People who naturally stay up late put strain on their hearts as they age. A large study followed more than 300,000 adults and found that middle-aged and older night owls had poorer heart health and a higher risk of heart attack and stroke than morning types. This effect was more pronounced in women. Another study of 80,000 volunteers showed that people preferring the nocturnal style have a 25% higher probability of cardiovascular disease. Falling asleep late after midnight increases the risks, while the ideal time is between 10 and 11 p.m. Much of the increased risk comes from lifestyle factors for evening types, such as smoking and not getting enough sleep. Falling asleep early before 10:00 PM increases the risk by 12%.