Back in 1951, Motorola still had to explain what a TV could mean for a family, as this Saturday Evening Post ad exclaims. Entertainment all day long for mom! Relaxation after work for dad! Education for the kids! And for the older folks, hours of happiness without leaving home!

It got me wondering again about the effect of all that television on older folks. They watch more TV than any other group. Qccording to the American Time Use Survey, the average American over 65 watches about four and a half hours of TV every day, 30 minutes more than they did 15 years ago, as shown in this graphic from Quartz.

And all those hours of happiness without leaving home are having an effect. One study found that too much television "is associated with negative changes in many aspects of health including cardiovascular, bone health and cellular function. Television use in particular has been linked with greater risk for obesity and Type2 diabetes, lower life satisfaction, less frequent engagement in social and physical interaction, and increased risk for dementia."

More recently, an English study determined that television viewing for more than 3.5 hours per day could contribute to cognitive decline. It was associated with poorer verbal memory six years later with evidence of a dose-response relationship: greater hours of television per day were associated with poorer verbal memory at follow up.

The study notes that watching television is "as a proxy for sedentary behaviour," which has been linked to cognitive decline, and is different from using a computer.

However, other sedentary activities such as using the internet are not associated with cognitive decline and might even contribute to cognitive preservation and reduced dementia risk, which suggests that the sedentary nature of television watching does not solely explain its longitudinal associations with cognition.

So television is different; it does something to your brain. Bill Andrews at Discover Magazine thinks this makes sense:

Think about it: TV combines intense and fast-changing multi-sensory stimuli with almost total passivity. Your brain gets a workout, but your body sits still. This "alert-passive interaction" could fuel a kind of cognitive stress that ends up taxing our verbal memory skills.

It's not just in your mind.

man and cat look at TV turned into fish tank Maybe we'd be better off we followed his lead and turned our television sets into fish tanks. (Photo: Hulton Archive/Getty Images)

An American study sponsored by the National Institutes of Health and AARP followed 134,000 participants over 10 years and found that the more time you spend sitting around and watching television, the greater chance you will develop disabilities, and that you have turn the TV off and get some exercise. "More than three hours of TV a day coupled with less than three hours a week of physical activity was the worst combination, and raised people's risk of disability more than three-fold compared to those who watched the least TV and got the most exercise."

In sum, our findings and those of others indicate that reductions in sedentary time, as well as increases in physical activity, are necessary to maintain health and function in older age — particularly among those who are the least active. Current U.S. public health recommendations for physical activity have not addressed sedentary time, but our results suggest doing so may be useful for reducing mobility disability. Given aging demographics and the global economic burden associated with aging- and disuse-related disability, there is a tremendous public health benefit to understanding the extent to which those determinants of mobility disability can be modified in older age.

The lead study author, Loretta DiPietro, said in a statement: "Sitting and watching TV for long periods (especially in the evening) has got to be one of the most dangerous things that older people can do because they are much more susceptible to the damages of physical inactivity."

DiPietro concludes: "Our findings suggest that older people who want to remain fit must ramp up their daily physical activity and reduce the amount of time they spend sitting."

I wonder how the smartphone or tablet changes things? The American Time Use study included streaming on phones and tablets as watching TV; the British study on cognitive decline found that TV had a different effect on the brain than using a computer. Yet really, our computers and our TVs and our smartphones are all merging into one entertainment device with the difference being the size of the screen.

Probably the most straightforward answer is that sitting on the sofa staring at anything is bad for your body, and a diet of passively watching "Friends" and "Gilligan's Island" reruns is bad for your mind. And Motorola got it wrong in that ad; getting up and leaving home for a little exercise is a very good idea at any age.

Lloyd Alter ( @lloydalter ) writes about smart (and dumb) tech with a side of design and a dash of boomer angst.

Too much TV is bad for your health, and older people are watching it more than ever
Older people are watching more television than ever — about 4.5 hours a day — and more than any other group.