July 27 (HealthDay News) -- People over the age of 60, especially those with high blood pressure, may experience a "silent stroke" and won't even know it, Australian researchers say.

"These strokes are not truly silent, because they have been linked to memory and thinking problems and are a possible cause of a type of dementia," study author Dr. Perminder Sachdev, a neuropsychiatry professor at the University of New South Wales in Sidney, said in a news release from the American Academy of Neurology.

The study, published in the July 28 issue of the journal Neurology, followed 477 people aged 60 to 64 for four years. The researchers found that 7.8 percent of the group had evidence of strokes that do not cause any noticeable symptoms -- known as silent lacunar infarctions -- in which blood flow is blocked in one of the arteries leading to areas deep within the brain. An additional 1.6 percent of the study group had experienced silent strokes by the end of the study period.

Those with high blood pressure had a 60 percent greater chance of having a silent stroke than those with normal blood pressure. Also, study participants with a condition called white matter hyperintensities were almost five times more likely to have a silent stroke than those without this small type of brain damage, the researchers found.

Although relatively symptom-free, silent strokes are a major health problem among the elderly, according to the American Academy of Neurology. People who have had a silent stroke are at higher risk for subsequent strokes and for an accelerated loss of mental skills. In addition to high blood pressure, risk factors include diabetes, heart disease, smoking and older age.

In the event that a person is experiencing any symptoms of stroke, call emergency medical services immediately, the academy states. Common signs of stroke are:

• Sudden weakness or numbness of the arms, legs or face, especially on one side
• Quick onset of blurred vision in one or both eyes
• Difficulty walking, dizziness, or loss of balance or coordination
• Sudden confusion or trouble speaking
• Sudden severe headache with no known cause.

SOURCE: American Academy of Neurology, news release, July 27, 2009