Investigating ethnic and sex-related differences of diurnal variation in 24-hour ambulatory blood pressure measurements

Introduction Blood pressure (BP) is dynamic, varying throughout the day in response to external and internal influences. Ambulatory BP monitoring (ABPM) is considered the gold standard measure and increased 24-hour BP variability is associated with CVD event risk and organ damage. Ethnic and sex differences in diurnal variation of BP have been described, such as the known blunted nocturnal dipping in small African ancestral populations. These studies were generally small in size and used simple measures, such as the difference between peak and lowest BP over a 24-hour period, but do not model the 24-hour diurnal rhythm in its entirety. Purpose To investigate diurnal rhythms of systolic blood pressure (SBP) and diastolic blood pressure (DBP) in Black African/Caribbean, South Asian, and White European males and females using ABPM data from a multiethnic cohort. Methods A cross-sectional analysis using data from the second wave of the Southall and Brent Revisited (SABRE) Study was conducted in 598 participants (221 European males, age (mean±SD): 69.9±6.1 years; 43 European females, age: 67.4±5.9; 206 South Asian males, age: 68.9±5.9 years; 29 South Asian females, age: 66.4±5.8; 58 African-Caribbean males, age: 69.69±5.4; 41 African-Caribbean females, age: 68.2±5.9). We used two-component cosinor models to identify mean circadian patterns of both males and females (separately) in each ethnicity using both fixed and random effects. We adjusted for age, body mass index (BMI), diabetes, and education. Results We found evidence of ethnic differences in the average level of SBP and DBP across 24-hours for females (p < 0.001), and a significant effect of ethnic differences in SBP in males (SBP: p = 0.006; DBP: p = 0.06). We also found ethnic differences in patterns of 24-hour diurnal rhythms for SBP and DBP in both sexes (males: SBP p < 0.001, DBP p < 0.001; females: SBP p = 0.001, DBP p =0.005). The mean predicted DBP of African-Caribbeans was higher, and SBP of Europeans lower, than that of other ethnic groups. The peak average SBP and DBP tended to occur later in the day for South Asians than other ethnicities. Conclusion Results indicate that diurnal rhythms of SBP and DBP differ by both sex and ethnicity. In future analyses, we will use these and other intensive longitudinal methods to relate ethnic and sex differences in ABPM to distal CVD endpoints. Future research comparing cosinor modelling to other modelling techniques would help clarify their relative merits in modeling ABPM and other intensely collected repeat measures.