Blood pressure

Blood pressure is measured with an inflatable cuff around the upper arm, either by listening for the sounds of blood flow or with an automatic device. Because readings vary from minute to minute and are affected by activity, posture, caffeine and the setting of the measurement, clinical studies rely on the average of several readings. Systolic and diastolic pressure carry similar information about risk. In the one-million-adult analysis, the average of systolic and diastolic pressure predicted vascular death slightly better than either alone, while pulse pressure (the gap between the two) was much less informative [2].

Different thresholds are used for different purposes. Population surveys commonly define hypertension at 140/90 mm Hg [1]. Treatment trials have compared lower and higher targets; the SPRINT trial compared a systolic target below 120 mm Hg with one below 140 mm Hg [7]. A pooled analysis of 123 trials concluded that the evidence supported lowering systolic pressure to below 130 mm Hg [4].

The NCD Risk Factor Collaboration pooled 1,201 population studies with measured blood pressure from 104 million participants in 200 countries. Between 1990 and 2019, the number of people aged 30 to 79 with hypertension doubled, from 331 million to 626 million women and from 317 million to 652 million men, while the age-standardised prevalence (the rate adjusted for differences in age structure) stayed roughly stable. Prevalence exceeded 50% among men in nine countries and among women in two, mostly in central and eastern Europe, central Asia, Oceania and Latin America [1].

Much hypertension goes undetected or untreated. In 2019, 59% of women and 49% of men with hypertension reported a previous diagnosis, 47% of women and 38% of men were taking treatment, and blood pressure was controlled below 140/90 mm Hg in 23% of women and 18% of men. Treatment rates above 70% and control rates above 50% were reached in South Korea, Canada and Iceland, while in Nepal, Indonesia and some countries of sub-Saharan Africa and Oceania fewer than one in ten people with hypertension had it controlled [1].

The Prospective Studies Collaboration combined individual data on one million adults without vascular disease from 61 prospective studies, covering 12.7 million person-years and about 56,000 vascular deaths. The proportional increase in risk for a given rise in blood pressure was similar within each decade of age down to at least 115/75 mm Hg. The relative effect was about half as large at ages 80 to 89 as at 40 to 49, but because vascular deaths are far more common in old age, the absolute difference in risk was greater in older people. The associations were similar in men and women and for strokes caused by both bleeding and blockage [2].

Life-course analysis of 3,128 Framingham Heart Study participants followed from age 50 found that hypertension shortened total life expectancy and life free of cardiovascular disease. Men with normal blood pressure lived 7.2 years longer without cardiovascular disease and spent 2.1 fewer years living with it, and results in women were similar [3].

Genetic evidence points the same way. Among 438,952 UK Biobank participants, those with gene variants associated with 2.9 mm Hg lower systolic pressure had an odds ratio of 0.82 for major coronary events [8]. High blood pressure is one of the main causes of cardiovascular disease, and its effect adds to that of raised cholesterol.

In the DASH (Dietary Approaches to Stop Hypertension) trial, 459 adults were fed a typical American diet for three weeks and then randomly assigned for eight weeks to that control diet, a diet rich in fruit and vegetables, or a combination diet rich in fruit, vegetables and low-fat dairy with less saturated and total fat. Sodium intake and body weight were held constant. The combination diet lowered systolic and diastolic pressure by 5.5 and 3.0 mm Hg more than the control diet overall, by 11.4 and 5.5 mm Hg in the 133 participants with hypertension, and by 3.5 and 2.1 mm Hg in those without [5].

The DASH-Sodium trial then fed 412 participants the control or DASH diet at high, intermediate and low sodium levels for 30 days each. Lowering sodium reduced blood pressure on both diets, and the effects of diet and sodium added together: compared with the control diet at high sodium, the DASH diet at low sodium produced systolic pressure 7.1 mm Hg lower in participants without hypertension and 11.5 mm Hg lower in those with hypertension [9].

Salt substitutes replace part of the sodium chloride in table salt with potassium chloride. The Salt Substitute and Stroke Study randomly assigned 600 villages in rural China, with 20,995 participants who had a previous stroke or were aged 60 or over with high blood pressure, to a substitute of 75% sodium chloride and 25% potassium chloride or to regular salt. Over a mean of 4.74 years, the substitute lowered the rate of stroke by 14%, major cardiovascular events by 13% and death by 12%, with no significant increase in serious adverse events attributed to high blood potassium [10]. Eating patterns are described under dietary patterns.

Excess weight raises blood pressure, and weight loss lowers it. A pooled analysis of 25 randomised trials with 4,874 participants found that an average weight loss of 5.1 kg lowered systolic pressure by 4.44 mm Hg and diastolic pressure by 3.57 mm Hg, or about 1 mm Hg per kilogram. Trials with average weight loss above 5 kg produced larger falls, of 6.63 mm Hg systolic [6]. See body weight.

A 2023 analysis of 270 randomised trials with 15,827 participants compared types of exercise training. All lowered resting blood pressure, and isometric training, in which a muscle is held under tension without movement as in a wall squat or handgrip hold, produced the largest average reduction [11]. Exercise is covered under exercise and longevity, resistance training and high-intensity interval training.

Alcohol raises blood pressure in a dose-dependent way. In 36 trials with 2,865 participants, cutting down had no significant effect in people drinking two or fewer drinks a day, while people drinking six or more drinks a day who cut their intake by about half lowered systolic pressure by 5.50 mm Hg and diastolic pressure by 3.97 mm Hg [12]. See alcohol.

Obstructive sleep apnoea, repeated blockage of the upper airway during sleep, is associated with hypertension. A pooled analysis of 26 studies with 51,623 participants found odds ratios for hypertension of 1.18 with mild, 1.32 with moderate and 1.56 with severe sleep apnoea, and of 2.84 for resistant hypertension (blood pressure that stays high despite several medicines) [13].

Blood pressure-lowering drugs are among the most extensively tested medicines. A pooled analysis of 123 randomised trials with 613,815 participants found that each 10 mm Hg reduction in systolic pressure lowered the risk of major cardiovascular events by 20%, coronary heart disease by 17%, stroke by 27%, heart failure by 28% and all-cause mortality by 13%, with no significant effect on kidney failure. The proportional benefit was similar whether trials started from higher or lower average blood pressure. Beta blockers were less effective than other drug classes for preventing major cardiovascular events, stroke and kidney failure, and calcium channel blockers were more effective for preventing stroke [4].

The SPRINT trial randomly assigned 9,361 people with systolic pressure of 130 mm Hg or more and raised cardiovascular risk, but without diabetes, to a systolic target below 120 mm Hg or below 140 mm Hg. After one year the average systolic pressure was 121.4 and 136.2 mm Hg in the two groups. The trial was stopped early after a median of 3.26 years because the intensive group had a lower rate of the combined outcome of heart attack, other acute coronary syndromes, stroke, heart failure or cardiovascular death (1.65% compared with 2.19% a year; hazard ratio 0.75) and lower all-cause mortality (hazard ratio 0.73). Serious low blood pressure, fainting, electrolyte disturbances and acute kidney injury were more common with intensive treatment, but injurious falls were not [7].

The link between blood pressure and death comes mainly from observational studies, which cannot fully separate blood pressure from the other characteristics of people who have high readings, although the pooled analysis corrected for the variability of single measurements [2]. The Framingham life-expectancy estimates come from one community in the United States [3].

The diet trials were short, lasting eight weeks and 30 days per diet, and supplied participants' food, so they show what the diets can do rather than what people achieve on their own; the DASH-Sodium authors noted that long-term benefit depends on lasting dietary change [5, 9]. The salt substitute trial was open-label (participants knew which salt they used) and enrolled older adults in rural China, most with a previous stroke [10]. The alcohol trials were small and mostly included men [12], and genetic estimates of lifelong lower blood pressure cannot be assumed to equal the benefit of treatment [8].

Full deep dive: blood pressure.