Late nights linked to stiffer arteries3rd April 2009
Researchers in Japan have come to the conclusion that staying up late has negative long-term consequences.
Studying men who slept after midnight, researchers found that they tend to have more stiffening of the arteries.
This stiffness could indicate the beginning stages of atherosclerosis, a chronic inflammatory response in the walls of arteries due to the accumulation of white blood cells.
Yu Misao of the Misao Health Clinic, who conducted the study, said that chronic sleep loss had already been linked to diabetes, obesity, heart disease, and other health problems.
Researchers focused their efforts on 251 otherwise healthy men, none of them older than age 60.
After an annual checkup, the men's blood pressure, body weight and mass according to the body mass index (BMI), waist circumference, and lipids were measured.
Then they were examined for arterial stiffening using a method which measures the speed of blood through the heart.
Faster blood means higher blood pressure, which in turn signifies stiffness of arterial walls.
Participants also filled out questionnaires about the number of hours of sleep they got each night.
They averaged just over six hours of sleep, with a bedtime of 11:30 pm.
The study showed that triglyceride levels went up as the number of hours a man slept went down.
BMI and blood pressure also went up as a result.
Misao said the results were consistent with previous reports showing that short sleep duration may negatively affect cardiovascular risk factors.
After the initial phase of the study, the men were divided into three groups.
Men who slept less than six hours a night formed one group, men who slept anywhere from six to seven hours a second group, and men who slept more than seven hours a third group.
In each group, men who slept before midnight had less artery stiffening, showing that the amount of artery stiffness and the amount of sleep each man had were unrelated.
Misao said that, while the study doesn't explain why, a previous study suggested that people who go to bed late might eat more at night.
Daniel Jones, past president of the American Heart Association said it was possible there was a physiological explanation for the finding.
He also said that people who go to bed late are different from people who go to bed early, and that they may be more likely to smoke, drink, or overeat.
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