Age-related changes in blood pressure twenty-four-hour pattern in normotensive subjects of two populations

OBJECTIVES: This study investigates the systolic (S) and diastolic (D) blood pressure (BP) 24-h pattern in normotensive healthy subjects belonging to two populations characterized respectively by a "non-salt culture" (Italian subjects) and a "salt culture" (Japanese subjects) in their dietary salt intake (4-6 g/day in Italians vs 10-12 g/day in Japanese). The comparison was performed by taking into consideration the within-day variability (WDV) and circadian rhythmicity (CR) of BP with respect to age. MATERIALS AND METHODS: Subjects investigated were 862 normotensive healthy subjects (308 Italians and 554 Japanese), stratified by age from 16 to 75 years, who volunteered for a noninvasive BP monitoring in an ordinary day of their life. The SBP and DBP time series were analyzed via conventional parametric statistics as well as chronobiological procedures. RESULTS: The biometric estimates demonstrate that BP changes in its WDV and CR as a function of age in both populations. Despite the difference in their habitual salt intake, the age-related changes in BP WDV and CR result to be almost comparable at the cross-sectional contrasts, giving origin to age-related trends for SBP and DBP which are significantly parallel. CONCLUSIONS: The comparability of BP WDV and CR in the two populations with a substantial difference in salt intake suggests that the normotensive status in human races is realized despite the difference in their habitual salt intake. This implies the ancestral development of mechanism(s) of adaptation to the possible "sodium luxus consumption". Although the adaptive mechanisms which provide a normotensive regimen under different conditions of sodium intake are almost unexplored, the racial adaptation to dietary salt constitutes, however, the initial condition for the cause-effect nexus between dietary salt intake and hypertension in human populations.