The study's sample included 63,048 males ages 45-65 from the Australian state of New South Wales. Study participants reported the presence or absence of various chronic diseases, along with their daily sitting time: categorized as less than four hours, four to six hours, six to eight hours, or more than eight hours.
Compared with those who reported sitting four hours or less per day, those who sat for more than four hours per day were significantly more likely to report having a chronic disease such as cancer, diabetes, heart disease and high blood pressure. The reporting of chronic diseases rose as participants indicated they sat more. Those sitting for at least six hours were significantly more likely to report having diabetes.
"We saw a steady stair-step increase in risk of chronic diseases the more participants sat," Rosenkranz said. "The group sitting more than eight hours clearly had the highest risk."
The study is relevant to office workers sitting at desks and those sitting for long periods of time such as truck drivers, he said.
"We know that with very high confidence that more physically active people do better with regard to chronic disease compared with less physically active people, but we should also be looking at reducing sitting," Rosenkranz said. "A lot of office jobs that require long periods of sitting may be hazardous to your health because of inactivity and the low levels of energy expenditure."
Researchers said that although most of the current evidence is suggestive of a causal connection, they cannot be certain in this study whether volumes of sitting time led to the development of chronic diseases or whether the chronic diseases influenced sitting time.
"It's a classic case of, 'Which came first: the chicken or the egg?'" Rosenkranz said.
The study has been published in the International Journal of Behavioral Nutrition and Physical Activity.