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. The same pattern was not seen in overweight and obese individuals.
Lead researcher Dr Megan Ruiter, from the University of Alabama, said: "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."
Further research supporting the results would suggest a need for more awareness of poor sleep as a stroke risk factor, said Dr Ruiter.
Another small study presented at the Sleep 2012 meeting in Boston 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.