People aged in their 30s and 40s who suffer from poor-quality sleep could experience memory and cognition problems much later, a study has shown.
Participants who had the most disrupted sleep were twice as likely to see a decline in their cognitive performance as those with the least interruption, the study, published in Neurology, said.
It was the quality of sleep that had the most impact, rather than the quantity, said author Dr Yue Leng of the University of California in San Francisco.
She said: "Given that signs of Alzheimer's disease start to accumulate in the brain several decades before symptoms begin, understanding the connection between sleep and cognition earlier in life is critical for understanding the role of sleep problems as a risk factor for the disease."
The study, published in the medical journal of the American Academy of Neurology, looked at 526 people, with an average age of 40, who have been studied for 11 years.
Participants recorded bedtimes and wake-up times in a sleep diary and wore a wrist activity monitor, similar to a Fitbit, for three consecutive days twice a year to calculate their averages.
They completed a sleep quality survey with scores ranging from zero to 21 – the higher scores indicated poorer quality - and some 239 people (46 per cent) had averages greater than five.
With the data taken into account, adjusted for age, gender, race and education, a total of 175 had the most disrupted sleep out of the whole group.
Of these, 44 had poor cognitive performance 10 years later.
Authors of the study stressed that the research does not necessarily prove that bad sleep quality causes cognitive decline, but that there is definitely an association.
Dr Leng said: "More research is needed to assess the link between sleep disturbances and cognition at different stages of life and to identify if critical life periods exist when sleep is more strongly associated with cognition."
The head of policy at Alzheimer's Research UK, Dr Susan Mitchell, told The Telegraph: "Without a detailed picture of what's going on in the brain, we don't know whether the disrupted sleep patterns are causing the decline in cognition, or if a decline in cognition is causing the disturbances.
"Many of us have experienced a bad night's sleep and know that it can have an impact on our memory and thinking in the short term. But there are still gaps in our knowledge around whether sleep disturbances in midlife can increase our risk of developing dementia in the future."
The research was funded by the US National Institute on Aging and the National Heart, Lung, and Blood Institute.
