Circadian variation of blood pressure in blacks: influence of age, gender and activity.

The purpose of the present study was to examine the circadian variation of blood pressure in black adults and determine the factors associated with this variation. Ambulatory blood pressure recordings were performed with a non-invasive recorder on 60 black subjects, 22 males and 38 females, with a mean age of 31 +/- 11 years and a mean causal blood pressure of 121/93 mm Hg. Only diastolic blood pressure exhibited a significant time of day effect (P less than 0.05). Age and gender were found to have both independent (r2 = 0.10 for each) and interactive effects (r2 = 0.26) on the level of systolic blood pressure during the day, but did not affect the diurnal pattern per se. Blood pressure at work (128/81 mm Hg) was higher (P less than 0.05) than blood pressure during miscellaneous activities (119/75 mm Hg) or sleep (119/73 mm Hg) but did not differ from blood pressure at home (123/77 mm Hg). Blood pressures at home while awake and during sleep were not different. These data show that blacks have a circadian rhythm of blood pressure which is characterized by a blunted nocturnal decline. In addition age, gender and activity are important determinants of the circadian variation. These results may help to explain racial differences in the prevalence of hypertension.