Blood pressure variation among Tibetans at different altitudes

Abstract

Background: Age-related increase in blood pressure (BP) throughout adulthood have been commonly observed in industrialized and developing populations which is generally not observed in traditional populations. Based on studies in the Andes, Tien Shan, Pamir and US highlands, BP values are generally lower in high- than low-altitude populations. At present, Tibetans are residing at different altitudes in India and little is known about BP variation for this population.

Aims: This study reports BP variation among Tibetans in India in view of the hypothesis of age-related increase and of lower BP at high altitude.

Subjects and methods: BP, height, weight, triceps skinfold thickness (SFT), mid-upper arm circumference (MUAC), and haemoglobin and haematocrit level were obtained from 1091 individuals (508 males, 583 females) at four different settlements, one being at high altitude (Choglamsar, Leh; altitude: 3521 m) and three at low altitudes (Bylakuppe, Chandragiri and Delhi; altitude: less than 1000 m), which were pooled. Comparison between altitudes was carried out separately for the two sexes and for the two age groups: children and adolescents 10-19 years of age; and adults 20 years and above. Those independent variables that could significantly explain the variance in systolic blood pressure (SBP) and diastolic blood pressure (DBP) in stepwise regression were controlled for while comparing high and low altitudes using analysis of covariance (ANCOVA).

Results: The three low-altitude samples showed similar values for adult BP after controlling for age and other BP correlates. Age was highly correlated to adult BP for both males and females after adjusting for anthropometric and haematological variables. A similar analysis for children and adolescents showed lower BP values at high altitude.

Conclusion: Lower BP values among Tibetan children and adolescents at high altitude suggest that altitude affects BP as previously hypothesized, but only in youth. Similar BP in adults at low and high altitudes may reflect the effects of other variables on BP. Measures of adiposity (SFT, BMI and MUAC) have a significant effect on BP. Increase in BP with adult age is observed in Tibetans, which is similar to the pattern observed among populations undergoing modernization.