The term ‘essential hypertension’ is used when there is no clear identified medical reason for raised blood pressure. Blood pressure (BP) is determined by cardiac output (i.e. blood ejected by the left ventricle of the heart), peripheral resistance (i.e. force against which blood moves during circulation) and blood volume. An increase in one of these factors will give rise to increased BP if the other influences remain constant. Systolic blood pressure (SBP) is associated with contraction of the heart, whilst diastolic blood pressure (DBP) refers to the force between contractions. Most experts agree on the definition of hypertension, i.e. above 140 mm Hg SBP and/or above 90 mm Hg DBP. Hypertension is a known risk factor for stroke and other cardiovascular events, as well as end-stage renal disease (see Coronary heart disease chapters and ‘Stroke’). In the western world approximately 20% of middle-aged adults suffer from hypertension, with higher prevalence in the elderly (80% of >65-year-old group) and in Afro-Caribbeans (50% in middle age). Hypertension is asymptomatic, and therefore often remains undetected and untreated. In the UK, the state-run health service spent around £840 million ($1.5 billion) in 2001 on prescriptions for antihypertensive drugs, nearly 15% of the total annual cost of all primary care drugs (NoEHGDG, 2004). Certain psychological and behavioural factors have long been associated with the aetiology of hypertension. In fact, only 30%–60% of the variation in essential hypertension in the population can be accounted for by genetic factors (Levy et al., 2000).