Blood pressure is the amount of pressure that your blood exerts on the blood vessels in your body. As your heart beats, it contracts and relaxes, pushing blood out of the heart to the arteries, which are blood vessels that direct blood to the body.
A blood pressure measurement includes an upper and a lower number, given in units of millimeters of mercury (mmHg). The upper number is your systolic blood pressure, and the lower number is your diastolic blood pressure.
The two numbers of a blood pressure reading represent different readings related to your heartbeat:
- Systolic blood pressure: The pressure on your arteries when your heart contracts, represented by the upper number in a blood pressure reading
- Diastolic blood pressure: The pressure on your arteries when your heart relaxes, represented by the lower number in a blood pressure reading
Systolic pressure is the increased pressure in your arteries with each contraction of your heart. This is the upper number on a blood pressure reading.
What’s Normal, and What’s High?
Normal systolic blood pressure is less than 120 mmHg. Having a high systolic blood pressure, or a reading above 130 mmHg, means the blood vessels are experiencing extra pressure. The heart has to work harder to push blood out.
What Are the Health Implications?
Over time, a consistently high systolic blood pressure, or hypertension, is harmful to health. It increases the risk of outcomes such as:
- Heart attack
- Heart failure
- Stroke
- Kidney disease
- Eye disease
What Causes High Systolic Blood Pressure?
One of the most common causes of systolic hypertension is aging. With aging, the blood vessel walls become stiffer, resulting in a higher pressure. Additional causes of high systolic blood pressure include:
- Medical conditions like diabetes and kidney disease
- Diet high in salt
- Low levels of physical activity
- Alcohol intake
- Certain medications
What About Low Systolic Blood Pressure?
Systolic blood pressure can also be too low, a condition called hypotension. In general, a systolic blood pressure of less than 90 mmHg may be considered low, especially if you have symptoms such as:
- Lightheadedness or dizziness
- Fainting or passing out
- Fatigue
- Nausea
- Blurred vision
Diastolic pressure is a measure of the pressure in your blood vessels during the period when your heart muscle is relaxing.
What’s Normal, and What’s High?
Normal diastolic pressure is less than 80 mmHg. Higher numbers may indicate hypertension.
What Are the Health Implications?
Studies show that high diastolic pressure predicts cardiovascular events like heart attack and stroke independently of systolic blood pressure, though to somewhat of a lesser extent.
What Causes High Diastolic Blood Pressure?
Unlike systolic pressure, diastolic pressure does not increase in the same manner with age.
However, other causes of diastolic hypertension are similar to the causes of systolic hypertension. These include lifestyle habits like lack of physical activity, a high-salt diet, alcohol, certain medications, and other medical conditions like kidney disease.
What About Low Diastolic Blood Pressure?
In general, diastolic readings of less than 60 mmHg are considered low, and may be the cause of low blood pressure symptoms. Some people have low diastolic pressure related to other conditions, such as aortic regurgitation (leakiness of the aortic valve).
Both systolic and diastolic readings are necessary to determine whether blood pressure is at a healthy range. A normal blood pressure is less than 120 mmHg systolic and less than 80 mmHg diastolic. If systolic or diastolic pressure is high, the blood pressure is considered elevated or in the hypertensive range.
| Systolic Blood Pressure (mmHg) | Diastolic Blood Pressure (mmHg) | Category | |
|---|---|---|---|
| < 120 | and | < 80 | Normal blood pressure |
| 120-129 | and | < 80 | Elevated blood pressure |
| 130-139 | or | 80-89 | Stage 1 Hypertension |
| 140 or higher | or | 90 or higher | Stage 2 Hypertension |
| 180 or higher | or | 120 or higher | Hypertensive crisis, requiring medical attention |
Elevations in systolic and diastolic pressure are both associated with health outcomes like heart attack and stroke. But some studies suggest that an elevated systolic blood pressure is more strongly linked to these outcomes.
It’s important to monitor your blood pressure periodically to ensure it’s at a healthy level. Having a high systolic or diastolic blood pressure on more than two occasions means you likely have hypertension, a common but underrecognized condition.
Pharmacies often have a machine available to take your blood pressure. You can also measure your blood pressure at home. Here’s how to get the most accurate reading:
- Avoid smoking, exercise, caffeine, and eating meals for 30 minutes before taking your reading.
- Measure your blood pressure before taking medication for lowering blood pressure. A doctor may also recommend rechecking your blood pressure at least one hour after taking your medication to ensure it’s working.
- Ensure that your bladder is empty.
- Find a quiet place free of distractions.
- Sit upright with your feet and back supported. Uncross your legs.
- Place the cuff around your bare upper arm (not over the sleeve), and support the arm on a surface at the level of your heart.
- Stay relaxed and do not engage in conversation, including active listening or speaking, during the measurement.
- Take two measurements one minute apart, and write down the measurements to share with your doctor.
High blood pressure is a highly treatable condition. A doctor can provide personalized guidance on lowering your blood pressure, but overall, certain lifestyle changes can help lower blood pressure and keep your heart healthy. These include:
- Get regular physical activity: Aim for at least 150 minutes of moderate-intensity exercise per week.
- Eat a heart-healthy diet: Lowering salt intake and increasing potassium intake (through fruits and vegetables) can help lower blood pressure. If you have kidney disease, talk with your healthcare provider about your recommended potassium intake. The DASH diet and the Mediterranean diet are two diets that may help lower blood pressure.
- Avoid smoking: This includes secondhand smoke.
- Manage your weight: Obesity is linked to high blood pressure. If you have extra body weight, losing weight may help lower blood pressure.
In addition to lifestyle changes, medication may also be useful. Many medications can help treat high blood pressure. Your healthcare provider can recommend treatment based on your individual circumstances.
A very high or low blood pressure can be a medical emergency. Seek medical attention immediately for the following symptoms:
- Chest discomfort
- Trouble breathing
- Loss of consciousness
- Signs of stroke, such as weakness on one side of your face or body, difficulty speaking, and confusion
Blood pressure measurement includes a top number (systolic pressure, the pressure as your heart contracts) and a bottom number (diastolic pressure, the pressure as your heart relaxes). These numbers indicate the pressure placed on the blood vessel walls in relation to your heartbeat.
