Young adults who shun exercise and spend large amounts of time in front of screens are twice as likely to have poor cognitive function in mid-life, according to a study.

The risk of cognitive decline by middle age, leading to Alzheimer’s and other forms of dementia, is greatly increased if adults fail to embrace a healthy lifestyle from the ages of 18 to 30, found researchers who presented their work at the Alzheimer’s Association International Conference 2015 in Washington, D.C.

Although physical activity is known to help guard against dementia in later life, little is known about the role it plays in early adulthood.

“Understanding this relationship in early adulthood may be particularly important because global data suggests levels of physical inactivity and sedentary behaviour are increasing,” said Tina Hoang of the Northern California Institute of Research and Education (NCIRE).

Hoang worked with her mentor – Kristine Yaffe, MD, of the University of California – and colleagues to investigate the association of long-term patterns of low physical activity and high television viewing time over 25 years with cognitive function at mid-life.

The researchers reported that study participants with low levels of physical activity over 25 years had significantly worse cognition in mid-life, adjusting for age, race, sex, education, smoking, alcohol, BMI, and hypertension. Similarly, participants with high levels of TV watching over 25 years also had significantly worse mid-life cognitive function. Study participants with both long-term low physical activity and high television viewing were almost two times more likely to have poor cognitive function in mid-life.

“Our findings demonstrate that even early- and mid-adulthood may be critical periods for promotion of physical activity for healthy cognitive ageing,” Hoang said.

“Sedentary behaviours, 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 behaviour beginning in early adulthood may have a significant public health impact.”