Journal of hypertension | 2021
Role of dietary sodium/potassium ratio in the blood pressure rise with age: novel evidence from the Coronary Artery Risk Development in Young Adults study.
Abstract
T he role of excess sodium intake on the blood pressure (BP) increase with age was highlighted by the international study of electrolyte excretion and blood pressure (INTERSALT) study investigators more than 30 years ago, through the cross-sectional findings of a landmark ecological study exploring the relationship between several lifestyle factors and BP [1]. Their graphical representation of the linear regression of the rate of BP increase with age on the average habitual sodium intake (estimated from 24h urinary sodium excretion) in 52 population samples from 32 countries has been mentioned and discussed inpossibly thousandsof publications and scientific meetings. Their results provided epidemiological support to the preexisting evidence of the importance of sodium intake for BP homeostasis deriving mainly from experimental animal and clinical studies.Yet, several objectionswere raised to the interpretation by the INTERSALT scientists of the observed statistical association as suggestive of a ‘causal’ relationship, generating a lively debate between supporters and detractors of the ‘salt hypothesis’ [2–6]. Among the studies in support of the INTERSALT findings, there was a very peculiar trial conducted a few years before. Two groups of newborn infants in Rotterdam had been randomly assigned to receive a formula diet with either regular or reduced salt content and had been followed for up to 6months: at this time, the group with higher salt intake showed a significantly higher SBP by 2.1 mmHg compared with the lower sodium group [7]. Fifteen years later, the group fed more salt during their first 6months of life was again found to have significantly higher SBP by 3.6 mmHg upon adjustment for possible confounders, in the absence of any other type of dietary intervention [8]. These data strongly suggested that the negative effects of high sodium intake on the arterial system start very early in life to become manifest through a gradual BP increase in the following years. Later on, both the trial of hypertension prevention Phase 1 study [9] and the dietary approaches to stop hypertension sodium trial [10] gave randomized clinical trial evidence of a ‘causal’ relation of sodium intake to BP, dealing however with individuals with high-normal BP, in whom a lower sodium intake was able to induce a decrease in BP compared with a control group on a higher salt intake. The article by Hisamatsu et al., in this issue of the Journal of Hypertension [11], provides novel evidence on the role of sodium intake on the BP increase with age and on the risk to develop clinically overt hypertension by initially ‘normotensive’ subjects. The study was part of the Coronary Artery Risk Development in Young Adults (CARDIA) investigation, a prospective observational survey that examined the trends and correlates of cardiovascular disease risk in young black and white men and women ages 18–30 years enrolled from 1985 to 1986 in four geographical areas in the United States [12]. Hisamatsu et al. analyzed the data from 1007 CARDIA participants (mean age, 30.2 years) who had their BP measured and provided at least two (most of them three) consecutive 24-h urine samples at baseline, and were reexamined at regular intervals in the subsequent 25 years. The authors concentrated not only on sodium but also on potassium intake by the study participants, classifying the study population in three groups by sex-specific medians of the average 24-h urinary electrolyte excretions: lower Na– higher K (about one-fifth of the population), higher Na– lower K (also about one-fifth), and all others. They found that SBP and DBP adjusted for age, BMI, alcohol intake and physical activity increased to a greater extent in the higher Na–lower K compared with the lower Na–higher K group, the difference achieving and maintaining statistical significance starting at 15 years and up to the final observation at 25 years from baseline. Although the concomitant antihypertensive drug treatment was a possible source of confounding in this study, Journal of Hypertension 2021, 39:000–000 Department of Clinical Medicine and Surgery, Federico II University Medical School, Naples, Italy