Blood pressure is the most widely measured number in medicine and one of the least understood by the people it describes. Millions know their reading and could not say which number is which, what the units refer to, or why a figure that produces no sensation whatsoever is treated as urgent. That last point is the one that matters most: high blood pressure is dangerous precisely because it is silent. It does its damage over years without announcing itself, and the first symptom for many people is the event it caused.
What the Two Numbers Measure
Blood pressure is written as one number over another — 118/76, for example — and measured in millimetres of mercury, a unit inherited from the mercury columns of early instruments.
The top number, **systolic pressure**, is the pressure inside your arteries at the moment the heart contracts and pushes blood out. It is the peak of each cycle.
The bottom number, **diastolic pressure**, is the pressure remaining between beats, while the heart relaxes and refills. It reflects the baseline load your arteries carry continuously.
Both matter. Systolic pressure tends to be the stronger predictor of cardiovascular risk in people over fifty, largely because arteries stiffen with age and the peak climbs. In younger adults, a raised diastolic figure carries more weight.
The Categories
Guidelines differ between countries, and this genuinely confuses people who read advice from more than one source. The American Heart Association thresholds are:
- **Normal:** below 120 and below 80
- **Elevated:** 120 to 129 systolic, below 80 diastolic
- **Stage 1 hypertension:** 130 to 139 systolic, or 80 to 89 diastolic
- **Stage 2 hypertension:** 140 or higher systolic, or 90 or higher diastolic
- **Hypertensive crisis:** above 180 systolic or above 120 diastolic — requires immediate medical attention
European and several other national guidelines set the threshold for hypertension at 140/90 rather than 130/80. This is not a scientific disagreement about the data so much as a difference in where to draw the line for labelling and treating. Under either framework, the direction of the advice is identical: lower is better across the whole range, and the benefit of reduction is continuous rather than switching on at a threshold.
Note also the word "or" in those definitions. A reading of 128/94 is stage 1 hypertension despite a normal-looking top number.
Why It Causes Harm Without Symptoms
Think of the arteries as pipes carrying a pulsing load. Sustained excess pressure damages the delicate inner lining of blood vessels, which accelerates the buildup of plaque. It thickens the walls of the heart's left ventricle, which has to work harder against the resistance, eventually stiffening and pumping less efficiently. It damages the tiny, high-flow vessels of the kidneys, the retina, and the brain.
None of this hurts. There are no nerve endings reporting arterial pressure. The commonly cited symptoms — headache, nosebleeds, dizziness — are unreliable and mostly appear only at extreme levels. This is why the condition is routinely described as a silent killer, and why measurement matters more than how you feel.
How to Measure It Properly
Home readings are genuinely useful, and often more informative than a single clinic reading, because anxiety in a medical setting raises pressure in a well-documented pattern. But technique changes the number substantially — poor measurement can easily add ten points or more.
- Avoid caffeine, exercise, and smoking for thirty minutes beforehand
- Empty your bladder first; a full bladder measurably raises readings
- Sit for five quiet minutes before measuring, back supported, feet flat on the floor, legs uncrossed
- Rest your arm on a table so the cuff sits level with your heart
- Put the cuff on a bare upper arm, not over a sleeve, and check the cuff size fits your arm
- Do not talk during the measurement
- Take two readings a minute apart and average them
- Measure at the same times each day, ideally morning and evening, and record everything rather than only the good numbers
A single high reading is not a diagnosis. Pressure varies through the day and in response to almost everything. Patterns over a week or two are what count.
What Actually Lowers It
The following are the interventions with real evidence behind them, roughly ordered by typical effect size.
**Reduce sodium.** This is the single largest dietary lever. Most guidelines recommend staying under 2,300mg daily, with an ideal target closer to 1,500mg for people with hypertension. The great majority of sodium in most diets comes from processed and restaurant food rather than the salt shaker — bread, cured meats, sauces, soups, snacks and stock cubes. Cutting sodium can lower systolic pressure by roughly 5 to 6 mmHg in people with hypertension.
**Lose excess weight.** Weight reduction has one of the most consistent effects, with roughly 1 mmHg of systolic reduction per kilogram lost for many people.
**Move regularly.** Around 150 minutes of moderate aerobic activity per week — brisk walking counts — typically lowers systolic pressure by 5 to 8 mmHg. Resistance training adds further benefit. The effect requires continuation; it fades within weeks of stopping.
**Increase potassium.** Potassium counteracts sodium's effect on blood pressure. Vegetables, fruit, beans, and dairy are the practical sources. Important exception: people with kidney disease or on certain blood pressure medications must not increase potassium without medical guidance, as high potassium can be dangerous.
**Follow a DASH-style eating pattern.** The Dietary Approaches to Stop Hypertension pattern — heavy on vegetables, fruit, whole grains, legumes, nuts and low-fat dairy, light on red meat, sweets and saturated fat — produces reductions of around 8 to 11 mmHg systolic in trials, comparable to some medications.
**Limit alcohol.** Reducing intake in heavier drinkers lowers pressure reliably. The effect is dose-dependent.
**Address sleep.** Untreated obstructive sleep apnoea is a common and frequently missed cause of hypertension that resists medication. Loud snoring with witnessed pauses in breathing, plus daytime sleepiness, warrants investigation.
**Manage chronic stress sensibly.** The evidence here is weaker and more mixed than the popular framing suggests. Stress produces short-term spikes reliably; its contribution to sustained hypertension is less clear. Reducing it is worthwhile, but it is not a substitute for the items above.
On Medication
Lifestyle change is genuinely powerful and for many people with mildly raised pressure it is sufficient. But hypertension also has strong genetic and age-related components, and needing medication is not a personal failure. Blood pressure drugs are among the best-studied medicines in existence and reduce strokes and heart attacks substantially.
Two points that cause avoidable harm. First, these medications control rather than cure — stopping because the numbers improved allows the pressure to return. Second, many people quietly abandon a drug because of a side effect without telling anyone, when several distinct drug classes exist and switching often resolves it. Raise it with your doctor rather than stopping on your own.
The Bottom Line
Systolic is the pressure when the heart beats; diastolic is the pressure between beats. Below 120/80 is the target most guidelines aim toward, and either number being high is enough to matter. The condition produces no symptoms while damaging arteries, heart, kidneys and eyes, so measurement is the only way to know. Cutting sodium, losing excess weight, walking 150 minutes a week, eating more potassium-rich food and drinking less alcohol are the changes with the strongest evidence — and together they can rival a medication. This article is general information and not a substitute for individual medical advice; discuss your own readings and treatment with a doctor.
Be the first to share a thought.