This Is How Much Sleep You Need to Avoid Diabetes, Heart Disease and Stroke Risk

Sleeping too much or too little has been linked to a cluster of conditions which raise the risk of heart disease, stroke and diabetes.

A team of scientists in South Korea investigated the association between sleep and a condition known as metabolic syndrome, characterized by excess fat around the waist, increased blood pressure, high blood sugar levels, and out of kilter cholesterol or triglyceride levels.

In what is believed to be the largest study to look into how long a person sleeps and the risks of metabolic syndrome separately for men and women, the researchers at the Seoul National University College of Medicine analyzed data from HEXA.

The study was carried out in Korea between 2004 to 2013, and includes information on demographics, medical history, medication use, diet, and exercise levels. Samples of bodily fluids including urine and plasma were also collected from the participants.

Overall, 29 percent of men and 24 percent of women studied had metabolic syndrome.

The paper published in the journal BMC Public Health investigated data on over 133,000 Korean men and women aged between 40 to 69 years of age. They were asked: "In the past year, on average, how many hours/minutes of sleep (including daytime naps) did you take per day?" The study didn't differentiate between nighttime sleep and naps during the day.

Their responses revealed that, on average, those who slept fewer than six and more than ten hours were at higher risk of metabolic syndrome than those who slept between six to seven hours a day.

Men who slept fewer than six hours (11 percent of the sample) were more likely to have metabolic syndrome and a larger waist. Women who slept fewer than six hours (13 percent of the sample) were more likely to have a larger waist.

Men who slept more than ten hours per day (1.5 percent of sample) were linked to metabolic syndrome and higher than normal levels of triglycerides. Women who slept too much (1.7 percent of sample) carried a risk of higher triglycerides, metabolic syndrome, higher waist circumference, and blood sugar as well as low levels of "good" cholesterol HDL-C.

Claire E. Kim, lead author of the study at the Department of Preventive Medicine at Seoul National University College of Medicine, said in a statement: "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."

But the study stopped short of finding a cause and effect tie between sleep and metabolic syndrome. Now, more research is needed to identify the biological mechanisms behind this association. Scientists believe it could be due to a shift in hormones that boost the appetite or those who get fewer hours of sleep being less active.

The new findings follow a separate study which linked too much or too little sleep with developing dementia. A team of researchers at Kyushu University in Japan found the risk of dementia and early mortality was "significantly greater" in those who slept fewer than five hours or more than 10 hours, compared to those who sleep between five to 6.9 hours.