Seasonal variation in blood pressure and its relationship with outdoor temperature in 10 diverse regions of China:  the China Kadoorie Biobank.
OBJECTIVE
Mean blood pressure varies moderately with outdoor air temperature in many western populations. Substantial uncertainty exists, however, about the strength of the relationship in other populations and its relevance to age, adiposity, medical treatment, climate and housing conditions.


METHODS
To investigate the relationship of blood pressure with season and outdoor temperature, we analysed cross-sectional data from the China Kadoorie Biobank study of 506,673 adults aged 30-79 years recruited from 10 diverse urban and rural regions in China. Analyses related mean blood pressure - overall and in various subgroups - to mean local outdoor temperature.


RESULTS
The mean difference in SBP between summer (June-August) and winter (December-February) was 10 mmHg overall, and was more extreme, on average, in rural than in urban areas (12 vs. 8 mmHg; P for interaction <0.0001). Above 5°C, SBP was strongly inversely associated with outdoor temperature in all 10 areas studied, with 5.7 (SE 0.04) mmHg higher SBP per 10°C lower outdoor temperature. The association was stronger in older people and in those with lower BMI. At lower temperatures, there was no evidence of an association among participants who reported having central heating in their homes.


CONCLUSIONS
Blood pressure was strongly inversely associated with outdoor temperature in Chinese adults across a range of climatic conditions, although access to home central heating appeared to remove much of the association during the winter months. Seasonal variation in blood pressure should be considered in the clinical management of hypertension.
Clinical Trial Service Unit and Epidemiological Studies Unit, University of Oxford, UK. sarah.lewington@ctsu.ox.ac.uk
Sarah
S
Lewington
Liming
L
Li
Paul
P
Sherliker
Yu
Y
Guo
Iona
I
Millwood
Zheng
Z
Bian
Gary
G
Whitlock
Ling
L
Yang
Rory
R
Collins
Junshi
J
Chen
Xianping
X
Wu
Shaojie
S
Wang
Yihe
Y
Hu
Li
L
Jiang
Liqiu
L
Yang
Ben
B
Lacey
Richard
R
Peto
Zhengming
Z
Chen
D001794:Blood Pressure; D002681:China; D002980:Climate; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012621:Seasons; D013696:Temperature