Regularly getting less than six hours sleep a night raises the risk of stroke in middle age, research has shown.
Scientists in the US studied 5,666 people aged 45 and older who had no history of stroke and were of normal weight.
Over a three-year period they found that those who habitually slept for less than six hours were significantly more likely to suffer a stroke.
Having too little sleep had a greater effect than other stroke risk factors.
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The same pattern was not seen in overweight and obese individuals.
Lead researcher Dr Megan Ruiter, from the University of Alabama, said: "In employed middle-aged to older adults, relatively free of major risk factors for stroke such as obesity and sleep-disordered breathing, short sleep duration may exact its own negative influence on stroke development.
"We speculate that short sleep duration is a precursor to other traditional stroke risk factors, and once these traditional stroke risk factors are present, then perhaps they become stronger risk factors than sleep duration alone."
She presented the findings at the Sleep 2012 meeting currently taking place in Boston.
Further research supporting the results would suggest a need for more awareness of poor sleep as a stroke risk factor, said Dr Ruiter.
"Sleep and sleep-related behaviours are highly modifiable with cognitive behavioural therapy approaches and/or pharmaceutical interventions," she added. "These results may serve as a preliminary basis for using sleep treatments to prevent the development of stroke."
Another small study presented at the same meeting indicated that fear of the dark may contribute to insomnia.
Nearly half of a group of students who complained of lack of sleep also admitted to being afraid of the dark.
In tests, researchers found they produced jumpier responses to sudden noise bursts in dark surroundings.
"The poor sleepers were more easily startled in the dark compared with good sleepers," said study leader Taryn Moss, from Ryerson University in Toronto, Canada.
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