Blood pressure is written as two numbers. Understanding these readings helps you monitor your cardiovascular health effectively.
Reading Your Blood Pressure
Systolic (120): Pressure when heart beats
Diastolic (80): Pressure when heart rests between beats
Blood Pressure Categories (NHS)
| Category | Systolic | Diastolic | Action |
|---|---|---|---|
| Low | Below 90 | Below 60 | May need treatment if symptoms |
| Ideal | 90-120 | 60-80 | Maintain healthy lifestyle |
| Pre-high | 120-140 | 80-90 | Lifestyle changes needed |
| High (Stage 1) | 140-160 | 90-100 | See GP for advice |
| High (Stage 2) | 160-180 | 100-110 | Treatment usually needed |
| Severe | Over 180 | Over 110 | Seek urgent medical help |
Healthy Blood Pressure
Target: Below 140/90 mmHg (or 130/80 if you have diabetes or kidney disease)
Ideal: Around 120/80 mmHg or below
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Factors That Affect Readings
- Time of day: Usually higher in morning
- Activity: Exercise temporarily raises BP
- Stress: Anxiety increases readings
- Caffeine: Can temporarily raise BP
- Full bladder: Can increase readings
- White coat syndrome: Higher at doctor's surgery
- Arm position: Should be at heart level
How to Take Accurate Readings
- Sit quietly for 5 minutes beforehand
- Don't smoke or have caffeine 30 mins before
- Sit with feet flat, back supported
- Place cuff on bare arm at heart level
- Take 2-3 readings 1-2 minutes apart
- Record all readings with date and time
Risk Factors for High Blood Pressure
- Age (risk increases over 65)
- Family history
- Being overweight
- Too much salt in diet
- Not enough physical activity
- Drinking too much alcohol
- Smoking
- Stress
How Blood Pressure Measurement Works: The Methodology
Blood pressure is measured using a sphygmomanometer, which consists of an inflatable cuff, a pressure gauge, and either a manual stethoscope or an automatic electronic sensor. The cuff is wrapped around the upper arm and inflated to a pressure that temporarily stops blood flow in the brachial artery. As the cuff slowly deflates, the point at which blood begins to flow again (detected by pulsing sounds through a stethoscope or vibrations in an electronic sensor) gives the systolic reading. The point at which blood flow returns to normal and the pulsing sounds disappear gives the diastolic reading.
Readings are expressed in millimetres of mercury (mmHg), a unit that dates back to the original mercury column manometers. Modern digital monitors use oscillometric technology, which detects vibrations in the arterial wall caused by blood flow. These vibrations are analysed by the device's algorithm to calculate systolic and diastolic values. While generally accurate, oscillometric devices can give unreliable results in patients with irregular heart rhythms (arrhythmias) such as atrial fibrillation.
For clinical accuracy, the NHS recommends using a validated monitor. The British and Irish Hypertension Society (BIHS) maintains a list of validated blood pressure monitors. Not all devices sold in the UK meet clinical validation standards -- many cheap wrist monitors, in particular, are unreliable. An upper-arm cuff monitor validated by the BIHS is recommended for home monitoring, with prices ranging from £25 to £60 for reliable devices.
Ambulatory blood pressure monitoring (ABPM) involves wearing a cuff for 24 hours, with the device taking readings every 15-30 minutes during the day and every 30-60 minutes at night. This provides a comprehensive profile of blood pressure throughout daily activities and sleep. ABPM is now the gold standard recommended by NICE (National Institute for Health and Care Excellence) for confirming a diagnosis of hypertension, as it eliminates the influence of white coat syndrome and reveals patterns such as nocturnal hypertension (failure of blood pressure to dip during sleep).
Home blood pressure monitoring (HBPM) is an alternative to ABPM. NICE guidelines recommend taking readings twice daily (morning and evening) for at least 4 days, ideally 7 days. Two readings should be taken at each session, 1-2 minutes apart. The first day's readings are discarded, and the remaining readings are averaged. A home average of 135/85 mmHg or above is considered high blood pressure, which is lower than the clinical threshold of 140/90 because home readings tend to be lower than clinic readings.
UK-Specific Context: Hypertension in the UK
High blood pressure (hypertension) is the single largest risk factor for cardiovascular disease in the UK, contributing to approximately 75,000 deaths annually. According to the British Heart Foundation, around 14 million adults in the UK have high blood pressure, but approximately 5 million of these are undiagnosed. The estimated annual cost to the NHS of treating hypertension and its complications is approximately £2 billion.
The NHS Health Check programme offers free cardiovascular risk assessments, including blood pressure measurement, to all adults aged 40-74 in England who have not already been diagnosed with certain conditions. The check is offered every 5 years and also includes cholesterol testing, BMI measurement, and diabetes risk assessment. Despite being free, uptake remains disappointingly low -- only about 40-50% of eligible adults attend when invited. In Scotland, Wales, and Northern Ireland, similar but differently structured screening programmes exist.
NICE Clinical Guideline NG136 (updated 2023) governs the diagnosis and management of hypertension in the UK. The guideline sets clear treatment thresholds: Stage 1 hypertension (140/90 mmHg clinic or 135/85 home/ABPM) should be treated with medication if the patient is under 80 and has target organ damage, cardiovascular disease, renal disease, diabetes, or a 10-year cardiovascular risk of 10% or more. Stage 2 hypertension (160/100 clinic or 150/95 home/ABPM) should be treated with medication regardless of other risk factors.
The DASH diet (Dietary Approaches to Stop Hypertension), while developed in the US, is endorsed by the NHS and British Heart Foundation. It emphasises fruits, vegetables, whole grains, and low-fat dairy while reducing saturated fat, salt, and sugar. The NHS specifically recommends reducing salt intake to no more than 6 grams per day (approximately one teaspoon). The average UK adult currently consumes approximately 8.1 grams of salt per day, with approximately 75% of this coming from processed foods rather than salt added during cooking or at the table.
Community pharmacy blood pressure services have expanded significantly in England since 2021, with the NHS Community Pharmacist Consultation Service and the Hypertension Case-Finding programme. Over 90% of people in England live within a 20-minute walk of a pharmacy, making these services highly accessible. Pharmacists can provide validated blood pressure checks, offer lifestyle advice, and refer patients to GPs for further investigation if readings are elevated. This service is free at the point of use.
Worked Examples: Blood Pressure Scenarios
Example 1: Interpreting a Home Monitoring Record
A 52-year-old man takes readings for 7 days, twice daily (morning and evening), two readings each time.
Day 1 (discarded): 148/92, 145/90, 142/88, 140/86
Days 2-7 average: Systolic readings average 138, diastolic readings average 86
Assessment: Home average of 138/86 mmHg exceeds the 135/85 threshold. This suggests Stage 1 hypertension. The GP would consider ABPM for confirmation and assess cardiovascular risk before deciding on medication.
Example 2: White Coat Syndrome vs True Hypertension
A 45-year-old woman has clinic readings of 155/95 (high). ABPM over 24 hours shows:
Daytime average: 128/78 (normal)
Night-time average: 112/68 (normal dipping pattern)
Assessment: This confirms white coat hypertension -- elevated in clinic but normal at home. No medication is needed, but annual monitoring is recommended as white coat hypertension may progress to sustained hypertension in 1-5% of cases per year.
Example 3: Impact of Lifestyle Changes
A 60-year-old man with readings of 150/95 makes the following changes over 3 months:
Loses 8kg (potential reduction: 4-16 mmHg), reduces salt to under 6g/day (-2-8 mmHg), walks 30 minutes daily (-4-9 mmHg), reduces alcohol to 14 units/week (-2-4 mmHg).
Combined potential reduction: 12-37 mmHg systolic
New estimated readings: 113-138/78-88 -- potentially within normal range without medication.
Common Mistakes and Tips
Frequently Asked Questions
Should I take my blood pressure medication in the morning or at night?
Recent research, including the large-scale TIME study involving over 21,000 UK patients, found no significant difference in cardiovascular outcomes between morning and evening dosing for most people. The most important factor is consistency -- take your medication at the same time each day to maintain steady blood levels. However, if your ABPM shows nocturnal hypertension (blood pressure that does not dip during sleep), your GP may specifically recommend evening dosing to address this pattern.
Can anxiety cause permanently high blood pressure?
Acute anxiety causes temporary blood pressure spikes, but chronic stress and anxiety can contribute to sustained hypertension over time through mechanisms including increased cortisol production, poor sleep, and unhealthy coping behaviours (alcohol, overeating, smoking). The NHS recommends stress management techniques such as regular exercise, mindfulness meditation, and adequate sleep as part of a comprehensive approach to blood pressure management. If anxiety is causing persistently elevated readings in clinical settings, your GP may recommend HBPM or ABPM for more accurate assessment.
How quickly can lifestyle changes lower blood pressure?
Some changes produce noticeable effects within days to weeks. Reducing salt intake can lower blood pressure by 2-8 mmHg within 2-4 weeks. Regular aerobic exercise can show benefits within 2-4 weeks, with maximum effect at 8-12 weeks. Weight loss produces approximately 1 mmHg reduction per kilogram lost. The DASH diet has been shown to reduce blood pressure by 8-14 mmHg within just 2 weeks. However, these are averages -- individual responses vary, and some people may require medication despite optimal lifestyle changes.
Is low blood pressure dangerous?
Low blood pressure (hypotension) below 90/60 mmHg is only concerning if it causes symptoms such as dizziness, fainting, blurred vision, or nausea. Many fit, young adults naturally have low blood pressure with no ill effects. Symptomatic hypotension can be caused by dehydration, medication side effects (particularly blood pressure medications), standing up too quickly (postural hypotension), or underlying medical conditions. If you experience regular dizziness or fainting, consult your GP. For older adults, postural hypotension is assessed by measuring blood pressure lying down and then standing -- a drop of 20 mmHg or more in systolic pressure is clinically significant.
NHS Blood Pressure Services
- GP surgery: Free blood pressure checks available
- Community pharmacies: Many offer free checks
- NHS Health Check: Free for ages 40-74 (every 5 years)
- Home monitors: Available from £15-60 (BHS validated recommended)
High Blood Pressure in the UK
| Statistic | Figure |
|---|---|
| Adults with high BP | ~14 million (1 in 4) |
| Undiagnosed cases | ~5 million |
| Deaths linked annually | ~75,000 |
| Cost to NHS | ~£2 billion/year |
Lifestyle Changes (NHS Recommended)
| Change | Potential Reduction |
|---|---|
| Lose 10kg weight | 5-20 mmHg |
| DASH diet | 8-14 mmHg |
| Reduce salt to <6g | 2-8 mmHg |
| 30 mins exercise daily | 4-9 mmHg |
| Limit alcohol | 2-4 mmHg |