Still waters that run deep may hold true even for diseases. One may claim he never had a stroke without knowing he's already had multiple "silent" strokes in the past. For one, silent strokes either have no easily recognizable symptoms such as one-sided paralysis, difficulty speaking, or headache after a stroke, or one who's had them doesn't remember such stroke happened.

Another condition that is easily unnoticed is atrial fibrillation, which is a problem with the rate or rhythm of the heartbeat, and where the heart can beat too fast, too slow, or with an irregular rhythm. The most common signs of the condition are dizziness, weakness, and fatigue.

A recent review suggests that atrial fibrillation may more than double the risk of silent strokes. This abnormal rhythm in atrial fibrillation allows blood to pool and coagulate in the heart, forming clots that can cause a stroke, according to the researchers.

Their study which is a meta-analysis had the researchers review 11 previously published reports that looked at the association between atrial fibrillation and silent strokes in 5,000 patients.

In a meta-analysis, researchers evaluate previously published studies to look for patterns that support a conclusion or trend. The conclusions are said to be strengthened in a meta-analysis compared to a single study.

Review author Dr. Shadi Kalantarian, a resident at the Yale School of Medicine said, "Patients with atrial fibrillation are at higher risk of developing silent strokes."

More than 2.7 million Americans, many of them elderly, experience atrial fibrillation, according to background information in the report.

Also, recent research has shown that atrial fibrillation is associated with a 40 percent increased risk for mental impairment, according to US News Report.

"Previous studies have found that silent strokes are associated with more than threefold increase in the risk for symptomatic stroke and a twofold increase in the risk for dementia," she added.

"The higher prevalence of silent strokes in patients with atrial fibrillation may put this population at a higher risk for mental impairment, future stroke and disability," Kalantarian said.

Silent strokes, though usually unnoticed, may lead to brain damage. Among the risk factors of the disease are high blood pressure and irregular heartbeat.

The damage that occurs is permanent, but therapy might help one regain functions that may have weakened, using other parts of your brain, according to WebMD.

The study may have found a link between atrial fibrillation and an increased risk of silent strokes, but it still has not proven a cause-and-effect link.

The report was published Nov. 4 in the Annals of Internal Medicine.

While we may not fully be aware of what's going on inside our bodies, it is better to adopt a healthy lifestyle like getting regular exercise, eating a healthy diet, regularly monitoring one's blood pressure and cholesterol, and quitting smoking, among others, to prevent these silent killers.