Despite otherwise appearing to be in good health, more than one in 10 middle-aged adults could have unwittingly suffered a "silent stroke", research has found.
MRI scans of 2,000 people with an average age of 62 revealed evidence of a silent cerebral infarction (SCI) or "silent stroke" in 10.7% of those tested.
The people concerned appeared healthy and suffered from no stroke symptoms. But silent strokes, caused by clots blocking blood flow to the brain, increase the risk of a full-blown stroke and may herald future dementia.
Dr Sudha Seshadri, one of the study authors from Boston University School of Medicine in Massachusetts, said: "The significant relationship between hypertension, elevated serum homocysteine, carotid artery disease and prevalent SCI underscores the importance of current guidelines for the early diagnosis and prevention of hypertension and atherosclerosis and their risk factors."
The study also found a significant correlation between atrial fibrillation, a form of irregular heart beat, and silent stroke.
High blood pressure was also associated with a higher likelihood of silent stroke. Specifically, a high systolic blood pressure – the pressure measured with each heart beat – was a risk factor.
Another characteristic of patients who had suffered a silent stroke was raised levels of homocysteine, a sulphur-containing amino acid in the blood.
The findings are published in the American Heart Association journal Stroke.