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Getting out on the proverbial "wrong side of the bed" has long been blamed for giving people a hostile demeanour; but now a study has shed light on what the real cause of grumpiness may be - and though it's related to your sleeping habits, it has nothing to do with how you get up.
Researchers at North Carolina's Duke University Medical Center have found that poor sleep may increase the likelihood of developing a raft of health problems, including type 2 diabetes, heart disease and depression.
Not getting enough kip can also contribute to feelings of hostility and anger, though the researchers found women were more likely to be made grumpy by a lack of sleep than men were.
"This is the first empirical evidence that supports what we have observed about the role of gender and its effects upon sleep and health," said Edward Suarez, an associate professor in the department of psychiatry and behavioral sciences at Duke and the lead author of the study.
"The study suggests that poor sleep - measured by the total amount of sleep, the degree of awakening during the night, and most importantly, how long it takes to get to sleep - may have more serious health consequences for women than for men."
Study participants were asked to complete a sleep quality questionnaire and to rate various aspects of their sleep over a period of one month.
Additional measures assessed the extent of any depression, anger, hostility and perceived social support from friends and family.
Both men and women participated in the test, although women on hormone therapy treatments - which have been shown to alter sleep patterns in some people - were excluded from the study.
All of the 210 participants were apparently healthy non-smokers.
Although none had a history of sleep disorders, the researchers found 40 per cent of participants took more than 30 minutes to fall asleep and woke frequently during the night - the mark of a "poor sleeper", according to the study.
And while their sleep quality ratings were similar, men and women were found to have dramatically different risk profiles.
"We found that for women, poor sleep is strongly associated with high levels of psychological distress, and greater feelings of hostility, depression and anger, said Suarez.
"In contrast, these feelings were not associated with the same degree of sleep disruption in men."
Blood samples taken from the participants were measured for levels of biomarkers associated with increased risk of heart disease and diabetes, including insulin and glucose levels, fibrinogen (a clotting factor) and two inflammatory proteins, interleukin-6 and C-reactive protein.
The study showed that women who reported they had trouble falling asleep also had higher insulin levels and higher levels of the inflammatory proteins associated with heart disease.
"Interestingly, it appears that it's not so much the overall poor sleep quality that was associated with greater risk, but rather the length of time it takes a person to fall asleep that takes the highest toll," said Suarez.
"Women who reported taking a half an hour or more to fall asleep showed the worst risk profile."
Suarez plans to conduct further studies into the relationship between health risk and poor sleep in men and women.
"Good sleep is related to good health. More research needs to be done to define gender-linked responses to poor sleep, including the role that sex hormones play over a lifetime and how sleep needs and responses change from childhood to maturity," he said.
* The Duke University Medical Center study was published in the journal Brain, Behavior and Immunity.
See video below for more on the study's findings
