Blood pressure

High blood pressure causes damage to blood vessels

Blood pressure is the force exerted by circulating blood on the inside walls of blood vessels. The pressure wave transmitted by the movement of blood along the arteries with each heartbeat is felt as the pulse. Two components of blood pressure can be distinguished: the highest pressure (systolic blood pressure, SBP) occurs each time the heart pushes blood into the arteries and the lowest pressure (diastolic blood pressure, DBP) occurs when the heart fills with blood. The mean arterial pressure is the average pressure over one complete cardiac cycle. Blood pressure is determined by the interplay of cardiac output and peripheral vascular resistance. Vasoconstriction leads to an increase in total peripheral resistance and blood pressure. The majority of patients with hypertension have a normal cardiac output but a raised peripheral resistance which is determined by the presence of small arterioles (Beevers et al., 2001). An increased blood pressure leads to damage of the arterial walls and to atherosclerosis.

Definition of high blood pressure in current clinical guidelines

High blood pressure, medically referred to as hypertension, is usually defined on the basis of thresholds for systolic and diastolic blood pressure, measured in mmHg. However, systolic and diastolic blood pressure show a continuous, consistent and independent relationship with cardiovascular diseases. Mortality from cardiovascular diseases increases linearly and progressively with increasing blood pressure levels above 115 mmHg systolic and 75 mmHg diastolic, as explained further in the Consequences section (Lewington et al., 2002). Given the continuous nature of this association, any classification of hypertension based on cutoff values is arbitrary. Despite this fact, for practical reasons and to guide clinicians, definitions and classifications of high blood pressure have been issued and continuously modified by major societies and organizations. Recent guidelines have been drafted by:

• the World Health Organisation/ International Society of Hypertension;
• the American Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure; and
• the European Society of Cardiology (ESC) and European Society of Hypertension (ESH).

In addition, most countries, such as, for example, the United Kingdom, France and Germany have adopted national hypertension guidelines and recommendations.

Thresholds for hypertension should only be used under certain conditions

The 2007 ESH/ ESC Guidelines emphasise the arbitrariness of thresholds to classify hypertension. For clinical purposes and to facilitate treatment approaches in daily practice, the guidelines propose a classification scheme that may be used under the following conditions (ESH/ESC Task Force, 2007):

• When SBP and DBP fall into different categories a risk assessment and treatment decision should be made for the higher category;
• Isolated systolic hypertension (only SBP is elevated) should be graded according to the same SBP values indicated for systolic-diastolic hypertension. The association of high SBP with low DBP can be regarded as an additional risk;
• Thresholds for hypertension and the need for drug treatment should be regarded as flexible based on the total cardiovascular risk.

European guidelines recommend different hypertension thresholds than American guidelines

As shown in the tables below, the existing European guidelines recommend different hypertension thresholds than the American guidelines.

European Guidelines for the classification of blood pressure levels (mmHg) (ESH/ESC Task Force, 2007)

Isolated systolic blood pressure should be graded (1,2,3) according to systolic blood pressure values in the ranges indicated, provided that diastolic values are <90 mmHg. Grades 1, 2 and 3 correspond to classification in mild, moderate and severe hypertension, respectively. These terms have now been ommitted to avoid confusion with quantification of total cardiovascular risk.

American Guidelines for the classification of blood pressure for adults (US Department of Health and Human Services, 2004)

High blood pressure is very common

Worldwide, 26.4% of the adult population in 2000 suffered from hypertension. In absolute numbers, 972 million adults had hypertension. These figures are predicted to increase by about 60% to 1.56 billion in the year 2025 (Kearney et al., 2005). As shown in Frequency of hypertension in people aged 20 years and older, the frequency of hypertension varies in different regions of the world and is lowest in parts of Asia and highest in established market economies, former socialist economies, and Latin America and the Caribbean. In established market economies such as Western European countries, North America and Japan, the prevalence of hypertension ranges between 20–50%.

Lack of routine monitoring and methodological differences restrict comparability of data

Comparable, representative and recent data on blood pressure and on the occurrence of hypertension for all EU member states are not available at present. Data on blood pressure are usually not collected in routine monitoring of health indicators, but rather in specific surveys which are often regional. Methodological differences in blood pressure measurement and data collection between countries also restrict the validity of comparing blood pressure data from surveys.

MONICA project shows substantial differences in the prevalence of hypertension between European countries

The most comparable data on blood pressure in different European countries are available from the WHO MONICA project. The project included representative, population-based samples from predefined regions. Blood pressure and other risk factors were assessed in a highly standardized way. The most recent data on blood pressure in the WHO MONICA project originate from the mid-1990s. As shown in Average systolic blood pressure among men and Average systolic blood pressure among women, the mean systolic blood pressure for the age group 35-64 varies considerably across countries and is generally lower in women than in men (WHO MONICA, 2003).

When a threshold of 140/90 mmHg is applied, prevalence of elevated blood pressure ranges from 19% to 60% among men and from 20% to 54% in women (Antikainen et al., 2006). Generally, blood pressure appears to be higher in North-Eastern European countries than in South-Western European countries.

Prevalence of hypertension in European countries is substantially higher than in North America

Whereas MONICA data use regional surveys, data presented in Prevalence of hypertension originate from population-based national surveys in England, Finland, Germany, Italy, Spain, Sweden, Canada and the United States that were conducted in 1988–1999 (Wolf-Maier et al., 2003). Participants in all but one of the surveys were aged 35-74 years (Spain: 35-65). The prevalence of hypertension in the European countries among men, based on the standard cut-off point of 140/ 90 mmHg or use of antihypertensive treatment, ranged from 45% in Italy and Sweden to 60% in Germany. Among women, the prevalence ranged from 31% in Italy to 50% in Germany. The respective data for North America (Canada and United States combined) indicate a much lower prevalence of hypertension in both men (30%) and women (25%). For a more detailed overview see Prevalence of hypertension. Across the whole age range, the Mean systolic and diastolic blood pressure is higher in the combined European countries than in North America.

The validity of the above comparisons between European countries is, however, limited, due to the differences in blood pressure measurement methods, age ranges, survey dates, participation rates and sampling methods (Wolf-Maier et al., 2003).

Blood pressure has declined in most developed countries over the last decades

As shown in the Spot maps of population changes in average systolic blood pressure, mean blood pressure decreased significantly between the mid-1980s and the mid-1990s in most of the 38 MONICA populations (WHO MONICA, 2003).

Individual populations differed considerably, but overall mean SBP (DBP) fell by 2.2 (1.4) mmHg in men and 3.3 (2.2) mmHg in women (Tunstall-Pedoe et al., 2006). Average declines were similar across the whole range of blood pressure readings and were not attributed to more effective medication treatment. Using the 160/95 mmHg and the 140/90 mmHg cut-off points, hypertension prevalence decreased in most of the MONICA populations (Antikainen et al., 2006).

Similarly, hypertension prevalence decreased in the United States until the beginning of the 1990s, but this trend was more recently reversed and the last available data from the NHANES 1999-2002 suggest increasing hypertension prevalence (Hajjar & Kotchen, 2003, Hajjar et al., 2006). The only recent European trend data on blood pressure are the estimations reported by the WHO, as shown in Trends in estimated mean blood pressure among men and Trends in estimated mean blood pressure among women (WHO Global InfoBase, 2008). These estimations show a predicted decrease in systolic blood pressure of 1 to 3 mmHg from 2002 to 2005 and a subsequent increase in many middle and western European countries among both men and women. In eastern European countries and some countries like Germany or Sweden, however, mean systolic blood pressure is expected to remain unchanged over this period.

Awareness, treatment and control of hypertension in the population

Community surveillance that has been carried out in the field of hypertension offers the opportunity to evaluate the awareness, treatment, and control of high BP. Awareness is defined as reporting a diagnosis of high blood pressure. Treatment is defined as the use of antihypertensive medication. Control is defined as a blood pressure below a certain threshold, most commonly below 140/ 90 mm Hg. In national surveys from European countries (see above), awareness among those with BP ≥140/ 90 mmHg ranges from 36% in England and Germany to 52% in Italy (Wolf-Maier et al., 2004).

As shown in Hypertension awareness, treatment and control, the proportion of the population with a BP ≥140/ 90 mmHg receiving antihypertensive treatment varies between 25% in England and 32% in Italy. Overall control of hypertension among those aware of high BP amounts to 5% in Spain and up to 10% in England. Among those receiving antihypertensive treatment, control rates range from 19% in Spain to 40% in the England (Wolf-Maier et al., 2004). Compared to European countries, awareness, treatment, and control of hypertension appear to be substantially higher in the USA and Canada. In all countries, women have higher awareness, treatment and control rates than men. These data originate from 1986-1999 and blood pressure control may have increased since that time. The MONICA study shows that awareness, treatment and control of hypertension increased in the majority of study centres from the mid-1980s to the mid-1990s (Antikainen et al., 2006). More recent population-based investigations from Greece (Psaltopoulou et al., 2004), the Netherlands (Scheltens et al., 2007), and Portugal (Macedo et al., 2005) show awareness, treatment and control rates in the same order of magnitude.

Higher prevalence of high blood pressure among lower socio-economic groups

Analyses from eight nationally representative health surveys in Europe show that elevated blood pressure occurs more frequently in lower educated groups (as an indicator of socio-economic position) than in the higher educated population (Dalstra et al., 2005). This socio-economic difference in the prevalence of elevated blood pressure decreases in later life and is greater among women than among men. Also see EUphocus Health Inequalities.

High blood pressure is a major risk factor for cardiovascular disease

Blood pressure is continuously related to cardiovascular disease. Ischaemic heart disease (IHD) and stroke are the most common consequences of high blood pressure and the most frequent cardiovascular disease in the population. Every 20 mmHg systolic or 10 mmHg diastolic increase in blood pressure doubles the mortality from IHD and stroke at age 40-69 years and increases IHD and stroke mortality at age 70-89 years by 50% (Lewington et al., 2002). For a more complete overview see Ischaemic heart disease mortality rate and Stroke mortality rate in each decade of age versus blood pressure at the start of that decade.

Estimates from observational research and clinical trials suggest that a 10 mmHg decrease in systolic blood pressure (or 5 mmHg decrease in diastolic blood pressure) reduces the risk of IHD by approximately 20 to 25% and the risk of stroke by 30 to 40% (Lawes et al., 2002; Lawes et al., 2004; also see Interventions). This reduction in risk applies to fatal and non-fatal events, to males and females, and across regions.

The proportional association of blood pressure with IHD and stroke is modified by age. As shown in Age-specific hazard ratios the slope of the association is steepest in younger age and flattens with ageing but remains continuous in higher age groups. Between the ages of 40 and 69 years, each increase of 20 mm Hg SBP or 10 mmHg DBP is associated with a doubling in mortality from stroke, IHD and other vascular disease. Between the ages of 70 and 89 years, there is still a strong relationship between blood pressure and mortality, but the order of magnitude is slightly smaller (1.5-fold increase in vascular mortality with a 20/ 10 mm Hg increase in SBP/DBP) This highlights the importance of early Interventions.

High blood pressure is a major precursor for heart failure and further vascular diseases

High blood pressure increases the risk of heart failure two to threefold and accounts for about half of heart failure burden in the general population (Kannel, 2000; Lloyd-Jones et al., 2002). High blood pressure is linked to heart failure in two ways. Firstly, high blood pressure itself leads to structural and functional impairment of the heart muscle resulting in heart failure. Secondly, high blood pressure is a risk factor for coronary heart disease, and heart failure is a common consequence of coronary heart disease (Meredith & Ostergren, 2006).

High blood pressure also increases the risk of peripheral artery disease, and end stage renal disease (ESH/ESC Task Force, 2007). High blood pressure can further harm blood vessels in the eye and lead to eye disease. In summary, high blood pressure is a major risk factor for an array of cardiovascular diseases.

High blood pressure affects cognitive function

High blood pressure is associated with cognitive impairment. Cognitive decline and dementia occur more frequently in persons with high blood pressure, due in part to the intermediate outcomes of blood pressure, such as cardiovascular disease and in particular stroke (so-called ‘vascular dementia’) (Staessen et al., 2007). Long-term studies show that raised systolic blood pressure in midlife increases the risk of dementia in late-life (Freitag et al., 2006; Kivipelto et al., 2001). High blood pressure not only raises the risk of vascular dementia but appears to be also a risk factor for dementia of Alzheimer’s type (Breteler, 2000; Staessen et al., 2007).

High blood pressure is a major component of global cardiovascular risk

It is important to look at high blood pressure in the context of total cardiovascular risk. In the majority of cases, high blood pressure is accompanied by other risk factors. See Ischaemic Heart Disease- Causes and risk factors for an overview of these other risk factors. The various risk factors for cardiovascular disease act in an interactive manner and together determine the total cardiovascular risk. As can be seen from Absolute risk of cardiovascular disease over 5 years, the absolute risk for otherwise healthy individuals is small, even at a very high systolic blood pressure level, but increases dramatically with the presence of additional risk factors. Therefore, high blood pressure should not be regarded as an isolated risk factor but in the context of other risk factors.

High blood pressure may be responsible for half of disease burden from coronary heart disease and stroke

Globally, about 47% of IHD and 54% of strokes may be attributable to suboptimal systolic blood pressure exceeding 115 mmHg (Lawes et al., 2008). Estimates from INTERHEART, a worldwide case-control study on coronary heart disease, indicate that 22% of IHD in Western Europe and 25% of IHD in Central and Eastern Europe may be due to a history of high blood pressure(Yusuf et al., 2004). The reliability of these data is, however, limited, both because high blood pressure in this study was reported rather than measured and because the case-control design is prone to bias.

Data from 600,000 participants in the Asia-Pacific Cohort Studies Collaboration, using the common hypertension definition of blood pressure >140/ 90 mmHg, reveal that 4 to 28% of IHD in men and 8 to 39% in women may be caused by hypertension. The corresponding ranges for haemorrhagic and ischaemic stroke among males were 18 to 66% and 8 to 44%, and 15 to 49% and 12 to 45% in females (Martiniuk et al., 2007). It should be noted, however, that these data cannot be directly translated to the European region, due to differences in hypertension prevalence, disease incidence and stroke subtypes.

High blood pressure is the leading risk factor for mortality worldwide

High blood pressure is the most important risk factor in terms of attributable mortality worldwide. Estimates from the WHO GBDS indicate that approximately 13% of global mortality may be attributed to high blood pressure translating into more than 7 million deaths per year (Lopez et al., 2006).

In developed countries, the impact of high blood pressure on mortality is estimated to be even more important. According to the GBDS, 20.1% of deaths among males and 23.9% among females in the European region and other developed countries may be due to high blood pressure (WHO, 2002d). Mortality attributed to high blood pressure is equally distributed between males and females (49 vs. 51%) and occurs mainly in older age (81% at age 60 years and older vs. 19% at age 15-59 years) (Rodgers et al., 2004).

High blood pressure is a leading cause of loss of healthy life

In terms of DALYs, an indicator for loss of healthy life, high blood pressure is the second major cause of disability worldwide next to childhood underweight (Lopez et al., 2006).

The GBDS estimates that 5.6% of DALYs in low-and middle income countries and 9.3% in high-income countries are attributable to high blood pressure. Estimations for the WHO European Region show that high blood pressure is the leading cause of disability in this region accounting for 12.8% of total DALYs (WHO, 2002d]. See also Shares of seven leading risk factors in the DALY burden.

The majority of disease burden from suboptimal blood pressure occurs in middle-age groups

A study analysing the global disease burden from systolic blood pressure greater than 115 mmHg estimates that approximately two thirds of the disease burden occurs in the age-group 45-69 years (Lawes et al., 2006). About half of this disease burden occurs in individuals with systolic blood pressure levels between 130 and 150 mmHg.

High blood pressure is caused by underlying disease in minority of cases

In 95% of cases no identifiable cause of high blood pressure is found and the condition is diagnosed as ‘essential hypertension’. In the vast minority of cases (between 2% and 5%), particular diseases such as kidney disease or adrenal disease cause hypertension and the condition is labelled ‘secondary hypertension’ (Messerli et al., 2007). For a complete overview see the list of identifiable causes of hypertension.

If the cause cannot be identified, high blood pressure may be due to an unfavourable lifestyle or particular risk factors.

Age is a major determinant of high blood pressure

In westernised societies, blood pressure progressively increases with ageing beginning in childhood. Systolic blood pressure increases linearly with age whereas diastolic blood pressure peaks at age 50 to 60 years and declines in later life (Franklin et al., 1997). Also see: Mean systolic and diastolic blood pressures.

The age-related pattern of blood pressure is seen in both men and women, but there is a gender difference, with women starting at a lower blood pressure level than men and catching up by the sixth decade. Given the age dynamics of blood pressure, 50 to 80% of the European and North American population aged 65 to 74 years can be classified as hypertensive using the 140/90 mmHg threshold (Wolf-Maier et al., 2003). Also see: Hypertension prevalences by age group.

Data from the Framingham Heart Study indicate that the residual lifetime risk of hypertension in middle-aged individuals without evidence of high blood pressure is 90% (Ramachandran et al., 2002).

The age-related increase in systolic blood pressure is mainly responsible for increasing incidence and prevalence of high blood pressure with ageing (Franklin et al., 1997). Systolic hypertension is the predominant form of hypertension in middle-aged and elderly individuals (Franklin et al., 2001).

Therefore, from age 50 onwards, systolic blood pressure is the more powerful cardiovascular risk factor, whereas diastolic blood pressure is more important in the younger population.

Physical inactivity and overweight promote high blood pressure

Several lifestyle related factors have been identified as important risk factors for high blood pressure.

Physical exercise and body weight have an influence on blood pressure level. There is sound evidence that physical activity contributes to a reduction of blood pressure (Whelton et al., 2002; Cornelissen & Fagard, 2005). Overweight and obesity are important risk factors for high blood pressure. An increase in body mass index leads to an increase in both systolic and diastolic blood pressure (Drøyvold et al., 2005; Wilsgaard et al., 2000; Gelber et al., 2007).

Unhealthy diet contributes to high blood pressure

Dietary components, particularly insufficient fruit and vegetable intake, high consumption of saturated fat, low fish intake, and high sodium and low potassium intake are related to high blood pressure. Dietary patterns based on the so-called DASH diet, a diet rich in fruits, vegetables and low-fat dairy products, have proven to lower blood pressure (Sacks et al., 2001). Epidemiological studies suggest that dietary salt intake is directly related to blood pressure elevation (WHO/FAO, 2002). Increased fish intake (or supplementation of fish oil) have been shown to lower blood pressure (Dickinson et al., 2006; Bao et al., 1998). Coffee consumption may slightly increase blood pressure (Noordzij et al., 2005), but long-term effects on hypertension incidence seem to be very small (Uiterwaal et al., 2007; Hu et al., 2007).

Alcohol consumption increases blood pressure

Alcohol consumption is directly associated with blood pressure. The relationship between alcohol intake, blood pressure level, and hypertension prevalence in populations is almost linear ( Puddey et al., 1997, Keil et al., 1998). While drinking light to moderate amounts of alcohol has been shown to be protective in terms of cardiovascular mortality (see Positive effects of low-level alcohol consumption), higher alcohol intake leads to excess mortality and is a cardiovascular risk factor (Rimm et al., 1999, Corrao et al., 2000).

Until recently there was a general consensus that light to moderate amounts of regular alcohol consumption do not seem to have a negative impact on blood pressure (Marmot et al., 1994, Fuchs et al., 2001), but this finding has been questioned in a recent study (Chen et al., 2008). Binge drinking, or drinking high amounts of alcohol at one occasion, has, however, been associated with a particularly high risk of stroke reflecting a substantial blood pressure increase (ESH/ESC Task Force, 2007).

Impact of stress and psychosocial factors on high blood pressure is not yet clear

The relationship between stress, psychosocial factors and high blood pressure is complex and not yet fully understood. However, a growing body of evidence suggests that psychosocial factors play a role in the development and onset of high blood pressure (Kaplan & Nunes, 2003). For example, blood pressure reactions to stress can predict future blood pressure elevation (Carroll et al., 2003, Carroll et al., 2001). Depression can also be predictive of hypertension development (Davidson et al., 2000, Jonas et al., 1997, Jonas & Lando, 2000), as can exposure to noise, which is also a known stressor. Recent studies showed that blood pressure increases with exposure to road traffic noise (Bluhm et al., 2007, De Kluizenaar et al., 2007), occupational noise (Sbihi et al., 2008), and aircraft noise (Eriksson et al., 2007, Haralabibis et al., 2008).

Genetic determinants of high blood pressure are unclear

Some genetic abnormalities associated with rare types of hypertension have been identified recently. Despite these findings, genetic abnormalities have not been found to be responsible for an appreciable proportion of the burden of high blood pressure in the population (US Department of Health and Human Services, 2004).

Impact of lifestyle on hypertension prevalence is substantial

Population-based data from selected countries (Finland, Italy, the Netherlands, United Kingdom, and USA) have been used to estimate the burden of hypertension attributable to overweight, dietary components, and physical activity (Geleijnse et al., 2004). Overweight was the most important contributor to hypertension in all countries except Italy (range 11-25% of hypertension due to overweight depending on country). If the effects of additional risk factors are taken into account, around 40% of hypertension prevalence (depending on the population) can be subscribed to overweight, diet, and physical inactivity. It should, however, be noted that these data are based on estimations that have been derived from simplified models. While the findings of this study should therefore be interpreted with caution, they do indicate that selected lifestyle factors have a major impact on hypertension prevalence in populations.

Lifestyle changes are important in the prevention and management of hypertension

There is ample evidence that lifestyle changes lower blood pressure and can prevent the onset and progression of hypertension. A healthy lifestyle is the cornerstone of hypertension prevention and management. Lifestyle changes with documented efficacy include weight loss, increased physical activity, modification of diet such as increased fruit and vegetable consumptions, dietary sodium restriction, and moderation of alcohol consumption (Whelton et al., 2002b). For a complete overview see Lifestyle modifications for hypertension prevention and management.

Even moderate weight loss lowers blood pressure

Weight loss is important for the prevention and treatment of hypertension. Weight loss, achieved by energy restriction, physical activity, or both, transfers directly into blood pressure reduction. Pooled data from intervention studies show that both systolic and diastolic blood pressure decrease approximately 1 mmHg per kilogram of weight loss (systolic BP -1.05 mmHg, diastolic BP – 0.92 mmHg) (