Could you have a stroke and not know it?

Every 40 seconds, someone in the United States has a stroke, according to the Centers for Disease Control and Prevention (CDC). Every three to four minutes, someone dies of one. But there’s a related condition that’s even more common, and gets comparatively little attention: silent stroke.

Some experts estimate that for every stroke that causes symptoms, there are about 10 silent strokes in the U.S. Though the effects aren’t immediately apparent—many people will never even know they’ve had a silent stroke, unless they happen to get a brain scan for another reason—it can put you at risk for other conditions like dementia.

So, what sets a typical stroke apart from a silent stroke?

Stroke vs. silent stroke

“We generally define a stroke as a sudden onset of neurologic impairment following a vascular insult,” says Olajide Benson, MD, a neurologist and neurocritical care specialist, boarded by the American Academy of Psychiatry and Neurology (ABPN), from Medical City Fort Worth in Texas.

"Vascular insult" means a vessel in your brain is bleeding or being blocked by a clot or sticky plaque buildup. Both bleeds and blockages can damage or destroy healthy brain tissue, causing serious neurological symptoms like:

• Confusion
• Dizziness
• Difficulty speaking or understanding speech
• Face or limb numbness, usually one side of your body
• Trouble walking

Strokes can lead to permanent brain damage or death, especially if not treated quickly enough. If you experience any of these symptoms, don’t wait to see if they’ll clear up—drop what you’re doing and call 9-1-1 immediately.

Silent strokes are caused by brain bleeds or blockages, as well. But they tend to occur in a part of the brain called the white matter and affect subtle processes like memory and reasoning. As a result, they don’t cause symptoms you’ll notice.

“We don't necessarily see the results of a silent stroke in a physical way,” Benson explains. “It typically won’t affect your limbs or movement in a way you can immediately tell.”

It’s important to note that a silent stroke isn’t the same thing as a “mini stroke,” or transient ischemic attack (TIA). A TIA typically has symptoms—like weakness on one side of the body or slurred speech—that resolve within 24 hours, but it may not show up on brain scans. On the other hand, a silent stroke doesn’t normally have outward symptoms, but it will show up on brain scans.

How silent strokes can affect your health

If silent strokes don’t have any immediate, obvious symptoms, why should you care? Why make the effort to prevent them?

Because they can have subtle, long-term effects that could interfere with your daily life and independence. Over time, people who have had a silent stroke may notice:

• Difficulties with reasoning
• Mild-to-moderate memory loss
• Gait changes
• Psychiatric disorders like depression

That's not all. “Silent stroke predisposes the person to stroke itself,” adds Benson. “That is, if you have a silent stroke, your risk of a symptomatic stroke is higher. It can also contribute to vascular dementia, which involves repeated vascular insult to the brain.” With vascular dementia, people tend to have a gradual decline in memory and function.

Reduce your risk of a silent stroke

The steps you would take to lower your stroke risk can also help prevent silent strokes. “Risk factors include high blood pressure, diabetes, a history of smoking, and high cholesterol. So habits that help control those factors, like exercising, quitting smoking, and improving your diet, may reduce your risk,” says Benson.

Here are some tips to help you get started:

Know your numbers

Track your blood pressure and, if you have diabetes, your blood sugar. These are both DIY health checks that can be done from home. If you check your numbers routinely, you’ll recognize when they’re out of range, and can notify your healthcare provider (HCP) promptly.

Get help quitting tobacco

It may take a few tries, but kicking tobacco lowers your risk of illnesses like heart disease, diabetes, stroke, and lung cancer. You don’t have to quit cold turkey or go it on your own. Discuss quit methods with your HCP: nicotine patches, gum, prescription medications, hypnosis, talk therapy, and others. You can also call the National Quit Helpline at 1-800-QUIT-NOW (1-800-784-8669) to learn about support in your area.

Build exercise into your daily routine

Not everyone can spend an hour at the gym each day, but there are clever ways to sneak exercise into even the busiest routine. If you sit all day at the office, take walking coffee breaks with a buddy. Try a standing desk, and aim to take the stairs just once a day. On the top floor? Walk down a few flights and then switch to the elevator. Then, add additional flights to your routine each day. Another sneaky way to move more: Turn housework into exercise.

Many people will go their whole lives without realizing they’ve experienced a silent stroke. While experts don’t suggest screening the entire population for the condition, they do recommend you tell your HCP if you experience any of the subtle symptoms, like mild memory changes. They can then perform memory tests, a physical assessment, and, if necessary, a brain scan to determine the cause of your symptoms.