The association between blood pressure and the prevalence of hypertension with geographical latitude and solar radiation: results from the Chilean Health Survey 2009-2010 Short Title: Geographical latitude, solar radiation and blood pressure

Importance Hypertension is a major risk factor for cardiovascular disease. There are significant geographical differences in the prevalence of hypertension around the world. The reasons for this are not completely understood. Objective To explore the relationship between geographical latitude and solar radiation with blood pressure and hypertension prevalence. Setting Chilean general population. Participants Adult population of the Chilean Health Survey 2009-2010 (n=4,634). Exposures Solar radiation and geographical latitude. Main Outcome Values of systolic and diastolic blood pressure and presence of hypertension. Results The prevalence of hypertension was significantly higher in the South (37.4%) compared with the Central (34.0%) and North (29.3%) zones (P<.001). Systolic pressure was significantly higher in the South (126. 3 [Interquartile range (IQR) 113.7 – 143.0] mmHg) than Central (123.0 [IQR 112.7 – 139.0] mmHg) and North (121.0 [IQR 109.7 – 135.0] mmHg) zones (P<.001). The prevalence of hypertension was associated with latitude (Odds Ratio (OR), 1.014 [95% Confidence Intervals (CI) 1.007, 1.021] P<.001) and solar radiation (OR, 0.963 [95% CI 0.944, 0.982], P<.001). These associations persisted after adjustment for multiple variables (latitude OR, 1.012 [95% CI 1.002, 1.021], P=.02 and solar radiation OR, 0.973 [95% CI 0.949, 0.999], P=.04). Blood pressure was associated with latitude (systolic β coefficient 0.194 [95% CI 0.117, 0.271], P<.001 and diastolic β coefficient 0.080 [95% CI 0.043,0.118], P<.001) and solar radiation (systolic β coefficient -0.533 [95% CI -0.744, 0.322], P<.001 and diastolic β coefficient -0.197 [95% CI -0.301, -.094], P<.001). The association between systolic pressure and latitude (β coefficient 0.109 [95% CI 0.047, 0.172], 4 P=.001) and solar radiation (β coefficient -0.276[95% CI -0.448, -0.103], P=.002) persisted afer adjustment. However, after adjustment, the association between diastolic pressure and latitude (β coefficient 0.033 [95% CI -0.003, 0.070], P=.07) and solar radiation (β coefficient -0.067 [95% CI -0.167, 0.033], P=.19) was no longer significant. Conclusion and Relevance In the Chilean population the prevalence of hypertension and higher systolic pressure are associated with living further from the Equator and reduced exposure to solar radiation. Future work should investigate the potential mechanisms of this association as well as the potential impact on public health.