Background: Several studies have suggested that blacks, on average, have a blunted decline in nocturnal blood pressure (BP) as compared with nonblacks. It is unknown whether differences in traditional determinants of BP, specifically diet and obesity, account for observed differences in diurnal patterns.
Methods: We conducted an analysis of the Dietary Approaches to Stop Hypertension (DASH) trial that enrolled adults with prehypertension or stage 1 hypertension. At the end of a 3-week run-in period, ambulatory BP monitoring data were obtained on 333 participants, all of whom ate the same diet. Mean ambulatory daytime (6 am-11 pm) and nighttime (11 pm-6 am) systolic BP, diastolic BP, and heart rate (HR) were measured. Dipping was defined as a nighttime drop of less than 10% from mean daytime values.
Results: Office BP was similar in blacks and nonblacks, as were 24-hour and daytime BP and HR. However, blacks demonstrated a statistically significant, blunted nocturnal decline in BP and HR. Blacks were significantly more likely than nonblacks to have systolic nondipping (44.9% vs 26.7%, P = .001), diastolic nondipping (20.9% vs 11.6%, P = .03), and HR nondipping (40.9% vs 19.9%, P < .001). These differences persisted after adjustment for site, sex, age, body mass index, alcohol intake, physical activity, office BP (or HR), education, and income.
Conclusion: Blacks with similar office BP, and who consumed the same diet as nonblacks, had a blunted nocturnal decline in systolic BP, diastolic BP, and HR, even after factors that influence BP were controlled for.