People who sleep too much or too little may be more likely to have early signs of heart disease, according to a study of more than 47,000 apparently healthy young and middle-aged adults.

The study volunteers filled out sleep questionnaires and underwent tests to assess the arteries in their hearts and legs. Researchers found that people who slept for nine or more hours per night had more calcium buildup in their heart artery walls and stiffer leg arteries than those who slept seven hours per night.