Millions of Americans will do something today that researchers believe could be incredibly unhealthy for them.

The problem though is this daily activity has become so common, so frequent people think little of it.

It’s binge watching TV.

While there isn’t necessarily a formal definition for “binge watching” there is an agreement among researchers that watching over three hours of TV and failing to exercise are a perfect storm of factors contributing to poor health.

A recent study by the Northern California Institute for Research and Education at the Veterans Affairs Medical Center in San Francisco has found a stunning association between binge watching and what happens to you later in life.

After surveying 3,200 participants over 25 years the study’s authors found that when people watched more than three hours of TV a day and didn’t exercise it made them less intelligent.

According to the researcher’s definitions anyone who was a classic “binge watcher” (that’s a modern term) was someone who watched in excess of 3 hours of TV per day, every day (21 hours a week or 1092 hours a year).

The researchers calculated physical activity by exercise units. These units were measured using a combination of duration of exercise with intensity of exercise. Those who scored low on physical activity were below the baseline number of exercise units for their sex, the study said.

Mental capacity was assessed by testing that looked at verbal memory skills, and the ability and speed with which participants were able to plan, organize and perform mental tasks.

In the end, the investigators found that 11 percent of the study volunteers were high TV-watchers. At middle-age, high TV-watchers were more likely to fare poorly on most mental function testing compared with low TV-watchers, the study found. The one exception the researchers discovered was that high TV-watchers did not fare worse in terms of verbal memory.

Those whose physical activity levels were ranked as low (about 16 percent of participants) were significantly more likely than those ranked high to fare poorly in terms of the ability to think quickly and perform mental tasks, the study found.

And participants who were both high TV-viewers and low exercisers had up to double the risk for poor mental performance by middle-age, compared with those who had been both low TV consumers and more physically active during young adulthood, the findings showed.

The researchers tried to make this study as fair as possible and took factors like substance abuse problems, obesity, poor nutrition, etc. among others into consideration when they were researching.

They also noted the research wasn’t conclusive.

One psychologist said , “there are too many variables and confounding factors to say that the behaviors of TV watching and a sedentary lifestyle is a direct ticket to cognitive deficits.”

All this being said the recommendation of keeping your TV watching habits well below what this survey determined was unsafe is advisable.

That way you’ll be healthier (and you’ll be more interesting).