What is high blood pressure? Medicine keeps moving the goalposts in trying to define unsafe levels, particularly now that the US has just raised the threshold for starting drug therapy
Do you have high blood pressure (hypertension) that has the doctor reaching for his prescription pad? Surprisingly, there's no agreement in medicine about what a dangerous reading looks like, and it's just got more complicated with the US changing the goalposts again from this year. This time, though, and for the first time ever, they are relaxing the criteria for starting drug therapy.
Up to last December, a dangerous high blood pressure (BP) reading was 140/90 mmHg-the first figure is the systolic pressure, when the heart contracts to pump blood, and the second is the diastolic reading, when the heart is at rest, and measured in millimetres of mercury-but in January, this level was redefined as 150/90 mmHg in the US for everyone aged 60 or over, the group which is taking the majority of antihypertensive agents such as ACE (angiotensin-converting enzyme) inhibitors.1
Even then, says the Eighth Joint National Committee (JNC 8), American doctors should be recommending a healthy diet, weight control and exercise before prescribing a drug. In fact, the committee states, there's only "moderate" evidence to suggest drugs help reduce hypertension.
In the UK, a high BP reading is still
set at 140/90 mmHg, although it too
may follow the US's more relaxed definition soon.
Raising the bar also means fewer people will be taking beta-blockers, antihypertensive agents that may be a killer, new research has suggested. Researchers estimate that around 800,000 people across Europe have died over the past few years from stroke and hypotension (dangerously low blood pressure) after taking these drugs. Yet, within hours of these findings being posted on the website of an academic journal, they were removed.
High blood pressure through the decades
Medicine continually changes its mind over what exactly constitutes high blood pressure and the thresholds for which medication is prescribed. The cut-off definition of high and low blood pressure shifts every decade, as shown below.
The first figure is the systolic pressure, when the heart contracts to pump blood; the second is the diastolic reading, when the heart is at rest (> means greater than;
<= means less than or equal to).
o 1960s: > 100 + age/100 mmHg
o 1980s: > 160/100 mmHg
o 1990s: > 140/90 mmHg
o 2014 hypertension (US): > 150/90 mmHg
o 2014 healthy: <= 120/80 mmHg
Raising the bar
The uncertainty over safe blood pressure levels is strange for a condition that is often dubbed 'the silent killer'. It's reckoned to be a significant risk factor for conditions like heart attack, heart failure, stroke and kidney disease, and the UK's National Health Service (NHS) estimates it affects around 30 per cent of the adult population, with many of them not even realizing they have it-hence the 'silent' epithet. Essentially, high blood pressure puts too much stress on the heart and arteries and can, over time, cause damage to them.
But then, determining what high BP is has always been a thing of fashion as much as science. Less than 50 years ago, doctors used a simple rule of thumb to determine whether the patient's health was at risk. As blood pressure tends to rise with age, the old measure was to add 100 to the patient's age, so an acceptable upper systolic limit for a 60-year-old
This was considered too arbitrary and dangerous-although there's not much evidence to suggest more people were dying then as a result of hypertension-and a more definitive reading of 160/100 mmHg was set for all age groups. Eventually, this too was considered too cavalier, and the current danger level of 140/90 was agreed upon in 1997-until the JNC 8's surprise declaration last December.
Made up of 17 of the US's leading cardiologists and experts on hypertension, the JNC assesses best-practice guidelines by analyzing the results of 'gold-standard' studies. It was at pains to explain that it had not redefined high blood pressure-although that is clearly what it did. "The 140/90 mmHg definition from the Seventh Joint National Committee remains reasonable," the panel states, but it then goes on to say that an even more reasonable reading for someone aged 60 and over should be 150/90 before anyone hits the panic button.
However, the previous threshold remains the best for anyone aged 30 or younger, or with diabetes or chronic kidney disease, the group says.
Even then, doctors should first be advocating lifestyle changes before resorting to an antihypertensive drug. The evidence for taking an antihypertensive-whether an ACE inhibitor, angiotensin II receptor blocker, beta-blocker or thiazide-type diuretic-is only moderate, they say; in other words, any indisputable evidence that they definitely work just isn't there. Instead, they should be used as secondary therapy and only if lifestyle changes don't work or aren't adhered to. The one exception is black patients, for whom there is more solid evidence to suggest that an antihypertensive could be started straightaway in cases with a high BP reading.
In another important guideline shift, the committee questions the current so-called healthy BP reading of 120 mmHg of systolic pressure. This was because they could find little decent evidence to suggest any health risks for readings of 140 or below, they said.
Check it yourself
Your blood pressure normally rises and falls throughout the day. It's at its highest in the morning, and it can also vary from one arm to the other.
But perhaps the best-known phenomenon is 'white-coat hypertension'. Your systolic reading-the first of the two numbers, assessed when the heart is pumping-can rise by as much as 30 mmHg if you are sitting waiting anxiously for the doctor to take a reading. Doctors are supposed to take this into account when they assess whether or not you need to start a course of antihypertensive drugs, but much depends on the doctor and how much he or she toes the line.
If you're worried about getting a false reading-and so starting drugs you don't actually need-you can monitor your own blood pressure by regularly checking it throughout the day at home. The best devices are the fully automatic digital monitors that measure your blood pressure at the upper arm rather than wrist or finger. Be sure to measure your upper-arm circumference carefully and order the right size of cuff for your arm. Companies like Microlife, A&D Instruments, Boots, Braun, Citizen, Health and Life, Honsun (Suresign), Kinetik, Lloyds Pharmacy, Omron and Panasonic all make monitors that have been clinically approved.
Not only is the evidence only moderate that antihypertensives work, but other evidence for the beta-blockers suggests they can be a killer. Their potential for harm came to light only after researchers discovered how they had been given to all patients undergoing surgery-including non-heart surgery-to reduce stress on the heart.
However, the practice, which was adopted across Europe in 2009, was based on fabricated data and research. The falsifications, perpetrated by Don Poldermans, formerly professor of cardiology at the Erasmus Medical Centre in Rotterdam and former chairman of the European Society of Cardiology (ESC) guidelines committee, were uncovered in 2011.
In the two intervening years, hospital patients having surgery were 27 per cent more likely to die from stroke or hypotension after taking a beta-blocker, estimate Darrel Francis, professor of cardiology at Imperial College London, and Graham Cole, a clinical research fellow in cardiology.2
Since then, Francis and Cole have gone on to estimate that the practice has killed 800,000 people across Europe, including 10,000 Britons. These findings were published on the website of the ESC's European Heart Journal in January, but was removed within hours of the post appearing.
Defending the action, the journal's editor, Thomas L"uscher, said publishing Francis and Cole's estimates had been a mistake. "This issue is complex and should not be handled like that. Such statements are not scientifically valid and create panic among patients and physicians, and in this form are not only completely inappropriate but ethically questionable," he said.3
Keeping it in check
High blood pressure is a symptom of our modern way of life. Processed foods and a sedentary lifestyle can all add up to an unhealthy blood pressure reading.
As America's Eighth Joint National Committee has confirmed (see main story), antihypertensive drugs have only "moderate" levels of success and are perhaps best as a short-term remedy if you aren't diabetic or have kidney disease. There's also a question mark over the safety of
Instead, eat plenty of fresh vegetables and fruit, avoid processed and pre-prepared meals, and start exercising.
JAMA, 2013; doi: 10.1001/Jama.2013.284427
Heart, 2013; doi: 10.1136/heartjnl-2013-304262
The Sunday Times, 26 January 2014; www.thesundaytimes.co.uk/sto/news/uk_news/Health/article1367722.ece