Those who choose to spend their evenings sat in front of the TV could be inadvertently increasing their risk of diabetes, research suggests.
Scientists have warned that every hour spent watching television increases the chance of developing the condition by 3.4% in high-risk individuals.
An American study looked at data from more than 3,000 overweight adults participating in a Diabetes Prevention Programme (DPP) who were given either a placebo, metformin drug (used for diabetes) or took part in a lifestyle intervention scheme.
Researchers looked at whether, as well as increasing activity levels, the lifestyle intervention also made those taking part spend less time sitting.
Prior to the trial all three groups had reported spending an average of around two hours and 20 minutes a day watching TV.
But the team found that while the placebo and metformin groups spent an average of just nine and six minutes less in front of the TV respectively, those taking part in the lifestyle scheme sat and watched it for 37 minutes less per day on average.
The authors then investigated the impact of sedentary behaviour over time on diabetes incidence and found for all participants, the risk of developing diabetes increased approximately 3.4% for each hour spent watching TV after adjustment for age, sex, intervention and time-dependent leisure physical activity.
"Future lifestyle intervention programmes should emphasise reducing television watching and other sedentary behaviours in addition to increasing physical activity," the study said.
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Researchers also found that subsequent changes in body weight may account for some of the relationship between sitting behaviour changes and diabetes development.
Senior author Dr Andrea Kriska, of the University of Pittsburgh, Pennsylvania, said: "These findings are particularly noteworthy because a decrease in sitting occurred, despite the absence of programme goals aimed at reducing sitting.
"It is likely that a lifestyle intervention programme that incorporates a specific goal of decreasing sitting time would result in greater changes in sitting and likely more health improvements than are demonstrated here.
"Finally, these results should inform future intervention efforts that already focus on goals of increasing activity and reducing weight to also consider emphasising sitting less."
The study is published in Diabetologia (the journal of the European Association for the Study of Diabetes).