Incidence of hypertension and its risk factors in rural Kerala, India: A community-based cohort study

Summary

Objectives

To investigate the incidence of hypertension and its risk factors in Kerala, India where the epidemiological transition is more advanced than elsewhere in India.

Study design

Prospective cohort study.

Methods

A sample of 297 individuals (aged 15–64 years) in rural Kerala, India, who were free of hypertension at study enrolment, were followed-up from 2003 to 2010. At enrolment, demographic characteristics and behavioural risk factors were determined by interview, and the participants underwent physical (blood pressure, height, weight and waist circumference) and biochemical examinations (fasting plasma glucose and serum lipids). At follow-up, blood pressure readings were repeated using the original tool following the same protocol.

Results

Nearly one-quarter (23.6%) of the sample developed hypertension over a mean follow-up period of 7.1 (standard deviation 0.2) years. Age ≥35 years [relative risk (RR) 4.00, 95% confidence interval (CI) 2.37–6.03], current smoking [RR 1.99, 95% CI 1.14–2.97, population-attributable risk percent (PAR%) 13.3%], high–normal blood pressure (RR 3.53 vs optimal blood pressure, 95% CI 2.17–5.28, PAR% 44.0%) and central obesity (RR 2.45, 95% CI 1.45–3.70, PAR% 40.4%) were significantly associated with incident hypertension. Collectively, current smoking, high–normal blood pressure and central obesity accounted for 70.1% of all new cases of hypertension. Awareness, treatment and control rates of incident hypertension were 42.9%, 22.9% and 11.4%, respectively.

Conclusions

This rural sample showed a high incidence of hypertension. This underscores the need for primary prevention of hypertension through lifestyle modification strategies targeting individuals with high–normal blood pressure, central obesity and current smoking. The healthcare system needs to improve the level of awareness, treatment and control of hypertension in this population.

Introduction

Globally, hypertension is the single most important risk factor for mortality and the third highest cause of morbidity.¹ The world’s adult population with hypertension is projected to increase from 972 million in 2000 to 1.56 billion by 2025.²

Cardiovascular diseases are the leading cause of death in India,³ and hypertension is a major risk factor for coronary heart disease and stroke in the Indian population.⁴ Of the eight world regions defined by the World Bank, India was ranked third in terms of the number of adults with hypertension in 2000, and will retain this position for the next 25 years.²

Kerala is a state in southern India with a population of 33.4 million⁵ and a life expectancy at birth of 74.6 years⁶ (Indian average 61 years).⁷ The epidemiological transition in Kerala is more advanced than that in other Indian states.⁸ Several major cardiovascular risk factors are more common in Kerala than elsewhere in India,9, 10, 11 and Kerala is a forerunner to the rest of India with regard to the burden of non-communicable diseases.¹²

Several surveys have reported the prevalence of hypertension in India,¹³ but data on its incidence are limited.14, 15 The existing data are from the late 1980s to the early 1990s; older criteria was used to define hypertension and the risk factors were not well studied.14, 15 Therefore, this study aimed: (1) to investigate the incidence of hypertension and its risk factors in rural Kerala; (2) to estimate the population-attributable risk percent (PAR%) for the modifiable risk factors; and (3) to assess the awareness, treatment and control rates of incident hypertension.