High television viewing and low physical activity in early and mid-adulthood may raise the risk of poorer cognitive function later in life, according to new research.

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Watching too much TV – defined in the study as at least 4 hours daily – between the ages of 18 and 30 may lead to poorer cognitive function in mid-life.

Study co-author Tina Hoang, of the Northern California Institute of Research and Education (NCIRE) in San Francisco, and colleagues recently presented their findings at the 2015 Alzheimer’s Association International Conference (AAIC) in Washington, DC.

The 2008 Physical Activity Guidelines for Americans state that adults aged 18-64 should engage in at least 150 minutes of moderate-intensity aerobic activity or 75 minutes of vigorous-intensity aerobic activity each week. According to the Centers for Disease Control and Prevention (CDC), however, only around 1 in 5 adults meet these recommendations.

It is well established that lack of physical activity and sedentary behavior can have negative implications for health, such as overweight and obesity, greater risk of type 2 diabetes and increased risk of cardiovascular disease. Increasingly, research has suggested such behavior may also adversely affect brain function.

Previous studies have shown physical activity in later life may protect against cognitive decline and dementia. However, Hoang and colleagues note that little is known about the role physical activity in early adulthood plays in later-life brain function.

“Understanding this relationship in early adulthood may be particularly important because global data suggests that levels of physical inactivity and sedentary behavior are increasing,” says Hoang.

The team’s study included more than 3,200 adults aged 18-30 who were part of the Coronary Artery Risk Development in Young Adults (CARDIA) Study.

Over 25 years, the researchers recorded participants’ television viewing time and physical activity levels via a minimum of three assessments.

In the study, high television viewing was defined as more than 4 hours daily, while low physical activity was defined as activity below 300 Kcal per 50-minute session, three times weekly. If participants met these definitions in more than two thirds of assessments, they were deemed as having a long-term pattern of high television viewing and low physical activity.

At the end of the 25-year study period, participants took part in tests that assessed their cognitive function, including memory, executive function and processing speed.

Seventeen percent of participants had a long-term pattern of low physical activity over the 25 years, 11% had a long-term pattern of high television viewing and 3% had a long-term pattern of both.

The researchers found that high television viewing and low physical activity among participants were independently associated with significantly poorer cognitive function in mid-life, while subjects with both factors were nearly two times more likely to have worse cognitive function in mid-life.

Commenting on their results, Hoang says:

Our findings demonstrate that even early and mid-adulthood may be critical periods for promotion of physical activity for healthy cognitive aging.

Sedentary behaviors, like TV viewing, could be especially relevant for future generations of adults due to the growing use of screen-based technologies. Because research indicates that Alzheimer’s and other dementias develop over several decades, increasing physical activity and reducing sedentary behavior beginning in early adulthood may have a significant public health impact.”

Yesterday, Medical News Today reported on another study presented at the AAIC, in which researchers revealed how a simple saliva test could predict a person’s risk of Alzheimer’s.