Researchers in Australia found that prolonged television viewing was linked to an increased risk of death, even in people who exercised regularly,
recommended more be done to encourage people to spend fewer hours sitting still in front of the TV.
The study, which appeared online on 11 January in the journal Circulation, is the work of lead author Dr David Dunstan, a researcher at the Baker IDI Heart and Diabetes Institute in Melbourne, and colleagues.
The researchers wrote that studies have been done on television viewing time and health, but these have focused on links with cardiovascular risk, and not risk of death. So for this study they investigated the link between prolonged television viewing time and all-cause, cardiovascular, cancer and non- cardiovascular/non-cancer mortality in Australian adults.
One of the surprising things they found was that even for people who exercised regularly, the risk of death went up the longer they spent in front of the TV: they suggest the problem was the prolonged periods of sitting still.
For six years, Dunstan and colleagues followed 8,800 people aged 25 and over who were taking part in the Australian Diabetes, Obesity and Lifestyle Study (AusDiab) and found that those who said they watched four or more of TV a day were 46 per cent more likely to die of any cause and 80 per cent more likely to die of cardiovascular disease compared to people who said they spent less than two hours a day in front of their TVs.
The study revealed the following results:
- The average age of the participants at enrollment in 1999-2000 was 50 years.
- 284 deaths occurred over 58,087 person-years of follow up: 87 due to cardiovascular disease and 125 due to cancer.
- After adjusting for age, sex, waist size, and exercise, the risk of dying from all causes, cardiovascular disease and cancer went up for each extra hour spent sitting still in front of the TV every day.
- Risk of dying from any cause went up by 11 per cent for each extra TV viewing hour (hazard ratio [HR] for each one-hour increment was 1.11, with 95 per cent confidence interval [CI] ranging from 1.03 to 1.20).
- Risk of dying from cardiovascular disease went up 18 per cent for each extra hour (HR 1.18, 95%CI 1.03-1.35).
- Risk of dying from cancer went up 9 per cent for each extra hour (HR 1.09, 95%CI 0.96-1.23).
- Watching TV for 2 to 4 hours a day increased the risk of dying from any cause by 13 per cent (adjusted HR 1.13 95%CI 0.87-1.36), and from cardiovascular disease by 19 per cent (adj HR 1.19, 95% CI, 0.72 to 1.99) compared to watching it for less than 2 hours.
- Watching TV for 4 hours or more increased the risk of dying from any cause by 46 per cent (adj HR1.46, 95%CI 1.04-2.05), and from cardiovascular disease by 80 per cent (adj HR 1.80, 95%CI, 1.00 to 3.25) compared to daily TV viewing of under 2 hours.
- The links with cancer mortality and non-cardiovascular/non-cancer mortality were not significant.
"Television viewing time was associated with increased risk of all-cause and CVD mortality."
They recommended that as well as promoting exercise, reducing prolonged periods of sitting in front of the TV would help prevent chronic diseases.
This study points to a possible gap in public health messages.
While it is widely acknowledged that sitting for hours on end in front TVs, computer and video game screens has contributed to the obesity epidemic in the US and many other nations around the world, the resulting public health message has tended to encourage people to stop doing these sedentary activities and take up physical exercise like play football, swim, or use a treadmill.
But as Dunstan explained to the press, this study highlights a different view of the problem:
"It's not the sweaty type of exercise we're losing," said Dunstan.
"It's the incidental moving around, walking around, standing up and utilizing muscles that [doesn't happen] when we're plunked on a couch in front of a television."
In fact the participants in this study reported exercising on average between 30 and 45 minutes a day.
There is emerging evidence that prolonged periods of inactivity affects how our bodies process fats and other substances in a way that contributes to heart risk, and that avoiding sitting for long periods can reduce that effect.
Dr Marc Hamilton, a scientist at Pennnington Biomedical Research Center, Baton Rouge in Louisiana, USA, studies the biology of inactivity. He wasn't involved in this study, but said in a press statement issued by Baker IDI that:
"If you're not up on your feet moving around, you're sedentary."
A study by Nielsen Co, a ratings company, found that Americans spent an average of 151 hours a month viewing the TV during the fourth quarter of 2008, which is more than five hours a day.
Dunstan said their study findings are probably also valid for other sedentary activities such as sitting in front of a computer, reading a book, driving, or sitting on a bus or train. He said a recent study in Canada showed that the more time spent sitting for any reason was linked to a higher risk of death from heart-related and also from any cause.
He was also keen to point out that none of these findings detract from the importance of also doing exercise that makes you sweat and increases your heart rate.
However, consider this, when you have had your 8 hours sleep, and you have done your 30 to 60 minutes exercise every day, what are you doing for the other 15 hours?
"The implication of these findings is that the extraordinary amount of sitting can undo the good effects that we know are a benefit when we get regular exercise," said Dunstan, explaining that research has revealed muscle movement helps the body process blood sugar and blood fats:
"The absence of movement can slow down our metabolic processes," he explained, adding that:
"When we're sitting down or even lying on the couch, we're burning the equivalent of the energy we burn when we're sleeping."
The authors said one limitation of the study was that the data on TV viewing time and exercise was taken at enrollment and not verified after that; however they insist the findings are consistent with other research.
Hamilton cautioned that while population-based studies such as this one can only show links and not causes, he said that his own research into what happens when people and animals become inactive support these findings.
For example, after a few hours of being inactive, our bodies switch off an enzyme called lipoprotein lipase that pulls fat from the bloodstream. This results in less fat being transported to muscle tissue in readiness for burning as fuel, and more of it circulating in the blood, increasing the risk of arterial damage and subsequent cardiovascular diseases.
Hamilton said that one day of inactivity leads to a 20 per cent fall in our levels of good cholesterol or HDL, the one that helps move the bad cholesterol or LDL out of the bloodstream.
Other experts also suggest it's not just about making sure get intense exercise, while that is also important, we need to add more routine movement to our daily lives.
In fact, some say even standing still is better than sitting still.
Dr Gerard Fletcher, a cardiologist at Mayo Clinic, Jacksonville, in Florida, USA, works at his computer standing up:
"When you stand up, you shuffle around a little bit" said Fletcher: you use muscles not required when you're sitting or lying down.
"Television Viewing Time and Mortality. The Australian Diabetes, Obesity and Lifestyle Study (AusDiab)."
D. W. Dunstan, E. L.M. Barr, G. N. Healy, J. Salmon, J. E. Shaw, B. Balkau, D. J. Magliano, A. J. Cameron, P. Z. Zimmet, and N. Owen.
Circulation, Published Online on January 11, 2010.
Source: Baker IDI.
Written by: Catharine Paddock, PhD