People who habitually rose before 5 a.m. had a 1.7 times greater risk of high blood pressure and were twice as likely to develop hardening of the arteries as those who got up two to three hours later, researchers in Kyoto found. The study, of 3,017 healthy adults aged 23 to 90, also found a possible link between vascular disease and early birds who began the day with vigorous exercise.

“The results are contrary to the commonly held belief that early birds are in better health,” said Mayuko Kadono, a physician at Kyoto Prefectural University of Medicine, who led the study. “We need to find what the causes of this are, and whether exercising after waking early is beneficial.”