Regularly sleeping too much or not enough may increase a persons chances of diabetes, heart attack, stroke and becoming obese, according to a new study.
Researchers examined the sleeping habits of more than 130,000 Korean men and women aged between 40-69 years and then conducted a range of medical tests to examine the impact of sleep on their health.
The study, published in BMC Public Health, found fewer than six hours sleep and more than ten hours of sleep per day was associated with metabolic syndrome (MetS) - a collection of conditions that often occur together and increase the risk of these diseases.
These include obesity, high blood pressure, high cholesterol and insulin resistance.
Less than six hours of sleep was associated with MetS and elevated waist circumference in men, and only a larger waist size among women.
Greater than 10 hours of sleep was associated with MetS and elevated triglycerides (fats in blood) among both men and women and with elevated waist circumference.
Reduced HDL cholesterol, the 'good' cholesterol, and elevated fasting glucose was associated among women only.
"We observed a potential gender difference between sleep duration and metabolic syndrome, with an association between metabolic syndrome and long sleep in women and metabolic syndrome and short sleep in men," said lead author Claire Kim.
The biological reasons that underlie the associations remained unclear, however the authors suggested hormones could play a factor.
Elevated levels of hormones leptin and ghrelin can increase appetite and caloric intake or reduce energy expenditure in people who sleep less than seven hours per day, which may lead to increased waist circumference and development of obesity, they say.
"It may also cause impaired glycemic control (lowering glucose tolerance and thyrotropin concentration levels) increasing risk for hypertension and diabetes," they wrote.
The authors caution that this was only an observational study and does not draw conclusions about cause and effect.