Blood Pressure Numbers: What Systolic and Diastolic Actually Mean

Blood pressure is the force blood exerts against artery walls. It is written as two numbers because it is measured at two points in every heartbeat.

The two numbers

The top number, systolic, is the pressure when the heart contracts and pushes blood out. The bottom number, diastolic, is the pressure when the heart relaxes between beats. Both are measured in millimetres of mercury.

Most guidelines treat readings consistently at or above 140/90 as hypertension, with several defining a raised-risk band from around 130/80. One high reading is not a diagnosis — pressure rises with stress, caffeine, a full bladder and the clinic itself.

Why it is called silent

Hypertension usually produces no symptoms at all until damage has built up. There is no reliable headache that signals it. Most people find out from a routine measurement.

The harm is mechanical and slow: sustained high pressure stiffens arteries, thickens the heart muscle, strains the kidneys and damages small vessels in the eyes and brain. That is why it raises the risk of stroke, heart attack, heart failure and kidney disease.

What lowers it

Reducing sodium produces a measurable fall in most people, and the main source is usually packaged and restaurant food rather than the salt shaker. Losing excess weight lowers pressure roughly in proportion to the loss. Regular aerobic activity lowers it independently of weight.

Limiting alcohol matters more than most people expect. Potassium-rich foods — vegetables, fruit, beans, dairy — work against sodium. Untreated sleep apnoea is a common driver of hypertension that resists treatment.

Measuring at home

Home readings often predict outcomes better than clinic ones. Use a validated upper-arm cuff, sit with your back supported and feet flat for five minutes first, keep your arm at heart level, and take two readings a minute apart. Write them down.

This article is general health information, not medical advice. Talk to a qualified doctor about your own situation.