Blood pressure and nutrition in adults. The National Health and Nutrition Examination Survey

[Salt and blood pressure]

Current information on the relationship between sodium and blood-pressure regulation is reviewed from the point of view of epidemiological, clinical and experimental research, as well as evidence from intervention studies. Among other cations, calcium also has an influence on blood pressure. Epidemiological studies in particular are handicapped by the difficulties inherent in measuring salt intake in individuals with adequate accuracy. Despite remaining uncertainties and the need for further investigation, available data from different sources and a considerable number of studies justify the recommendation that the average daily salt intake of the population should not exceed 5 g (NaCl), corresponding to 85 meq or mmol of sodium (Na). This is a goal which should be approached gradually, paying simultaneous attention to other factors likely to be involved in the primary prevention of hypertension, especially overweight, and the maintenance of a sufficient supply of iodine and fluor for which salt is used as a vehicle in many countries.

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.

The relationships between alcoholic beverage use and other traits to blood pressure: a new Kaiser Permanente study

In a new study controlled for many factors, we reconfirmed the relationship of higher blood pressure to alcohol use. This relationship was slightly stronger in men, whites, and persons 55 years of age or older. A slight increase in blood pressure appeared in men who drank one to two drinks daily, and a continuous increase occurred at all higher drinking levels among white men who had constant drinking habits. Among women, an increase occurred only at three or more drinks daily. The data suggest complete regression, beginning within days, of alcohol-associated hypertension upon abstinence. Blood pressure showed minor differences with beverage preference: those who preferred liquor had higher adjusted mean blood pressure than those preferring wine or beer. The results of this study contribute to the likelihood that the alcohol-blood pressure association is causal. Smoking, coffee use, and tea use showed no association with higher blood pressure. Systolic pressure showed a positive relationship to total serum calcium and an inverse relationship to serum potassium, but diastolic pressure showed little relationship to these blood constituents; the explanations include a possible direct effect on regulation of blood pressure.

Factor analysis suggesting contrasting determinants for different blood pressure measurements

A multiple regression analysis was performed on statistically independent factors derived from blood pressure measurements and possible predictive variables in 618 Utah adults. Nine blood pressure factors obtained in a previous study composed the dependent variables; 35 anthropometric, questionnaire, and biochemical variables were reduced by factor analysis to 10 factors and used as independent variables. Body size and obesity had significant independent effects on different types of blood pressure: body size correlated most highly with systolic blood pressure, while obesity correlated most highly with sitting diastolic blood pressure measurements. Smoking did not correlate with sitting blood pressure but did show a significant positive correlation (after controlling for obesity) with tilt and supine diastolic pressure. Alcohol consumption correlated positively with sitting diastolic pressure when the effects of body size and obesity were controlled. No correlations were found between urinary potassium or sodium excretion and any blood pressure factors, but a significant positive correlation was seen between plasma sodium concentration and several different types of diastolic blood pressure measurements. Psychological stress showed a significant independent positive correlation with systolic blood pressure measurements that was strongest in adults over 35 years of age. The multiple correlation values for the multiple regression equations ranged from 0.19 to 0.52.

Inconsistencies in the correlates of blood pressure and heart rate

Various correlates of blood pressure (BP) and resting heart rate (HR) were compared in a study population of 1667 male and 520 female factory employees in Israel. The strong positive association between HR and both diastolic and systolic BP described in other epidemiologic studies was again evident. However, the correlates of HR and BP did not coincide. In multiple regression analyses age was found to be positively associated with BP in both sexes, whereas it was only moderately associated with HR in males and inversely associated with HR in females. Relative weight was positively associated with BP in both sexes but its association with HR was linear in young males and older females and U- or J-shaped in the other sub-groups. Cigarette smoking was inversely associated with diastolic BP in several subgroups but was positively associated with HR in most sub-groups. Ethnic-related variations in blood pressure, where found, did not parallel any differences in HR and in one group they were contradictory. The inconsistencies in the correlates of HR and blood pressure may reflect different mechanisms by which certain factors influence BP with varying effects on the HR.

Serum calcium fractions in essential hypertensive and matched normotensive subjects

Concentrations of serum total calcium and serum calcium fractions were compared between 28 hypertensive subjects and 28 race-sex-age-matched normotensive controls. Mean levels of serum total calcium were not different between the two groups. Hypertensive subjects had lower mean serum levels of ultrafilterable calcium (-0.32 mg/dl; p = 0.01), ionized calcium (-0.07 mg/dl; p = 0.09), and complexed calcium (-0.23 mg/dl; p = 0.04) and higher levels of protein-bound calcium (+0.36 mg/dl; p = 0.07). Estimated dietary calcium intake was similar in the two groups. These findings add to the evidence that essential hypertension is associated with perturbations in calcium metabolism.

Theoretical mechanisms of dietary calcium's antihypertensive action

Theoretical mechanisms underlying dietary calcium's antihypertensive action are reviewed. Based upon known defects in the regulation of membrane Ca2+ transport and regulation of intracellular free Ca2+ concentration, we conclude that maneuvers that favorably modify calcium homeostasis such as dietary calcium supplementation or 1,25 (OH)2 vitamin D3 administration appear to favorably modify these defects. Consequent improvements in vascular smooth muscle function may mediate the reductions in blood pressure that follows chronic dietary calcium supplementation in experimental hypertension and in the clinical setting.

Electrolyte intake and blood pressure: a study in contradictions and controversy

The widely accepted recommendation that hypertensive subjects benefit from a reduction of sodium intake has lately been challenged by a number of publications. From one analysis of the First National Health and Nutrition Examination Survey (NHANES) in the USA, the conclusion was reached that hypertension was associated more frequently with low nutritional sodium intake and low calcium intake. Other authors analysing the same data but using different criteria and statistical methods did not confirm such conclusions. The criticisms of epidemiological data concerning the relationship between salt intake and hypertension include frequently inconsistent definition of hypertension, failure to consider methodological uncertainties in the measurement of salt intake and excretion and inadequate control of confounding variables such as age, race, sex, body mass index and lifestyle. The claimed link between nutritional calcium and blood pressure is completely unclear and needs careful investigation. A reduction of sodium intake from the present day excessive amounts to moderate intakes of 3-6 g per day is still recommended in order to prevent the establishment of high blood pressure, to reduce hypertensive blood pressure levels or to reduce the doses of antihypertensive drugs. With mild hypertension being the main problem of high blood pressure management, further research is necessary to place dietary intervention in the non-pharmacological treatment of hypertension on a firmer, more rational footing.

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.

The relative contribution of body fat and fat pattern to blood pressure level

Although the association between body weight and blood pressure is irrefutable, body fat mass and blood pressure level may not necessarily be directly related. To clarify the relative contribution of fat mass to blood pressure level, we analyzed data on 399 adults consecutively entering a weight control program. Although most subjects were notably overweight (mean ideal body weight 177%), the population represented a wide spectrum of body weights and blood pressure levels. Study parameters included body fat mass (by total body water, 40K, and Steinkamp formula), lean body mass, body build (chest to height ratio), fat cell number and size from bilateral buttock biopsy specimens, upper fat pattern by arm to thigh circumference ratio, and central fat pattern by subscapular to triceps skinfold ratio. Our results concurred with previously noted correlations between obesity and blood pressure (as mean arterial pressure): weight (r = 0.44), percentage of body fat (r = 0.19), and absolute fat mass (r = 0.38; all p less than 0.01); however, lean body mass, age, and body build correlated highly with both fat mass and mean arterial pressure, thereby confounding this relationship. Multivariate analysis was performed to evaluate the relative contribution of fat mass to mean arterial pressure in the presence of these and other potentially confounding variables. Lean body mass, age, body build, and an upper body fat pattern were found to contribute significantly to the variation in mean arterial pressure (p less than 0.01). In their presence, percentage of body fat, absolute fat mass, central fat pattern, fat cell characteristics, and age of onset of obesity did not significantly improve the predictability of mean arterial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Diet, blood pressure, and multicollinearity

Recent reports of an inverse association between dietary calcium intake and hypertension stimulated this analysis of the relationship of blood pressure to more than 20 dietary factors among a group of 8000 Japanese men in Hawaii. Reported intakes of potassium, calcium, protein, and milk were all inversely associated with blood pressure levels when examined one at a time while controlling for other risk factors. Alcohol intake was directly associated with blood pressure, and was treated as a confounding variable in the analysis. The association of potassium intake with blood pressure was relatively stronger than the associations for other nutrients, but the intake of potassium was so highly correlated with intakes of calcium, milk, and protein that it was not statistically possible to identify the independent association of potassium and blood pressure. Calcium intake was strongly correlated with milk and potassium intakes, and only calcium from dairy sources was associated with blood pressure. These data thus indicate that several dietary factors are inversely related to blood pressure levels independently of other risk factors such as age, body mass, and alcohol intake. The high degree of intercorrelation (multicollinearity) among these dietary factors, however, indicates that the independent role of any specific nutrient cannot be conclusively separated from the possible effects of other nutrients in this type of study.

High blood pressure in older Americans. The First National Health and Nutrition Examination Survey

Data from a representative sample of the U.S. adult population obtained during 1971-1975 were analyzed to provide a profile of blood pressure (BP) levels and related nutritional and sociodemographic factors. Older adults (aged 55-74 years) had a twofold greater prevalence of high BP than younger adults (25-54 years), and older black persons had the highest rates. Isolated systolic elevation was uncommon under 54 years of age, but occurred in 5% to 10% of adults over 55 years and was less common than systolic-diastolic elevation. In older adults, body mass (weight/height2) had the strongest relationship to BP of all the nutritional variables. Alcohol consumption and dietary calcium and phosphorus were associated with high BP, but dietary sodium and salt use were not. The serum calcium/phosphorus ratio and serum urate were significantly higher in older adults with high BP. In general, the variables associated with elevated BP in older adults were similar to those in younger adults, although the strengths of the associations differed. Associations of factors useful for nonpharmacologic prevention and management of high BP in older persons were suggested from this survey.