Mild high blood pressure: are we treating too many people?

There’s no proof blood pressure-lowering drugs prevent heart attacks in people with mild hypertension – but they could. The Clear Communication.../Flickr, CC BY-NC-ND

An article in this week’s issue of the British Medical Journal calls into question a common practice: treatment of mild high blood pressure.

The authors argue that lowering the drug threshold for high blood pressure has exposed millions of low-risk people around the world to drug treatment of uncertain benefit, at huge cost to the health system: $32 billion annually in the United States alone.

It’s a provocative but thoughtful take on an important issue. But it doesn’t mean you should ditch your blood pressure-lowering drugs. Let’s consider the evidence and what it all means for people with mild high blood pressure.

But first, what is blood pressure, and how high is too high?

Hypertension

Consistently high blood pressure is called hypertension, and medicines used to bring blood pressure down are called anti-hypertensives.

There’s no doubt that hypertension is a major risk factor for diseases like heart attacks and stroke. And there’s good evidence that anti-hypertensive medicines do work – they not only reduce blood pressure but (more importantly) many also reduce the occurrence of strokes, heart attacks and sometimes death.

Like the air pressure in a tyre, blood pressure can be measured numerically. Unlike a tyre, blood pressure swerves up and down with every beat and relaxation of the heart. The two numbers in a blood pressure reading indicate the maximum and minimum levels it veers between with every beat.

While a textbook “normal” blood pressure would be about 120/80, readings vary a lot between people, and even change from minute to minute in an individual. The fickle nature of blood pressure means we needs lots of readings (preferably during normal life rather than in a doctor’s office) to get a reliable average in a given person.

Anti-hypertensives have clear benefits for some people with high blood pressure. Nina Matthews Photography/Flickr, CC BY

Exactly what blood pressure range is acceptably normal is surprisingly hard to answer. Thresholds for high blood pressure used to be more lenient, but for some years now several international guidelines (including Australia’s) have used above 140/90 as the defining threshold for hypertension.

The controversy

We’re confident that several anti-hypertensive medicines reduce risk for people with moderate or severe hypertension (above 160/100), and even for people with normal blood pressure who are at high risk because of a past heart attack.

What’s controversial is whether the medicines benefit people with mild hypertension (140-159/90-99) who’ve not had a heart attack or a stroke. This category includes a lot of people – perhaps over a million Australians.

Central to the new article’s argument is that, when all the available results of trials of anti-hypertensives in people with mild hypertension are brought together, they don’t prove that such treatments save lives or prevent heart attacks or strokes.

Because most previous anti-hypertensive trials studied people with higher average blood pressures, it was hard for analysts to find data on treatment of people with only mild hypertension.

But absence of proof of benefit doesn’t mean we’re sure that treating mild hypertension is useless. It just means that we don’t know.

In fact the data hinted, imprecisely, at possible reductions in death and strokes from treating mild hypertension. Though this impression was not “statistically significant” – it could quite plausibly have been a statistical illusion. Such chance findings happen easily when you measure an uncommon outcome in too few people.

The guidelines for when to prescribe anti-hypertensives are contradictory. World Granny/, CC BY-NC

Such uncertainty is a breeding ground for controversy. The sceptical authors of the new article take the view that, as treating mild hypertension is unproven and costly, and as the medicines can cause side effects, we should be much more cautious about prescribing them in mild hypertension.

On the other hand, advocates of treatment of mild hypertension take the view that too few people with mild hypertension have been studied, for too short a time, to rule out a benefit. Given the proven benefits of anti-hypertensives in other groups of people, they say it may be unethical to study this further, and we should continue treating those with mild hypertension.

It’s a very similar debate to the recent furore around prescribing of statins (cholesterol-lowering pills). Statins are life-savers in patients at high risk, but do they save lives in people at low risk? Some say yes, some say no. While battles erupt in journals and other media, doctors and their patients are left confused.

Adding to the confusion are the inconsistent guidelines which doctors are encouraged to follow. Faced with a middle-aged person with blood pressure of 155/95 and with no other risk factors, one major Australian guideline encourages us GPs to prescribe anti-hypertensives, while another dissuades us from doing so. (Both guidelines are endorsed by Australia’s Heart Foundation.)

What we can all do

First, all of us can try to have a healthy lifestyle: exercising, and avoiding smoking and excessive alcohol and salt. These measures lower blood pressure, but are also good for all of us regardless of our blood pressure.

Second, if you have hypertension, try to engage with your doctor in shared decision-making. Hopefully your doctor will acknowledge what we do and don’t know on this topic.

Many of us should cut down on salt anyway. ilolab/Shutterstock

With your doctor, consider how much risk you are at of heart attacks or strokes. If you’ve already had one of these events, then you are at very high risk, and anti-hypertensives will likely be recommended with confidence.

Otherwise, online tools are available to estimate your “absolute risk”. These tools are based not just on your blood pressure, but also other important factors like age, gender, smoking, diabetes and cholesterol. Mild hypertension alone may not put you at great risk, but it may be more significant when combined with other problems.

If medicines for mild high blood pressure do offer some (as yet theoretical) protection, then they are more likely to do so the higher your risk is. If, for example, a treatment prevented a quarter of some possible nasty events, but your risk of such an event was only 4% over five years, then your chance of the treatment preventing that event is only 1% over those five years.

Personally, I would opt for treatment of mild hypertension if my overall risk was high, but probably not if it was low. But you might make a different decision to me. And that’s OK – we all have different values and preferences.

Finally, there are things that can be done at a population level that can help blood pressure and risk. Some authors suggest worrying less about doctor visits and measurements, and instead just putting everyone over the age of 55 onto a “polypill” containing several low-dose medicines. But this strategy is unproven, and involves an awful lot of pill-popping.

Less radical, and hopefully more acceptable, are policy measures to reduce the health impacts of smoking, alcohol and salt, and to encourage physical activity. Measures like reducing societal inequality, encouraging active transportation and ensuring access to healthy foods might do more good than doctors visits and pills.