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Blood pressure numbers
Shouldn’t your blood pressure be 100 plus your age?
Many people have probably heard this before! This is an old saying for blood pressure levels and comes from a time when doctors understood less about the risks of high blood pressure. It is not true – an optimal blood pressure level is 120/80mmHg or lower, and high blood pressure is 140/90 mmHg or higher, whatever your age. The lower your blood pressure the lower your risk of heart attack, heart failure, stroke and kidney disease will be.
What is a dangerously high blood pressure?
For almost everyone the risks of high blood pressure affect you in the long term. As high blood pressure usually has no symptoms people often don’t know they have it. Because they don’t know they have it, it is never treated and, over a period of years, the blood pressure remains high and starts to damage the blood vessels. This is when the damage to the blood vessels can lead to a heart attack, stroke, heart failure or kidney disease. So, the important thing is to make sure that you know what your blood pressure is and if it is high that you receive treatment and stick to it.
A small number of people will have a blood pressure at very high levels, above 240/120mmHg for example, and this can cause problems very quickly and it needs to be treated straight away.
Which is more important, the bottom or the top number?
We have discovered that systolic blood pressure (the top number or highest blood pressure when the heart is squeezing and pushing the blood round the body) is more important than diastolic blood pressure (the bottom number or lowest blood pressure between heart beats) because it gives the best idea of your risk of having a stroke or heart attack.
We know, for example, that having a blood pressure of 160/80mmHg is more “risky” than having a blood pressure of 150/90mmHg. Having a raised systolic blood pressure but normal or low diastolic blood pressure is called Isolated Systolic Hypertension (ISH) and carries an increased risk of developing heart attacks or strokes and should be treated.
However, there are some circumstances where diastolic blood pressure may be more important than systolic. For example, some studies suggest that, in people aged younger than 40 years, diastolic blood pressure is a better way of assessing risk. However, younger people are less likely to have a stroke or heart attack, so information on their risk of future problems is limited. It could be that diastolic blood pressure becomes more important when it is very high. There is some evidence to suggest that, for example, a blood pressure of 180/120mmHg gives a greater risk of stroke or heart attack than 180/100mmHg.
The only way to resolve this issue is to obtain data from thousands of patients collected on a systematic basis. The statistical tests to investigate the relative importance of systolic and diastolic blood pressure are immensely complicated. However, current evidence strongly suggests that, over the age of 40, it is systolic pressure that is most important.
Only my top number is high - what does this mean?
This is called isolated systolic hypertension and is more common as people get older. It is important that it is treated even though it is only the systolic number that is raised.