“Seeing stars,” “getting your bell rung,” and “knocked for a loop” are everyday phrases often used to describe experiencing a concussion. However, these expressions can downplay that even a “mild” concussion is a traumatic brain injury with the potential for lasting, harmful effects, including dementia. A recent study found that 17% of people who have had a concussion have microbleeds—tiny hemorrhages—in their brains.

The study involved more than 600 middle-aged adults with normal cognitive function. Researchers asked the participants if they had ever experienced a concussion—defined as a blow to the head where they lost consciousness—then assessed their brain health using magnetic resonance imaging (MRI). Then, they gave the participants various cognitive tests and asked about their sleep, mood, and overall health.

They found that more than one-third of the participants had experienced a concussion. Of these, 17% had evidence of brain microbleeds, and the more concussions they experienced, the more microbleeds they had. Those who had experienced a concussion tended to have poorer sleep and more gait disturbances, depression symptoms, and memory deficits than those without a concussion.

Microbleeds are markers of cerebral small vessel disease—age-related blood vessel impairments in the brain. These impairments compromise the blood-brain barrier, contributing to the development of cardiovascular disease, dementia, and stroke.

These findings suggest that even mild concussions damage the brain, increasing a person’s risk of dementia. Other studies have demonstrated that mild concussions cause acute and chronic brain damage, and people who experience three or more concussions tend to exhibit cognitive deficits that worsen with each subsequent concussion.

We’ve covered small vessel disease in great detail: - Listen to researcher Dr. Axel Montagne describe the prevalence of this condition as a cause of dementia. - Read more about the condition in our overview article.