Epidemiological study of hypertension in natives of Spiti Valley in Himalayas and impact of hypobaric hypoxemia; a cross-sectional study.

Hypertension is the result of interaction between genetic vulnerability and exposure to unhealthy lifestyle. However, studies investigating the impact of cardiovascular adaptive response to hypobaric hypoxia and extreme cold in natives of high altitude on the development of hypertension have yielded conflicting results. A community based cross-sectional study was carried out in an unique population of Spiti valley of Greater Himalayas residing at an altitude of 3100-3500 m (group 1) and 3500 m and above (group 2) to evaluate the impact of altitude of residence on prevalence of hypertension. 413 subjects, age 20 years and above were selected by stratified cluster random sampling technique and screened for recording socio-demographic profile, anthropometrics, fasting blood sugar and blood pressure. There was no significant difference in the mean age (40.1 vs.38.0 years) and gender distribution (65.7% vs. 61.4% females) between the two groups. The overall prevalence of hypertension was 22.5% and achieved higher significance in group 1 (27.5%) compared to group 2 (19%); p < 0.041. The socioeconomic profile and lifestyle of group from higher altitude was significantly different with people being less educated, agriculture as main occupation compared to the group at lower altitude. On comparison, the same group had a lower prevalence of obesity 17.4% vs. 35.9% (p < 0.000), Diabetes 0.4% vs. 4.1% (p < 0.03) and impaired fasting glucose 5% vs. 11.1% (p < 0.06). Obesity, age and altitude of residence were significantly associated as independent predictors of prevalence of hypertension in this study. Hypobaric hypoxia thus appears to have a protective effect from developing hypertension. The prevalence of hypertension in natives of Spiti valley is thus influenced by lifestyle related risk factors, age and possibly altitude of residence.