Introduction
Hypertension is a leading cause of cardiovascular diseases (CVDs) globally and in India. About one-third of all urban and one-fourth of all rural adults in India have hypertension.1 Previous studies by our group have estimated prevalence of hypertension and its risk factors in state-wide representative survey of Madhya Pradesh. We found that prevalence to be 25.7% in urban and 20.8% in rural areas.2 These numbers translate into more than 200 million individuals with hypertension in India.3 Given this huge burden, National Program for Cancer, Diabetes, Cardiovascular diseases and Stroke (NPCDCS) launched by the government of India envisages annual screening for hypertension in all adults above 30 years of age.4 Once such screening is fully operationalised, individuals with newly detected hypertension are likely to add on to the overall burden. There are only a limited studies on incidence of hypertension from India. In a previous cohort of 300 individuals (age range 15–64 years) from southern Indian state of Kerala, India, nearly one-fourth individuals developed hypertension in 7 years of follow-up from 2003 to 2010.5 This 3.3% annual incidence was the only community-based benchmark from India, until publication of a multicity CARRS Study (Chennai, New Delhi and Karachi) in 2017 among adults with age 20 years or more, provided an annual incidence estimate of 8.2%.6 A recently published cohort from eastern state of West Bengal has reported incidence of hypertension among adults of age 18 years or more to be 5.9% for women and 7.9% for men, respectively.7
Rise in incidence has led to increase in prevalence of hypertension and bridging of rural–urban gap.8 In addition to incidence, increased survival and thereby duration of disease can also be attributed to rise in prevalence. It is important to identify risk factors of such incident hypertension beyond age, in case the tide needs to be stemmed. Previous studies have identified elevated blood pressure (previously known as prehypertension) as a key risk factor, which simply indicates a transition from a normal to hypertensive state.5 6 Obesity, smoking, alcohol use and dysglycaemia are other reported significant factors in these two studies from India. Lack of physical activity and increase in alcohol use have been identified as key risk factors in two recent meta-analyses.9 10 The evidence base of incident hypertension and its risk factors is sparse and there is a need to better understand relationships in cohort studies, especially in vulnerable population subgroups.
Two-thirds of population of India is young, and more than half of all adults residing in urban areas are economically disadvantaged.11 These population subgroups are most vulnerable to develop incident hypertension, contributing to overall CVD burden. The current study is designed to estimate incidence of hypertension and its predictors on follow-up. In addition to project future anticipated burden of disease and identification of vulnerable groups, incidence information is also important to assess operational adequacy of NPCDCS in the envisaged annual follow-up surveys.