Older people who have trouble sleeping through the night are at an increased risk of unhealthy changes in the brain, a new study found.

The brain changes are tied to increased risks of strokes and other problems like dementia, the researchers say.

While the study itself is not conclusive, it adds to a growing body of evidence showing that "good quality sleep is important especially when people get older," said lead author Dr. Andrew Lim, of the University of Toronto in Canada.

He and his colleagues report in the journal Stroke that waking up several times during the night - known as sleep fragmentation - is tied to subtle changes in the brain that often can only be confirmed with autopsies.

The new study involved 315 people who had worn activity-tracking monitors at least once while they were alive. The tracker also monitored their sleep. When the people died, at an average age of 90, the researchers were able to study their brains.

Nearly a third of the brains showed evidence of strokes, and nearly two-thirds had at least one area of moderate to severe damage to blood vessels.

The more severe the person's sleep fragmentation was, the greater was their risk of hardening of the small arteries in their brains. The risk of having brain tissue killed in small strokes due to lack of oxygen also increased as sleep fragmentation worsened.

It's possible, Lim said, that "repeated waking during the night could lead to a rise in blood pressure" that could damage the blood vessels. Also, he said, conditions like sleep apnea may play a role in keeping oxygen from the brain.

Lim cautioned that the new study cannot tell whether sleep problems caused the brain damage, or the brain damage caused the sleep problems, or whether something else is to blame.

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Regardless, he and his colleagues write, these changes in the brain are tied to strokes and worsening problems with thinking and body movements.

"At this point in time we don't have hard evidence that treating sleep fragmentation is going to make a big difference," Lim said.

"We have to take a deeper look at what causes - and aspects - of sleep fragmentation are most strongly associated with this type of brain damage," he said.

"I think the take-home point is that this is another reason why people ought to take care of their sleep as they get older," Lim said.