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Quick quiz: Which of your blood pressure numbers is more important? If you said the top one, you’d be only partially right.

For years, health care providers placed greater emphasis on the top number, or your systolic blood pressure. But recent studies have confirmed that the bottom number, your diastolic blood pressure, also plays an important role in determining your risk of heart attack and stroke.

Systolic and diastolic pressures are actually independent risk factors for cardiovascular disease. You can still be at risk if systolic reading is normal but your diastolic is elevated, and vice versa. 

A Tale of Two Numbers
When the heart beats, it creates pressure that pushes blood through your arteries, veins and capillaries. This pressure is the result of two forces: the blood pumping out of the heart and into the arteries (systolic pressure), and the heart resting between beats (diastolic pressure).

Your blood pressure fluctuates throughout the day. It is affected by many things, including physical activity, foods, stress and sleep.

When everything is working well, your blood vessels are constantly adapting to the body’s changing demands. They can become wider or narrower as needed. This helps keep blood flowing freely, so any increases in blood pressure aren’t too large or long-lasting.

Rising Pressure, Rising Risk
According to American Heart Association guidelines, normal blood pressure is less than 120/80 mmHg. You have hypertension if your systolic pressure is 130 and above, your diastolic pressure is 80 and above, or both. 

In most people, systolic blood pressure rises steadily with age due to narrowing and hardening of the arteries. Diastolic pressure generally peaks by your 60s. Your blood pressure also increases if you are obese; eat a high-fat, high-salt diet; smoke; don’t exercise; or have a condition like diabetes. 

Research has shown that high systolic pressure has a bigger impact on the risk for heart attacks, angina (chest pain), and peripheral artery disease. In contrast, raised diastolic pressure has a greater effect on the risk for abdominal aortic aneurysms.

A study of 1.3 million people published in the New England Journal of Medicine found that systolic pressure above 140 increased the risk for heart attack and stroke by 18%. Diastolic pressure over 90 showed a 6% higher risk.

While systolic pressure does play a greater role in the development of cardiovascular events, it’s important to closely monitor your diastolic pressure as well and take action when appropriate. 

Fortunately, medication and lifestyle changes can lower both numbers. Talk to your doctor about keeping your blood pressure in check.