Is the Metabolic Syndrome a Risk Factor for Nondipping Hypertensives?

There is much evidence that 24-h ambulatory blood pressure monitoring (ABPM) is superior to clinic blood pressure (BP) in the diagnostic and prognostic evaluation of hypertensive subjects, as it provides a large number of readings during daily life. In particular, ABPM provides the unique opportunity to evaluate BP variations at different times of the night, thus allowing the classification of hypertensive subjects as dippers and nondippers.1 Several studies have shown that a blunted fall in nocturnal BP may be of clinical relevance, as it is associated with more pronounced degrees of organ damage (OD) and with an increased risk of cardiovascular events. The metabolic syndrome (MS) is a phenotype which has been increasingly associated with a higher prevalence of subclinical alterations in a variety of organs, including left ventricular hypertrophy, carotid atherosclerosis, and renal dysfunction.2 This observation is clinically relevant because these markers of OD are related with an increased risk of cardiovascular disease. In the current issue of the American Journal of Hypertension, Hermida et al.3 reported the findings of a cross-sectional study aimed at investigating the relationship between the nondipping pattern (i.e., BP decrements at night ≤10% compared to average daytime values, assessed by two-consecutive 24-h ABPM) and the MS in a large cohort of nondiabetic, uncomplicated, untreated essential hypertensives. They found that: (i) the prevalence of the nondipping status was significantly greater in individuals with the MS as compared to those without it; (ii) the awake/asleep BP ratio, a quantitative index of the nocturnal BP fall, was inversely related with the number of the MS components, thus indicating that a stepwise decrease in night-time BP fall occurred with the increasing number of criteria for MS; (iii) among the MS components, waist circumference was the most significant correlate of the awake/asleep ratio. The interesting findings of this study are based on qualifying methodological aspects; first of all, dipper and nondipper hypertensives were identified by a 48 consecutive hours ABPM; this increases the likelihood that the degree of nocturnal BP fall represents a true clinical trait. Furthermore, patients on antihypertensive treatment, with concurrent type 2 diabetes and isolated clinic hypertension were excluded from the study, thus limiting the impact of potential confounders on BP circadian variations. Finally, monitoring of physical activity and body posture by actigraphy provided a reliable identification of daytime and night time periods and also documented that physical activity during asleep periods was lower among MS patients. From this perspective, this study adds a new piece of information on the mechanism(s) involved in the physiological BP changes between day and night (i.e., imbalance of the sympathetic-vagal regulation, structural vascular alterations, reduced sodium excretion during daytime)4,5 by showing that abdominal obesity and physical inactivity may have a role in the nondipping phenomenon. Accordingly, regular physical activity and sustained body weight loss may be beneficial, beyond their favorable metabolic and hemodynamic effects, in reducing the risk of nocturnal hypertension in MS subjects. The author declared no conflict of interest.