The Global Burden of Disease 2010 study attributed more deaths to high blood pressure than to any other risk factor. Blood pressure is a well-established risk factor for vascular disease, but important questions remain about its importance in different patient groups and for different clinical outcomes.
In 1990, CTSU conducted an overview involving 420,000 participants from 9 prospective observational studies, which demonstrated a continuous relationship between diastolic blood pressure and both ischaemic heart disease and stroke down to at least 70 mmHg. This was the first study to account for random error in blood pressure measurement, which had previously led to a systematic underestimation of the strength of any relationship between blood pressure and disease risk (known as the 'regression dilution bias').
CTSU then played an important role in establishing the Prospective Studies Collaboration (involving one million participants from 61 studies conducted mainly in Europe or North America), to assess the effects of established risk factors on the risks of dying from specific vascular diseases in different circumstances (e.g. at different ages, and at different levels of other risk factors). The meta-analysis showed that blood pressure is a major risk factor for ischaemic heart disease, stroke and other vascular causes of death both in middle and in old age, with about a halving in risk for every 20 mm Hg lower usual systolic (or 10 mm Hg lower diastolic) blood pressure. It also found that there is no threshold level of blood pressure, at least down to 115/75 mmHg (ie, within the range commonly occurring in Western populations), below which lower blood pressure is not associated with lower vascular mortality.
This study influenced treatment guidelines for blood pressure worldwide. It also continues to influence the design of trials to assess the effects of lowering blood pressure in different patient groups.
CTSU is currently involved in work to understand the importance of blood pressure in different populations around the world. In collaboration with local principal investigators, we are conducting prospective cohort studies in China, Mexico, Russia, Cuba and India (Chennai and Trivandrum) (total: 1.7 million participants). We are also working on UKBiobank to understand both the effects and determinants (including genetic) of blood pressure in the UK.
In addition to understanding the effects of blood pressure on major diseases, these cohorts allow an assessment of the burden of hypertension in each country (including levels of diagnosis and treatment) to inform national policies on blood pressure control.