Warning to bad sleepers: Tossing and turning even in early middle age spikes risk of memory problems later in life, study reveals

Waking up during the night, even in middle age, can lead to memory problems later in life.

One study looked at people in their mid-30s to late 40s who were fitted with trackers on their wrists to measure their sleep over six days and nights.

Researchers calculated how restless these people were at night based on the percentage of time they spent moving, which indicates they woke up.

Those with the most interrupted sleep, compared to those with the least sleep, were more likely to do poorly in a series of tests about a decade later.

For example, people with the worst sleep quality were more than twice as likely to score poorly on the Montreal Cognitive Assessment.

This important test of thinking skills includes asking people to remember a list of words and do mental arithmetic after a delay.

Experts suspect that people who wake up frequently, perhaps due to work stress or a noisy or bright sleep environment, are worse at clearing potentially harmful proteins in their brains during sleep.

Even in middle age, in your 30s and 40s, this can affect thinking skills later in life.

The study, which involved 526 people, found that those with the most interrupted sleep were almost 2.5 times more likely to perform poorly on tests of their word fluency.

In these tests, they were asked to list as many words as possible that started with certain letters, or in a category such as animal names.

Dr. Yue Leng, who led the research at the University of California, San Francisco, said: 'Our findings suggest that it is the quality, not the quantity, of sleep that is particularly important for cognitive health in middle age.

'If someone is waking up at night due to the stress of work, or if they snore a lot and may have a condition called sleep apnea, which makes them restless, these are things they may want to address.

'They may be associated with poorer thinking skills and memory later in life.'

The study, published in the journal Neurology, also looked at how long people slept, but sleep duration was not found to be linked to thinking skills.

The people analyzed by researchers had taken part in a previous study, in which they wore a sleep tracker twice for three days in a row.

The two sleep measurements, conducted between 2003 and 2005, were taken about a year apart to determine people's average sleep quality, rather than a one-time snapshot.

Interrupted sleep was assessed based on the time people spent moving during the night, including periods when they remained still for no more than a minute at a time.

Researchers divided people into three groups and found a significant difference between the third with the worst sleep quality and the third with the best sleep.

The worst sleepers were almost three times more likely to do poorly on a thinking test that required them to remember which numbers belonged to a series of symbols.

The poorer performance in the tests was found after taking into account factors other than sleep that could play a role, including people's age and education, and conditions that could affect the brain, such as high blood pressure.

However, the study used wrist-worn trackers, rather than the gold standard sleep trackers that measure brain activity.