Think your blood pressure is normal? Think again

The latest iteration of an “ideal” blood pressure – a level of 120mm of mercury for systolic pressure, the top number – that people are urged to achieve and maintain has been called into question by a long-term multiethnic study of otherwise healthy adults.

The study, published in the Journal of the American Medical Association (Jama) Cardiology, found that as systolic blood pressure rose above 90mm, the risk of damage to coronary arteries rose along with it. Systolic blood pressure represents the pressure within arteries when the heart pumps (as opposed to diastolic blood pressure, the lower smaller number, when the heart rests).

The findings suggest a need to look more carefully at why, despite considerable overall improvements in risk factors for heart disease in recent decades, it remains a leading killer.

Although significant progress has been made along several fronts, especially drastic cuts in cigarette smoking and lowered levels of artery-damaging cholesterol, atherosclerotic heart disease still kills far too many people long before they reach their potential life span. If not for a plethora of therapeutic advances, such as antihypertensive drugs, cholesterol-lowering statins and open-heart surgery to bypass clogged arteries, life expectancy would be a lot worse for many people.

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As shown in the study, even levels of blood pressure that are generally considered “normal” may indeed be high enough to foster the development of atherosclerotic heart disease by more than fourfold above the risk faced by people with systolic blood pressures that are physiologically ideal.

Heart experts have long known that people in traditional non-industrial societies typically maintain systolic blood pressures in the low 90s throughout life. Their blood pressure does not rise with age. Rather, it seems, the increase in blood pressure most common among Europeans and Americans as they age in to mid – and late – adulthood is an artefact of our sedentary lifestyles and diets too rich in calories and high in sodium, all of which result in stiff, narrowed arteries that result in high blood pressure.

The study, directed by Dr Seamus Whelton, cardiologist and epidemiologist at the Johns Hopkins Ciccarone Center for the Prevention of Cardiovascular Disease in Baltimore, followed a cohort of 1,457 middle-aged men and women initially free of atherosclerotic vascular disease and known risk factors for 14.5 years. As the participants aged, their risk factors for heart disease increased, along with calcium deposits in their coronary arteries and cardiovascular events such as heart attacks and strokes.

The research team focused on increases in systolic blood pressure with age, adjusting the data for changes in other heart risks. They found that for every 10mm increase in systolic blood pressure, the risk of calcium deposits and cardiovascular events rose accordingly. Compared with people with systolic pressures between 90 and 99mm, those with pressures between 120 and 129mm were 4.58 times more likely to have experienced a cardiovascular event.

Preventive strategies

Still, Whelton said in an interview that it would be wrong to focus preventive strategies on blood pressure alone. People with high blood pressure, he said, “are also more likely to have higher cholesterol and blood glucose levels. The ideal strategy would focus on all risk factors – blood cholesterol, blood sugar and blood pressure. Maintaining a healthful diet, exercising, not smoking and consuming alcohol only in moderation would improve all the risk factors for cardiovascular disease.”

Levels of what doctors consider a healthy systolic blood pressure have been falling for about half a century. In August 1950, a report in Jama suggested that labelling systolic blood pressures of 140, 150 or 160mm as abnormally high is “arbitrary, particularly when age is concerned”. The authors suggested that raising acceptable blood pressure levels for people over 40 “would result in a decrease in the reported incidence of hypertension and thus allay some of the widespread and unnecessary fear regarding high blood pressure”.

Organisations around the world, including the Irish Heart Foundation, list the normal level of blood pressure at about 120 (systolic) over 80 (diastolic). And the Health Service Executive says "around 30-40 per cent of people in Ireland have high blood pressure but many don't know it". The latest blood pressure advisory, issued in 2017 by the American Heart Association and American College of Cardiology, considers a systolic blood pressure of 120mm the upper limit of normal, and defines 130mm and above as high blood pressure that warrants treatment with lifestyle measures or medication.

In an editorial accompanying the new study, Dr Daniel Jones, hypertension specialist at the University of Mississippi Medical Center who helped formulate the current blood pressure guidelines, wrote: "The risk imposed by a blood pressure level below the currently defined hypertensive level is continuous beginning with a systolic blood pressure as low as 90mm mercury."

Jones said in an interview: “Normal blood pressure can be in the 90s, which is what it is in young healthy women, before the vascular system is damaged by elevated blood pressure over the years. Prevention should start with children, with a healthy diet low in salt and regular exercise, and adults should avoid gaining weight with age, which I realise is very difficult to do in our toxic food society.” – New York Times