Poorly controlled high blood pressure: the short- and long-term effects

"But I feel absolutely fine." It's a very common reaction in people with high blood pressure, and it's understandable: high blood pressure is almost never something you feel. It doesn't hurt, it doesn't tire you, it gives no warning. That's why so many people have it without knowing, and why others stop their medication the moment they "feel well". It is worth understanding why that feeling is so misleading, what happens to the body when blood pressure stays high — in the short term and the long term — and why, at the same time, it's one of the most rewarding conditions to treat.

The "silent killer": why it doesn't hurt

Blood pressure is the force with which the blood pushes against the artery walls with every beat; we need a certain amount of pressure, and the trouble only starts when it stays too high, day after day. Here's the catch: for many years high blood pressure produces no symptoms at all. That's why it's known as "the silent killer": it does its work quietly, with no pain to put us on alert.

That silence deceives us twice over: many people live with it without ever suspecting, and those who do know tend to neglect it precisely because they can't feel it — "why take a tablet every day if I feel fine?" And there lies the mistake: high blood pressure doesn't cause harm because it hurts, but because it quietly wears down organs that don't complain until the damage is already well advanced.

What "poorly controlled" really means

"Poorly controlled" doesn't mean a one-off scare, but high readings sustained over time. As a rough guide, in clinic the usual threshold for high blood pressure is around 140/90 mmHg, though the target is tailored to each person: current European guidelines tend to aim for somewhat stricter numbers in many patients, above all those with diabetes, kidney disease or a history of heart problems. A useful nuance: clinic readings and home readings aren't judged by the same yardstick. For the readings you take at home, at rest, values below 135/85 mmHg are considered acceptable.

But it isn't only a question of numbers. In practice, it shows up above all in three very human situations:

• Never getting it treated, either because it was never diagnosed or because "I'll ring about that at some point" and time slips by.
• Stopping treatment once things improve, seeing a good reading and assuming it's no longer needed. But that reading is good precisely because the medication is working.
• Never reviewing it, carrying on for years on the same regimen when it may well have fallen short: blood pressure changes as life does.

The short-term effects

In the short term, high blood pressure can make itself known through surges or spikes: a headache — often first thing in the morning and at the back of the head — dizziness or unsteadiness, the odd nosebleed or palpitations. These are warnings worth taking seriously, even if many people never notice them at all.

But what really worries me in the short term isn't those niggles; it's what happens inside when blood pressure shoots up and stays very high: it raises the risk of acute events, namely a stroke (when the blood flow to part of the brain is suddenly cut off — either because an artery is blocked or because a vessel bursts and bleeds, which very high pressure makes more likely) or a heart attack. The logic is simple: the higher it goes and the longer it lasts, the tighter the string is pulled.

The long-term effects: slow, silent damage

And this is the underlying reason not to let your guard down. Picture your arteries as the pipes in a house: if they are forever working under too much pressure, they don't burst all at once, but they wear down little by little. It's slow, silent, cumulative damage that takes its toll organ by organ.

• The heart. To overcome that extra pressure, the muscle thickens (ventricular hypertrophy), like a weightlifter taking on too much load. In time it grows stiff and can fail as a pump (heart failure), predispose you to atrial fibrillation and encourage angina and heart attack (ischaemic heart disease).
• The brain. It's one of the most vulnerable organs: high blood pressure is the leading preventable cause of stroke and, by damaging the smallest vessels, over the years it is linked to cognitive decline and vascular dementia.
• The kidneys. They filter the blood through tiny vessels that the pressure quietly damages; sustained over years, it is one of the major causes of kidney failure.
• The eyes. At the back of the eye I can see, quite literally, the state of your smallest arteries: high blood pressure damages them (hypertensive retinopathy) and can affect your sight.
• The arteries. Throughout the body they stiffen, and the pressure speeds up atherosclerosis (the plaques that narrow and harden the vessels); in places their wall balloons and weakens — an aneurysm.

High blood pressure doesn't break anything all at once: it wears you down little by little, silently, over years. The best time to treat it is always before you can feel it.

The good news: controlling it changes everything

This might sound like a bleak picture, but it's quite the opposite. High blood pressure is one of the most rewarding conditions to treat: controlling it well halts the wear and tear, reverses part of the risk you've built up and prevents most of the complications. A thickened heart can improve. Rarely in medicine do you gain so much simply by doing things properly.

And doing things properly starts with lifestyle, which here is a treatment in its own right: avoiding ultra-processed foods, losing any excess weight, moving every day, cutting back on alcohol or giving it up, not smoking, sleeping well and managing stress. On that foundation, medication when it's needed — neither a failure nor a punishment, but the tool that keeps your arteries safe — does the rest. That said, any change of dose, let alone stopping it, is always decided together in clinic, never on your own. And something essential: measuring properly. A single reading in the clinic tells you little; readings taken at home are far more reliable, along with ambulatory blood pressure monitoring (a 24-hour blood-pressure recording), which shows how your blood pressure behaves as you go about your normal life, even while you sleep.

How it is assessed in clinic

When someone comes in with high blood pressure, your cardiologist's work has several parts. First, confirming it with whatever tests each case calls for; treating on the strength of a single reading is treating blind. It's also worth ruling out possible causes of secondary hypertension — when there is a specific underlying cause behind the high pressure — especially in younger people. Next, looking for whether it has already left its mark on any organ: an electrocardiogram, the heart's electrical side; a colour Doppler echocardiogram (an ultrasound scan of the heart), painless and radiation-free, to see whether the muscle has thickened; and a blood test that looks above all at the kidneys. And, finally, tailoring the treatment to each person, because it isn't a number that's being treated: it's the person in front of you.

So if you've ever been told your blood pressure is "a little high", don't leave it hanging and don't drop it the moment you feel well: that sense of wellbeing is, precisely, the most deceptive part of all. Measuring it, understanding your numbers and looking after them costs little and saves a great deal. Taking care of your blood pressure today means protecting your heart, your brain and the years ahead; and that, when all is said and done, is the best way to prevent both the acute and the long-term complications of high blood pressure.

Sources and further reading

• NHS: high blood pressure (hypertension)
• British Heart Foundation: high blood pressure
• World Health Organization (WHO): hypertension

This article is for information only and does not replace individual assessment or advice from a healthcare professional. For acute symptoms such as severe chest pain, call 112.