Spikes in blood pressure that would previously have been ignored could indicate that someone is at risk of a stroke and needs treatment, new research suggests. Doctors’ guidelines currently recommend using average blood pressure to decide about treatments, rather than looking at variations over time. The new research could mean more people are treated for high blood pressure, and that doctors might be advised to choose different drugs to treat it.

What do we know already?

Blood pressure is a measure of the force with which your blood pushes against the walls of your arteries and veins. You need a certain level of pressure to push blood around your body. Your blood pressure varies throughout the day, and it depends partly on what you’re doing. For example, if you are running, your muscles need more oxygen, so your blood pressure will rise temporarily to meet that need.

If your blood pressure is too high, too much of the time, it can damage the walls of your blood vessels, causing blood clots. This can lead to a heart attack or a stroke.

People with high blood pressure often take drugs to reduce it, in the hope of preventing a heart attack or stroke. Guidelines for doctors say that, because blood pressure can vary quite a lot, doctors should take several measurements and use the average figure to decide whether to treat high blood pressure. So, if you had one measurement that was high, but another two that were normal or low, your average blood pressure might be too low for doctors to recommend taking medicines.

Recently, some doctors have started to question this approach. They argue that occasional spikes in your blood pressure could be harmful, and that doctors shouldn’t ignore them. To find out more, they looked at several big studies covering thousands of people, to see if the amount that someone’s blood pressure varied could predict their chances of having a stroke.

We also know that, while most drugs for high blood pressure do an equally good job of bringing it down, some work better than others to prevent a stroke. The researchers looked at previous studies of blood pressure drugs to see whether the differences in their effectiveness could be explained by how they affect the variability of blood pressure.

What does the new study say?

Researchers found that people whose blood pressure varied the most (sometimes high, sometimes low or normal) were at six times the risk of having a stroke compared with people whose blood pressure remained fairly stable.

Most of the people being studied had already had a stroke or mini-stroke (called a transient ischaemic attack, or TIA), so these people were already at fairly high risk of having another stroke. Also, people who’d had the highest spikes in their blood pressure were more likely to have a stroke, even if their average blood pressure wasn’t high.

When the researchers looked at the effects of different drugs, they found that the drugs that made people’s blood pressure more stable, as well as lower, worked better to prevent a stroke. Drugs that lowered blood pressure, but at the expense of making it more variable, were not as good. The drugs that worked best to prevent stroke were calcium channel blockers, and the ones that worked least well were beta-blockers.

The researchers say that their results should lead to a change in guidelines for doctors about how they diagnose and treat high blood pressure. But two other doctors, writing a commentary in the same medical journal, say the study findings needed to be confirmed by more research before guidelines are changed.

How reliable are the findings?

The researchers looked at some very big, well-run trials, covering many thousands of people. That should make the results fairly reliable. However, the trials included in this research were not designed to look specifically at how much blood pressure readings vary. If you were designing a trial to look at this question, you might include more blood pressure measurements, at different times of the day, to find out more detail about how much blood pressure varies and how much this matters. So, it would be useful to see more research designed to look at this question.

Where does the study come from?

The study looking at effects of different drugs was done by researchers at John Radcliffe Hospital in Oxford. The study looking at variability in blood pressure was done by researchers from several institutions, including John Radcliffe Hospital, Connolly Hospital in Dublin, University College Dublin, Imperial College London, and the University of Gothenburg in Sweden. Both studies were published in The Lancet medical journal, owned by publishing company Elsevier.

What does this mean for me?

Most people in the studies had already had a stroke or mini-stroke. So we’re not sure whether the results would apply to people who are otherwise healthy but recorded one or more high blood pressure measurements.

If you’re already being treated for high blood pressure, it’s worth knowing that some drugs work better than others to prevent a stroke. You may want to ask your doctor about the drugs you are taking. However, sometimes people need to take drugs like beta-blockers for other reasons (for example, if they’ve had a heart attack, or if they have heart failure). So, don’t stop taking beta-blockers as a result of this research.