March 30, 2009 (Orlando) -- Burning the midnight oil may be hazardous to your health.
Several large studies have linked chronic sleep loss to heart disease, diabetes, obesity, and other health problems, says Yu Misao, MD, of the Misao Health Clinic in Gifu, Japan.
But whether bedtimes also have an influence on heart health has not been explored, he tells WebMD.
Too Little Sleep Affects Heart Health
So Misao and colleagues put that question to the test in a study of 251 healthy men 60 and younger. They had an annual checkup, during which their blood pressure, body weight, body mass index (BMI), waist circumference, and lipid levels were measured.
Brachial-ankle pulse wave velocity was used to examine the men for evidence of arterial stiffening. This measures how fast blood is rushing between the brachial artery in the arm and the tibial artery in the ankle. When blood pressure is high, blood flow accelerates, and the arterial walls stiffen.
All the participants filled out questionnaires that asked how many hours of sleep they got each night (six hours and 20 minutes, on average) and what time they went to bed (11:30 p.m. on average).
The fewer hours a man slept each night, the higher his BMI, blood pressure, and triglyceride levels, the study showed.
“This is consistent with previous reports showing that short sleep duration may negatively affect cardiovascular risk factors, Misao says.
There was no significant relationship between how many hours a man slept and arterial stiffness.
Late Bedtimes Linked to Arterial Stiffness
The men were then divided put into three groups according to the number of hours they reported sleeping at night: less than six hours, six to seven hours, and seven hours or more.
In each of these groups, the men who reported going to bed before midnight had more relaxed arteries, as shown by significantly lower brachial-ankle pulse wave velocity levels, than the men who went to bed after midnight.
The findings were presented at the American College of Cardiology’s 58th Annual Scientific Sessions.
“While the study doesn’t tells us why, a previous study suggested that people who go to bed late might eat more at night,” Misao says. Evening snacking may raise the risk of obesity, a risk factor for heart disease, he says.
Other research suggests that turning in after midnight might activate the sympathetic nervous system, which accelerates body functions, including heart rate, and helps control how the body responds to stress, Misao says.
Daniel Jones, MD, past president of the American Heart Association and dean of the University of Mississippi School of Medicine, says it’s possible that “there’s some physiological [explanation] for the finding.”
For example, turning in after midnight might throw your internal biological clock out of synch, he says.
“But people who go to bed late are different from people who go to bed early. They may be more likely to smoke. They may be more likely to drink, They may be more likely to overeat. These are all heart disease risk factors that [weren’t taken into account in the analysis],” Jones tells WebMD.
At this point, “I wouldn’t recommend changes in my sleep behavior based on this study,” he says.
Misao agrees that further research is needed.
“From the point of view of preventing cardiovascular disease, we have to focus not only on diet and exercise, but also on how we sleep, including when we go to bed,” he says.