Diurnal urine sodium excretion and nighttime blood pressure: the timing dimension of salt consumption.

BACKGROUND: Blood pressure (BP) exhibits a well-established circadian rhythm under physiological conditions, with a nocturnal decline of approximately 10-20% relative to daytime levels (nocturnal dipping). Disruption of this pattern, manifested as nocturnal hypertension and/or impaired BP dipping, is common and strongly associated with adverse cardiovascular and renal outcomes in various populations. Apart from BP, renal sodium handling also follows a specific circadian pattern with predominant daytime excretion. SUMMARY: Increasing evidence indicates that disrupted diurnal urine sodium excretion, manifesting as impaired daytime and/or increased nighttime natriuresis, contributes to abnormal BP phenotypes, leading to elevated nighttime BP and impaired BP dipping. This review outlines the physiological mechanisms influencing diurnal sodium excretion and examines the pathophysiologic background of the relationship between disrupted diurnal sodium excretion and nighttime BP. In addition, it summarizes the evidence deriving from clinical studies in various populations that evaluate the associations of daytime and nighttime urine sodium excretion with BP and especially nighttime BP and discusses their implications for everyday practice. KEY MESSAGES: Disrupted diurnal sodium excretion is closely associated with nocturnal hypertension and impaired BP dipping. Nighttime BP is a strong predictor of cardiovascular and renal risk and should be routinely assessed. Combined evaluation of ambulatory BP and timed urine sodium excretion may improve risk stratification and guide individualized management strategies.