Women who don’t get enough sleep and those who sleep too much may both run a greater risk of getting heart disease than those who log eight hours a day, according to a report published on Monday.

Why too much sleep would lead to coronary heart disease is unclear, the report said. In terms of sleep deprivation, previous studies have indicated high blood pressure can result.

The findings are the latest to emerge from a study of 121,700 U.S. female nurses that began in 1976.

More than 71,000 women in the study were asked in 1986 about their sleep habits. At the time they did not have heart disease. Ten years later researchers found there had been 934 heart attacks among them, 271 of them fatal.

After taking into account such things as snoring, smoking and body mass index, the researchers concluded that the relative risk of coronary heart disease among those who said they got five hours of sleep or less per day was 45 percent higher.