasoactive hormones in the hereditary hypertriglyceridemic rat.

In hereditary HTG rats, basal systolic blood pressure using tail-cuff sphygmomanometry was significantly higher (122.1 +/- 2.1 mm Hg; n = 16) than that in NTG animals (107.1 +/- 1.52; n = 16). A low salt diet did not influence blood pressure in NTG rats during the consecutive 4 weekly periods. However, in the second week blood pressure in HTG rats rose significantly in both the control rats on a normal salt diet and those on a low salt diet (132.5 +/- 1.89, n = 8, and 132.6 +/- 1.93, n = 8). No further changes were registered in the third and fourth week in control HTG rats. On the other hand, blood pressure fell significantly in HTG rats on a low salt diet in the third week in comparison with the second week (119.5 +/- 3.2, n = 8), and it increased again in the fourth week (123.0 +/- 2.35, n = 8). Hormones in plasma were determined at the end of the experiment. Plasma levels of norepinephrine were not influenced by differences in salt intake and were significantly higher by about 45% in HTG than in NTG animals. The lowest concentration of corticosterone in plasma was found in control HTG rats (1.2 +/- 0.2 vs 4.6 +/- 0.8 micrograms/100 ml in control NTG rats). Nevertheless, corticosterone concentration increased in HTG rats on a low salt diet at comparable values found in NTG rats on a low salt diet (3.1 +/- 0.8 vs 4.3 +/- 1.5). Plasma renin activity and plasma aldosterone concentrations were not different in the NTG and HTG groups and were uninfluenced by the diets (Table 1). We conclude that the elevated blood pressure in HTG rats and its variations during the experiment may reflect more pronounced sympathetic activity in HTG rats rather than blood pressure dependency on different salt intake.

Effect of capsaicin neonatal treatment on the salt intake of the adult rat

The present study investigated the involvement of capsaicin-sensitive sensory neurons on salt intake control in the rat, following capsaicin neonatal treatment. Capsaicin did not affect salt appetite induced by intramuscular injection of deoxycorticosterone enantate, or by intracranial injection of renin. Moreover, it did not alter salt preference of rats given access to a variety of NaCl concentrations, or the need-free salt intake of multidepleted male rats. On the other hand, in response to furosemide-induced sodium depletion, the salt intake of capsaicin-treated rats was lower than that of controls. Howeverm, furosemide-induced Na + excretion of capsaicin-treated rats proved to be lower than that of controls, thus suggesting the difference in salt intake might be secondary to lower sensitivity of capsaicin-treated rats to the natriuretic action of furosemide. Salt intake is known to be influenced by sensory information from the oral cavity, from the liver and from the intravascular compartment. The absence of effect of capsaicin neonatal treatment suggests that sensory fibers relevant to salt intake control may not be capsaicin sensitive. On the other hand, our findings indicate that capsaicin treatment alters the renal response to furosemide and stimulate further studies on the effects of capsaicin on renal function.

Studies of Salt Intake in Hypertension

It has been suggested that small changes in population blood pressure will have a major impact upon the incidence of cardiovascular disease caused by blood pressure elevation. Early reports indicated a close correlation between intercultural differences in salt intake and blood pressure. Before such epidemiological associations can be translated into population advice, certain conditions have to be met. The association has to be validated scientifically, and persuasive evidence has to be produced that the relationship is causal and reversible by changes in salt intake. Further, risk-benefit analysis should indicate that net harm is unlikely. Finally it has to be demonstrated that the population measures being advocated will produce an adequate change in dietary salt intake. The small individual effects upon blood pressure being examined, and the prevailing changes in blood pressure and cardiovascular mortality suggest that data will always fall short of the ideal and therefore that extrapolation will always be necessary. Nevertheless, a review of the present evidence indicates the inadequacies of the available data as a basis for population advice.

Relationship between blood pressure and modernity among Ponapeans.

In the Micronesian island of Ponape blood pressures were found in 1947 and again in 1953 to be very low and to show no difference between age groups. As part of the US Trust Territory of the Pacific from 1945, the island had begun to change in the direction of modernity, the changes being most dramatic in the capital town of Kolonia, but no part of the island being unaffected. After a generation of modernization, a cross-sectional study was done to assess the impact of changing way of life on blood pressure. Communities were sampled at three levels of impact of modernization: the capital town of Kolonia, an intermediate area, and a remote area. No differences in salt intake were found for the three areas; but the population in the most modern area was younger and heavier. No consistent ecological differences were found in blood pressure level. Since there is considerable variation in modernity within each area, a Guttman-type scale of individual modernity was developed. No trends of variation of blood pressure with modernization were found to be consistent for both sexes and all areas. However, among males in the most modern area both systolic and diastolic pressures increased consistently with increasing modernity, controlling for age. For diastolic pressures, significant increases were found for all males, Kolonia males, and intermediate area males. When body mass as well as age were controlled, the strength of the trends decreased. But among Kolonia males the increase of diastolic pressure with increasing modernity remained highly significant; that of systolic pressure, marginally significant.