Let it never be said that the life of a couch potato is an easy one in spite of all appearances to the contrary. Habitual sofa squatters put their lives on the line for the sake of a few extra hours of R&R;, a double feature or two, or a simple season-long marathon of their favorite TV shows.

The cost of all that sitting over the years can spell not only a greater risk of heart disease, diabetes and certain kinds of cancer. Couch potatoes may also have smaller brains.

Failing to maintain adequate levels of physical fitness in middle age can not only shrink your muscles but also potentially reduce brain volume decades later, according to a study released in the journal Neurology.

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For their study, researchers enlisted more than 1,583 middle-aged participants who did not have dementia or heart disease. Those individuals took a simple physical fitness test using a treadmill, while researchers monitored heart rate and blood pressure. The participants also underwent an MRI scan.

Two decades later, the same group repeated the treadmill test and received another MRI scan. The researchers analyzed the results with and without the inclusion of those who had developed heart disease or were taking medication to control blood pressure.

Those who performed worse on the fitness tests were more likely to show smaller brain volume two decades later. Those who fared especially poorly on the physical fitness tests exhibited brain volume reduction equivalent to years of accelerated aging, the researchers found.

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Because the study is observational, the researchers cannot prove causation, but they have demonstrated a direct correlation between poor physical fitness and decreased brain volume.

The Neurology study is hardly the first to show a potential link between exercise and a healthier brain. Earlier this week, researchers in Suomen Akatemia in Finland, who published their findings in the Journal of Physiology, found that aerobic exercise had beneficial effects on brain structure and function.

The hippocampus is a part of the brain important in learning. What the Finnish researchers learned was that running and other forms of sustained aerobic exercise can promote neurogenesis, or neuron growth.

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The benefits to the brain were most pronounced as a result of sustained long-distance. High-intensity interval training (HIIT) were minor, and resistance training appeared to offer no brain gains at all.

No one has ever gone to the gym intending to boost the health and size of their brains. But the next time you’re on the couch looking for a reason to get up and go, consider that continuing to slack off on the workouts will not only increase your waistline, it might also shrink your brain.