Long-term effects of socioeconomic status on incident hypertension and progression of blood pressure

Objective: Few data have linked socioeconomic status (SES) to incident hypertension, and little information on the relationship between SES and hypertension are available from developing countries. We thus investigated the long-term effects of SES on incident hypertension and changes in blood pressure in Thailand. Methods: In 1985, baseline data were collected from 3499 participants in the Electricity Generating Authority of Thailand study. Participants were re-examined in 1997, 2002 and 2007. Logistic regression models, Cox-proportional hazard models and time-dependent covariates were used to calculate the relationship between SES and prevalent hypertension in 1985, incident hypertension in 1997 and 2007, respectively. Results: The prevalence of hypertension was 20% and the level of income, but not education, was inversely related to prevalent hypertension. Adjusting for several risk factors, compared to those who had tertiary education, participants who had primary education had 30% increased risk of incident hypertension in 1997 [hazard ratio 1.30, 95% confidence interval (CI) 1.09-1.54] and 20% in 2007 (1.20, 1.05-1.37); both P for trend was less than 0.01. Participants who had higher education also had substantially lower increments in SBP and DBP across 22 years (P < 0.0001 for SBP and P = 0.015 for DBP). Level of income was similarly negatively related to the progression of SBP, with a 3.6 mmHg difference between the highest income group and the lowest (P < 0.0001). Conclusion: Hypertensive counseling and surveillance should be emphasized within socioeconomically disadvantaged populations.