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Blood Pressure Basics

The Body Basics series explains common health terms and medical tests. The series begins with blood pressure: a key element of heart health.

Author: Patricia Nicholson

Blood pressure is a key element of heart health. The ‘pressure’ is a measurement of the force exerted on the walls of the arteries as blood circulates through them.

High blood pressure, or hypertension, means too much force is being exerted on the arteries. If the artery walls are stretched too much from excess pressure, they can become weak or damaged, or even rupture.

Ruptured arteries can cause strokes or aneurysms, and damaged arteries can form scar tissue that eventually contributes to narrowed arteries and blockages. That means tissues and organs may not be getting enough oxygenated blood to function properly, and the circulatory system is forced to work much harder to pump blood through the body. The overall result is increased risks to heart health.

What the numbers mean

A blood pressure reading always has two numbers: the systolic and the diastolic. The first number (systolic) represents pressure on the arteries when the heart muscle contracts or beats, forcing out blood. The second number (diastolic) represents pressure on the arteries when the heart muscle relaxes to fill with blood between beats.

The letters mmHg that often appear after the numbers are an abbreviation for millimeters of mercury, which is a unit used to measure pressure.

What’s normal, what’s high

Your blood pressure fluctuates depending on circumstances – for example, it is lower when you are asleep and higher when you are agitated. However, if your blood pressure is consistently higher than recommended, you may have hypertension.

Optimal blood pressure is under 120 systolic and 80 diastolic, according to the Public Health Agency of Canada (PHAC); but the agency defines normal blood pressure as anything lower than 130 systolic and 85 diastolic.

A diagnosis of high blood pressure, or hypertension, means blood pressure consistently over 140 systolic or 90 diastolic. PHAC classifies readings of 130 to 139 systolic and 85 to 89 diastolic as “normal-high.”

You can have high blood pressure based on either your systolic or diastolic pressure (even if the other number is within normal range), or based on both numbers.

What you can do

Many factors affect blood pressure. Some of those factors can’t be changed: genetics, for example, and age (risk of hypertension rises as we get older). But many other factors can be modified through lifestyle changes. These modifiable risk factors include being overweight or obese, having a sedentary lifestyle, smoking, and eating a high-sodium diet.

Steps you can take to help control blood pressure include:

  • becoming smoke-free
  • being physically active
  • keeping a close eye on sodium (salt) intake
  • including plenty of fruit and vegetables in your diet
  • limiting saturated fats
  • drinking alcohol only in moderation

You can find out how much sodium and saturated fat are in different foods by reading the nutrition label. Pre-prepared and processed foods are often surprisingly high in sodium.

Why it matters

Blood pressure is one of the most important factors affecting cardiovascular health in women. Older women are particularly at risk of high blood pressure: two out of five women over age 65 are affected.

High blood pressure is a serious threat to heart health: it triples the risk of heart attack and doubles the risk of stroke.

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A Question of Health

This month's topic: How can I support someone who has been sexually assaulted?
When a person has been sexually assaulted, disclosing and accessing support can be very difficult. While the needs and choices of every survivor are unique, feeling supported when they do disclose the assault can be extremely helpful to their healing process.

  • A publication of:
  • Women's College Hospital