: No previous study addressed the relative contributions of environmental and genetic cues to the diurnal blood pressure rhythmicity. We firstly investigated the explained variance of environmental and clock genes in relation to the night-to-day ratio (NDR) and morning surge (MS), respectively.Design and method
: From 24-h ambulatory recordings of systolic blood pressure (SBP) obtained in untreated Chinese patients (51% women; mean age, 51 years), we computed NDR in 897 and MS in 637. Environmental cues included season, mean daily outdoor temperature, atmospheric pressure, humidity and weekday and the genetic cues variation in the clock genes BMAL1 (rs6486121), CRY2 (rs10838524) and CLOCK (rs1801260).Results
: SBP averaged (±SD) 126.7 ± 11.9 mmHg, NDR 0.86 ± 0.07 and MS 24.8 ± 10.7 mmHg. In adjusted analyses, NDR was 2.4% higher in summer and 1.8% lower in winter (P < 0.001) compared with the annual average with a small effect of temperature (P = 0.079); MS was 1.7 mmHg lower in summer and 1.1 mmHg higher in winter (P < 0.001). The other environmental cues did not add to NDR or MS variance (P ≥ 0.37). With adjustment for season and temperature, NDR was 3.30% (P = 0.017) higher in TT homozygotes (n = 27) compared with C allele carriers (n = 870) of BMAL1 rs6486121. In CLOCK rs1801260 C carriers (n = 83), MS was 3.7 mmHg (P = 0.003) higher than in TT homozygotes (n = 554). Of NDR and MS variance, season and temperature explained ∼8% and ∼3%, while for genetic cues these proportions were ∼1% or less.Conclusions:
In conclusion, environmental compared with genetic cues are substantially stronger drivers of the diurnal blood pressure rhythmicity probably because the former also change the expression of the proteins encoded in clock genes.