Abstract
Blunted day–night difference in blood pressure (BP) is an independent cardiovascular risk factor, although there is limited information on determinants of diurnal variation in BP. We investigated determinants of day–night difference in systolic (SBP) and diastolic (DBP) BP and how these compared with determinants of daytime and night-time SBP and DBP. We analysed the association of mean daytime, mean night-time and mean day–night difference (defined as (mean daytime−mean night-time)/mean daytime) in SBP and DBP with clinical, lifestyle and biochemical parameters from 1562 adult individuals (mean age 38.6) from 509 nuclear families recruited in the GRAPHIC Study. We estimated the heritability of the various BP phenotypes. In multivariate analysis, there were significant associations of age, sex, markers of adiposity (body mass index and waist–hip ratio), plasma lipids (total and low-density lipoprotein cholesterol and triglycerides), serum uric acid, alcohol intake and current smoking status on daytime or night-time SBP and/or DBP. Of these, only age (P=4.7 × 10−5), total cholesterol (P=0.002), plasma triglycerides (P=0.006) and current smoking (P=3.8 × 10−9) associated with day–night difference in SBP, and age (P=0.001), plasma triglyceride (P=2.2 × 10−5) and current smoking (3.8 × 10−4) associated with day–night difference in DBP. 24-h, daytime and night-time SBP and DBP showed substantial heritability (ranging from 18–43%). In contrast day–night difference in SBP showed a lower heritability (13%) while heritability of day–night difference in DBP was not significant. These data suggest that specific clinical, lifestyle and biochemical factors contribute to inter-individual variation in daytime, night-time and day–night differences in SBP and DBP. Variation in day–night differences in BP is largely non-genetic.
Highlights
Night-time blood pressure (BP) is typically lower than BP during the day
The distributions in night–day difference in systolic blood pressure (SBP) and diastolic blood pressure (DBP) calculated as a ratio of average night-time BP over average daytime BP are shown in Supplementary Figure 1
We examined whether the associations observed with day–night difference in SBP and DBP were influenced by mean day BPs, by adjusting for these variables
Summary
Night-time blood pressure (BP) is typically lower than BP during the day. Non-dipping of nocturnal BP and elevated nocturnal BP (nocturnal hypertension) have both emerged as independent risk factors for cardiovascular disease as well as cardiovascular and all-cause mortality.[1,2,3,4,5,6,7,8] the prognostic importance of non-dipping has been confirmed in multiple studies, especially since the advent of 24 h non-invasive ambulatory BP (ABP) monitoring, less information exists on determinants of diurnal variation in BP and whether these are similar to or differ from determinants of daytime and night-time BP.In this study, we have taken advantage of data, including ABPs, collected in the Genetic Regulation of Arterial Pressure in Humans in the Community (GRAPHIC) Study[9,10] to identify phenotypic characteristics associated with day–night difference in systolic (SBP) and diastolic (DBP) BPs and compare these with characteristics associated with mean daytime and nocturnal SBP and DBP in the same individuals. Night-time blood pressure (BP) is typically lower than BP during the day. Non-dipping of nocturnal BP and elevated nocturnal BP (nocturnal hypertension) have both emerged as independent risk factors for cardiovascular disease as well as cardiovascular and all-cause mortality.[1,2,3,4,5,6,7,8] the prognostic importance of non-dipping has been confirmed in multiple studies, especially since the advent of 24 h non-invasive ambulatory BP (ABP) monitoring, less information exists on determinants of diurnal variation in BP and whether these are similar to or differ from determinants of daytime and night-time BP. Because the GRAPHIC Study has a nuclear family design,[9,10] we were able to assess the extent of heritability of different time-related BP phenotypes in the same subjects and in particular assess the heritability of night–day differences in BP that has been studied less extensively
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