Sedentary lifestyle – not watching TV

"Experts claim being a couch potato can increase the risk of developing diabetes," the Daily Express reports.

A study of people at high risk of diabetes produced the sobering result that each hour of time spent watching TV increased the risk of type 2 diabetes by 2.1% (after being overweight was taken into account).

The study originally compared two interventions aimed at reducing the risk of developing diabetes compared to placebo. It involved 3,000 participants who were overweight, had high blood sugar levels and insulin resistance. These are early indications that they may be developing diabetes (often referred to as pre-diabetes). The interventions were either metformin (a drug used to treat diabetes) or a lifestyle intervention of diet and exercise.

This study used data collected from the original trial to see if there was a link between increased time spent watching the TV and risk of developing diabetes.

Across all of the groups they found a slightly increased risk, which was 3.4% per hour of TV watching when being overweight was not taken into account.

The findings may not be reliable, as researchers did not take other risk factors into account, such as family history of diabetes, use of other medication or smoking status. They also relied on self-reported TV watching times, which may not be very accurate.

That said, lack of exercise is a known risk factor for a range of chronic diseases – not just diabetes. Read more about why sitting too much is bad for your health.

Where did the story come from?

The study was carried out by researchers from the University of Pittsburgh, George Washington University, Pennington Biomedical Research Center and several other US universities. It was funded by many different US National Health Institutes and three private companies: Bristol-Myers Squibb, Parke-Davis and LifeScan Inc.

The main funding source was the National Institute of Diabetes and Digestive and Kidney Diseases of the US National Institutes of Health. One of the authors has a financial interest in a company called Omada, which develops online behaviour change programmes, with a focus on diabetes.

The study was published in the peer-reviewed medical journal Diabetologia.

The UK media has focused on the statistic that the risk of getting diabetes increases by 3.4% per hour of TV watched. However, this figure does not take into account the risk factor of being overweight. When this is accounted for, the increased risk is less, at 2.1%.

The Daily Express’s online headline "Watching too much TV can give you diabetes" would not be our preferred wording. Some readers may take it as a statement that their TV sends out dangerous rays that increase your blood sugar levels. A more accurate, if slightly less striking, headline would be "Sedentary behaviour increases your diabetes risk".

What kind of research was this?

This study looked at data from a randomised controlled trial that aimed to test whether lifestyle changes or the diabetes drug metformin reduced the risk of developing diabetes compared to placebo (dummy pill). It was conducted on over 3,000 people at high risk of diabetes. The trial found that metformin reduced the risk by 31% and that the lifestyle intervention reduced it by 58% compared to placebo.

This study aimed to see if the lifestyle intervention, which aimed to increase physical activity, had any effect in reducing the amount of self-reported time spent sitting. As a secondary outcome, the researchers looked at data from each group to see if there was an association between time spent sitting and the risk of diabetes. As this was not one of the aims of the study, the results of this type of secondary analysis are less reliable.

Critics of this approach argue that it is akin to "moving the goalposts"; researchers fail to get a striking result for their stated aim, so they then focus on a secondary aim that will get them the results.

What did the research involve?

Over 3,000 adults at high risk of diabetes were randomly allocated to take metformin, a placebo, or have a lifestyle intervention, from 1996 to 1999. They were followed up for an average of 3.2 years to see if any of the interventions reduced the risk of developing diabetes.

The lifestyle group had an "intensive" lifestyle intervention focusing on a healthy diet and exercise. The aim for this group was to achieve 7% weight loss and do at least 150 minutes of moderate intensity activity per week (the recommended minimal activity levels for adults). They were advised to limit inactive lifestyle choices, such as watching the TV. People given the metformin or placebo were also advised about a standard diet and had exercise recommendations. The study took place over 2.8 years.

A variety of measures were recorded, including weight and annual blood sugar tests. Each year, the participants were interviewed using a Modifiable Activity Questionnaire. This recorded self-reported estimates of leisure, TV watching and work-related activity.

In this analysis, the researchers compared the amount of time each person reported they spent watching the TV at the start and end of the study in each group.

What were the basic results?

Across all of the treatment groups, every hour per day of watching TV raised the risk of diabetes by 2.1%, after adjusting for age, sex, physical activity and weight. When the results did not take increased weight into account, the risk was higher, at 3.4% per hour.

By the end of the study, people in the lifestyle intervention group watched less TV. At the start of the study, each group reported watching a similar amount of TV – around 2 hours and 20 minutes per day. Three years later, people in the lifestyle group watched on average 22 minutes less per day. Those in the placebo group watched 8 minutes less, but those on metformin did not change their TV watching significantly.

How did the researchers interpret the results?

The researchers concluded that although it was not a primary goal of the study, "the lifestyle intervention was effective at reducing sedentary time". They report that "in all treatment arms, individuals with lower levels of sedentary time had a lower risk of developing diabetes". They advise that "future lifestyle intervention programmes should emphasise reducing television watching and other sedentary behaviours, in addition to increasing physical activity".

Conclusion

This study has found an association between TV watching and an increased risk of developing diabetes. However, there are many potential confounding factors that were not taken into account in the analysis. This includes other medical conditions, medication, family history of diabetes and smoking.

Additionally, all of the participants were at high risk of developing diabetes. They were overweight at the start of the study, had high blood sugar levels and insulin resistance – therefore, the study does not show whether this association would be found in people at low or moderate risk.

The original study did not set out to see if increased TV watching was associated with increased risk of developing diabetes; this was an afterthought, using the data that had been collected. This makes the results less reliable.

A further limitation is that the study is reliant on self-reporting the amount of time spent watching TV. This was estimated for the previous year, which is unlikely to be entirely accurate.

Watching TV is not "going to give you diabetes" as the Express had confusingly stated, but it is important to compensate for time spent being a couch potato by exercising regularly, eating a healthy diet and trying to achieve or maintain a healthy weight.

Read more about reducing your type 2 diabetes risk.