Sleeping more than nine hours a night, and sitting too much during the day could be a hazardous combination, particularly when added to a lack of exercise, according to the findings by the Sax Institute's '45 and Up Study'.
Too much sitting equates to more than 7 hours a day and too little exercise is defined as less than 150 minutes a week.
"When you add a lack of exercise into the mix, you get a type of 'triple whammy' effect," said Melody Ding from the University of Sydney, who led the study.
The researchers looked at lifestyle behaviours that are already known to increase the risk of death and disease - smoking, high alcohol intake, poor diet and being physically inactive - and added excess sitting time and too little/too much sleep into the equation.
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They then looked at different combinations of all of these risk factors to see which groupings had the most impact on a person's risk of dying prematurely from any cause.
"These non-communicable diseases (such as heart disease, diabetes and cancer) now kill more than 38 million people around the world - and cause more deaths than infectious disease," said Adrian Bauman, a professor at the University of Sydney.
The findings were published in the journal PLOS Medicine.